Monday, March 12, 2012

Unit 2



Table of Contents
Biology in the News
How the Body Senses a Range of Hot Temperatures
Chapter 17
The Cell Cycle Creates New Cells
Replication, Transcription, and Translation: An Overview
Cell Reproduction: One Cell Becomes Two
How Cell Reproduction is regulated
Environmental Factors Influence Cell Differentiation
Cloning an Organism Requires an Undifferentiated Cell
Therapeutic Cloning: Tissues and Organs
Triplet Code
Chapter 18
Tumors can be Benign or Cancerous
Cancerous Cells Lose Control of their Functions and Structures
How Cancer Develops
Advances in Diagnosis Enable Early Detection
Cancer Treatments
The 10 Most Common Cancers
Most Cancers can be prevented
Chapter 19
Your Genotype is the Genetic Basis of your Phenotype
Genetic Inheritance Follows Certain Patterns
Other Dominance Patterns
Other Factors Influence Inheritance Patterns and Phenotype
Sex-linked Inheritance: X and Y Chromosomes Carry Different Genes
Chromosomes May be Altered in Number or Structure
Many Inherited Genetic Disorders Involve Recessive Alleles
Chapter 20
DNA Sequencing Reveals Structure of DNA
DNA can be cloned in the Laboratory
Genetic Engineering Creates Transgenic Organisms
Gene Therapy: The Hope of the Future?

Biology in the News
In Science Daily, I read an article titled How the Body Senses a Range of Hot Temperatures.  Over the past two decades researchers have been studying how the human body senses many different temperatures.  Until recently the research has shown that proteins on the surface of nerve cells let the body feel a range of temperatures from extremely hot to warm.  Now research is showing that there are only a few proteins, called ion channels that distinguish many different temperatures.  All the research was recently published in the Journal of Biological Chemistry.  
                Research shows that ion channels are located in pores in the cell membrane.  The ion channels can turn sensors on or off by choosing if charged ions can go through the channels.  New information shows when the temperature sensors combine they create heteromeric channels that can sense temperature between what the original channels can detect.  One heteromeric channel I thought was very interesting was the TRPV3.  This channel responds to temperatures of approximately 85 degrees (Fahrenheit) and can sense flavors such as cinnamon, vanilla, oregano, and rosemary.  When the TRPV3 combines with another channel called TRPV1 the result is temperature response is at 92 degrees.  The study also showed that heteromeric channels had a higher sensitivity than the original channels that created it.  It is interesting that the sensors that sense heat also sense flavors too.  Researchers hope that in the future this information can possibly treat temperature sensitivity disorders.
Chapter 17
The Cell Cycle Creates New Cells

Replication, Transcription, and Translation: An Overview
Human DNA is made up of 46 chromosomes (23 exact pairs).  DNA replication is the process of coping DNA before cell division.  A gene is segment of DNA that contains a code or recipe.  

(http://en.wikipedia.org/wiki/Gene, accessed 20 Feb 2012)
A gene is the smallest functional unit of DNA and every unit produces a specific outcome.  One arm and leg of a chromosome is called a chromatid and the other arm and leg of the chromosome is called a sister chromatid. 
The process of replication is unzipping and uncoiling DNA strands.  Each strand serves as a template for the creation of a new DNA strand.  DNA nucleotides are linked and positioned by DNA polymerase moving nucleotides into their place.   Nothing is left to chance, precise base pairing guarantees an exact copy is made.  A centromere holds duplicate daughter (sister chromatids) chromosomes together.  Some mistakes are made in the DNA code occurring most often during DNA replication.  Some mistakes happen due to drugs, in vitro toxins, or viruses.  Sometimes there is no effect to cell mutations and other times cell mutations can result in cell death or cancer.  Repair enzymes try to repair mutations and some are fixed. 
Transcription is the process of copying DNA of a gene and turning it into mRNA (messenger ribonucleic acid).  It is the process of converting a gene code to RNA form.   DNA within the region of a gene starts to unwind.  RNA polymerase assists in copying the base sequence in the RNA nucleotides.  The primary transcript is made including introns and exons.  Introns are edited by enzymes to get rid of any sections that don’t carry genetic information.  The parts of the introns that don’t serve a purpose dissolve back into raw cell material.  Exons carry sequences of genetic information that is linked correctly and end up with messenger RNA strand.  It is a message that is in template form that is translated into a specific sequence of amino acids.  This message is in an encrypted code know as a triple code.  It is called triple code because it has three bases of mRNA called codons.   In a DNA molecule the nucleus in each cell contains so much information.  This information remains inside the cell but the information in them can be copied and carried out of the cell by RNA.  The information in the cell is the genetic code (sequence of nucleotide bases).  The genetic code is written in 3 (base) letter words and every three base word gives instructions to one amino acid.  The words are arranged in certain way so amino acids build into polypeptides which then mature into a protein.  There are 64 different codons (3 letter words) but only 20 different amino acids.  Many different codons encode each amino acid except for the start codon methionine (AUG).  All genes in RNA begin with the start codon methionine (AUG).  Even though there is only one way to start a codon there is three ways to stop (UAA), (UAG), and (UGA). 
Translation occurs in the cytoplasm ribosomes and takes the recipe converting the mRNA into one or more proteins.  So to recap mRNA (messenger) is basically a copy of the “recipe” and tRNA (transfer) are small RNA molecules that are in many different shapes and then escorts amino acids to the ribosome (site of translation).  Ribosomes are made out of ribosomal RNA (rRNA) and protein.  Ribosomes have the enzymes that catalyze the peptide bond formation.  They also contain the sites for mRNA and incoming amino acid tRNA.  The process starts with initiation where the start codon AUG and initiator codon carry tRNA and form a complex.  Next is elongation where tRNA brings specific amino acids to already developing proteins.  The elongation happens when each amino acid is added to the chain.  Last, any of the stop codons UAA, UAG, or UGA are used to terminate the developing chain and the protein is released from the ribosome. 
 A Cell Reproduction: One Cell Becomes Two
Pounds of cells are replaced daily.  Of all these cells there are two types of cell reproduction on humans.  One is the mitotic cell cycle where new diploid cells are generated and contain chromosomes in pairs.  The other generates haploid gametes that contain chromosomes not in pairs called meiotic cell division. 
There are two different periods that occur within the cell cycle.  The mitotic cell cycle lasts for approximately 18-24 hours.  There is a sequence of cell growth phases in order: interphase, prophase, metaphase, anaphase, telophase, and cytokinesis phase.
 Interphase
 Interphase is the cycle that longest has growth period.  Interphase is divided into three categories 1. G1 phase 2 .S phase 3. G2 phase 4. G0.  During the cell cycle the G1 phase is very active and is the primary growth phase.  During the S phase DNA is synthesized for cell division.  The final growth phase before cell division is G2.  Lastly in G0 the cells go through a non-growing, non-dividing state.
 Prophase
 In prophase protein structure called the mitotic spindle is formed.  The nuclear membrane dissolves and metabolic activity decreases so the concentration goes to dividing.  
 Metaphase
In metaphase duplicate chromosomes form a single line at the equator between the centriole poles.  During anaphase duplicate chromosomes separate by popping apart from each other. 
   Telophase
Telophase is when everything returns to normal.  Then in cytokinesis a contractile ring of protein filaments form at the middle of the cell and tighten forming a cleavage furrow.  Two daughter cells are formed as the contractile ring pinches them apart.  Then during the mitotic phase the nucleus and cytoplasm divide during approximately one hour of the cell cycle.  Mitosis (nuclear division) is followed by cytoplasmic division which is cytokinesis.  With the process of cytokinesis daughter cells are formed.  Daughter cells are identical to the parent cells and this cycle repeats over and over.  During mitosis duplicated DNA is distributed.  Then between the two daughter nuclei the nucleus divides. 
Meiotic is the process of two nuclear divisions where the chromosomal material is rearranged and reduced by half during the formation of sperm and eggs.  Daughter cells are haploid because meiosis reduces the chromosome number by half.   Meiotic cell division includes two effective division processes called meiosis l and meiosis ll. Meiotic cell division have four stages: prophase, metaphase, anaphase, and telophase.  In meiosis l the cell goes through S phase where the DNA and all 46 chromosomes are duplicated.  During prophase the duplicated chromosomes pair up and swap gene sections called crossing over.  This then creates a combination of both the person’s parent’s chromosomes. During the rest of meiosis l pairs of chromosomes are separated from each other rather than the duplicates of each pair.  In meiosis ll the chromosomes are not duplicated again.  During meiosis ll the 23 duplicated chromosomes line up and the sister chromatids are separated from each other.  When gene sections swap in meiosis l none of the four haploid daughter cells are exactly alike.  That is why if two people have more than one child each child has some similarities but do not look the same. 
How Cell Reproduction is regulated
Not all cells divide at the same rate as other cells.  Some cells stop dividing after adolescence where other cells divide throughout our lives. A certain protein called cyclic controls the progression of G1, S, and G2 phases through fluctuations in cyclic concentrations.  Cyclic activate certain proteins that start specific events within the cell like DNA replication or the formation of the mitotic spindle.  There are check points at the end of phase G1 and G2 to make sure everything has been completed properly.  Lastly if certain nutrients aren’t available the cell can stop if needed.  Cells also regulate tissue growth and organ size.
                                                                 
Environmental Factors Influence Cell Differentiation
Every cell in our bodies came from a single cell.  Every cell in our bodies has the same genetic code within it.  Why don’t cells all look the same?  Through a process called differentiation cells become different than the original parent cell.  Some cells become skin (epithelial cells), organs, bone and blood to give some examples.  At different stages in our lives cells differentiate expressing different genes.  It is very evident in the beginning of life.  When cells get past the eight cell stage the environment that surrounds the cells becomes different than the environment of the cells surface.  During later stages in our lives differentiation is effected by the local environment and the developmental history of cells. 
Cloning an Organism Requires an Undifferentiated Cell
There are two different techniques for reproductive cloning called embryo splitting and somatic cell nuclear transfer.  In embryo splitting an egg is fertilized in vitro (test tube) and allowed to divide to the eight-cell stage.   At this stage all eight cells can be divided and if placed into women could develop into spring for herd improvement.  In somatic cell nuclear transfer involves creating a clone of an adult organism.  Somatic cells have a full set of DNA instructions.  This technique was used in 1997 when scientist cloned a sheep named Dolly.  The clone of Dolly didn’t live very long making scientists question if the adult cells are already damaged.  The process involves scientists combing a somatic cell from an adult with a fertilized egg that has had the nucleus removed.  The nucleus from the adult somatic cell already contains the instructions for making a copy to clone the adult animal.  The egg is then inserted into a segregate mother enabling it to develop.  The baby will be an exact clone of the adult that it was cloned from.
                                      
Dolly the Sheep
Therapeutic Cloning: Tissues and Organs
Therapeutic cloning is defined as a procedure in which damaged tissues or organs are repaired or replaced with genetically identical cells that originate from undifferentiated stem cells. (http://medical-dictionary.thefreedictionary.com/therapeutic+cloning, accessed 16 Feb 2012) The goal is to be able to take a single cell from one patient and create new tissue or even a new organ for another patient.  This is a way to create new cells without having the risk of tissue rejection.  Although this treatment is a little ways off when it becomes available it will be beneficial to many people.
                                      
Triplet Code
Chapter 18 Cancer
 1 in 3 people will experience cancer in their lifetimes. 
1 in 4 people will die from cancer.
Tumors can be Benign or Cancerous
There are two characteristics of normal cells.  Normal cells remain in one location for their lifetime (except for blood cells).  Normal cells have regulatory mechanisms to keep the rate of cell division in check.   Hyperplasia is when cells increase their division and in some cells hyperplasia is not normal.  These out of control cells then form a mass of cells called a tumor.  Not all tumors are cancers.  If tumors stay in one place the mass of cells are called benign tumors.  These cells still have the same structure as the cells they divided from.   Sometimes benign tumors can turn into something more damaging. 
                                                                    

Cancerous Cells Lose Control of their Functions and Structures
If cells advance to becoming cancer, the cell structure changes.  Abnormal structural changes of a cell are called dysplasia.  Dysplasia is often a sign that tumor cells are precancerous.  The tumor becomes more and more disorganized while cells continue to pile up on each other randomly.   A tumor isn’t defined as cancer until at least some cells lose all aspects of organization, structure, or regulatory control.  Tumors that remain in one place are called in situ cancer and can usually be surgically removed if it is caught early.  If the cancer goes through additional changes then metastasis can result.  Metastasis is the spread of cancer to another organ or place in the body.  This happens when cancer cells break away from the main tumor and get into the blood stream or lymph.  Cancers that metastasize and travel through blood or lymph then invade normal tissue resulting in malignant tumors.  Malignant tumors often grow out of control overrunning tissues and organs.   
How Cancer Develops
For cancer to develop two things have to happen at the same time.  One is the cell has to uncontrollable grow and divide ignoring the signals to stop dividing.  The other is that when cells genes become abnormal and stop functioning correctly the cell goes through physical changes making the cell break away from other cells.  Tumor suppressor genes and pronto-oncogenes normally regulate genes that promote cell growth and division.  When pronto-oncogenes mutate or become damaged, cancer called oncogenes can occur by increasing internal cell growth and division faster than usual.  Another regulating gene that is supposed to stop all unchecked cell growth is the tumor suppressor gene.  When this gene becomes damaged it contributes to cancer because cell activities continue to be unrestricted.  The gene p53 has the primary role to inhibit cell division of cells that already have cancerous features.  When this gene becomes damaged many different cancers can develop.  The last class of gene that contributes to cancer is mutator genes.  These genes are supposed to be involved in DNA repair during the copying process.  When this gene mutates errors are prone to DNA replication causing mutations in other genes at a fast rate. 
The transformation process of a normal cell turning into a cancerous cell is called carcinogenesis.  A carcinogen is any substance or physical factor that causes cancer.  Some viruses and bacteria also contribute to some cancers.  Viruses that contribute to cancer are human papillomavirus, hepatitis B and C, HIV, Epstein-Barr virus, and human T-cell leukemia.  Only 15% of viruses and bacteria account for cancer.  Other things that lead to cancer is environmental chemicals, tobacco, radiation, a person’s diet, and internal factors. 
Advances in Diagnosis Enable Early Detection
Early detection of cancer is important in surviving cancer.  X rays can view tumor masses but isn’t the most effective imaging available.  Other advanced imaging techniques are also used.  PET otherwise known as positron-emission tomography create a 3D image showing metabolic activity in the body.  Another imaging technique is magnetic resonance imaging (MRI) that uses short bursts of a powerful magnetic field to show cross sections of the body.  An MRI can see tumors hidden by bone and between tissues.  Some of these genes have already been identified.  This is very controversial because some diseases have no cure.  Would someone want to know that they had the genetic components to possibly develop a disease without a cure?  Instead of doing genetic testing maybe another test would be better accepted.  There is an enzyme that isn’t usually found in normal cells but is usually found in cancerous cells.  If people were tested for this enzyme cancer could be detected early helping the survival rate.
Cancer Treatments
Cancer is treatable.  There are many variables but with the current treatments available 50% of all cancers are cured.  The current treatments consist of surgery, radiation, and chemotherapy.  Surgery removes tumor masses.  Radiation focuses on a specific area to kill cancer cells.  Chemotherapy puts cytotoxin (cell damaging) chemicals in the body to destroy cancer cells.  Some chemo drugs stop cells from dividing and others interfere with DNA replication.  Drugs designed to stop cell division the effects are nausea, hair loss, anemia, and have a hard time fighting infections.  There are many treatments being developed and are currently in a trial phase.  Vaccines are being created to prevent certain cancers as well.  Cancer requires lots of energy because they are dividing so rapidly.  Researchers are excited about anti-angiogentic drugs that restrict blood vessel growth.  These drugs may be able to “starve” tumors by limiting their blood/nurturance supply. 
The 10 Most Common Cancers
The top ten cancers are skin, lung, breast, prostate, colon/rectum, lymphoma, urinary bladder, kidney, uterus, and leukemia. 
There are three main types of skin cancers with melanoma being the deadliest.  When looking at dark patches of your skin you should evaluate them using the “ABCD” rule.  A: asymmetry meaning the two halves don’t match; B: border meaning to check if there is an irregular shape; C: color watching differences in color or if it is black; D: diameter means to measure and make sure the size is less than a pea.  Other warning signs might be scaliness, itching, oozing, and bleeding.  The other two main skin cancers are basal and squamous cell cancers having a 95% cure rate. 
Skin Cancer
Lung cancer in most cases is preventable.  Smoking is the biggest culprit to lung cancer.  As of now there isn’t screening to detect this cancer early.  Most of the time it is discovered when the cancer is already advanced.  This cancers cure rate isn’t very good with the one year survival rate at 41% and 15% over five years. 
 Lung Cancer
Breast cancer is most common in women but can also occur in men.  Breast cancer is found by self-exams, doctor exams, and mammograms.  Researchers say that age plays a large part in this cancer and the risk increases as someone ages.  There are other risk factors like early menstruation and hormone replacement therapy that can increase someone’s risk for breast cancer.
 Breast Cancer
Men are affected by prostate cancer and the biggest risk is advancing age.  Prostate cancer is generally discovered early with digital rectal exam or by a prostate- specific antigen test.  The survival rate for prostate cancer is up from 25 years ago from 69% to 99%. 
Prostate Cancer
Colon and rectum cancers start in the form of polyps.  These polyps are small benign growths that develop within the colon lining.  Most polyps never become cancerous and if they do become cancerous it takes many years.  The American Cancer Society recommends a colonoscopy every ten years after the age of 50. 
Lymphoma is cancer of lymphoid tissues including Hodgkin’s disease and non-Hodgkin’s lymphoma.  Researchers feel the risk factors for this cancer have to do with a person’s immune system.  Treatments usually involve radiation and chemotherapy. 
 Urinary bladder cancer is treatable with surgery if found early.  Risks of urinary bladder cancer are smoking, living in urban areas, and jobs that expose someone to rubber, leather, and dyes.  Blood in the urine is an important sign to get checked by a doctor.  If caught early the survival rate is between 73-97%.  If the cancer has spread the survival rate drops to only 6%.
The risks of kidney cancer are smoking, heredity, gene mutations, exposure to toxic agents, and age.  The main treatment is to remove the cancerous kidney if the other kidney is in good working condition.  If removing a kidney isn’t an option then radiation and chemotherapy are used.  (Chemotherapy doesn’t usually have any effect)
 Papillary Renal (kidney) Carcinoma (cancer)
Uterine cancer includes cancers of the cervix and endometrium. The main symptom is abnormal bleeding.  Cervical cancer is usually caused by a virus called the human papillomavirus.  A new vaccine is almost 100% effective in blocking strains of this cancer causing virus.  There is a range of risk factors but once again smoking was on top.  The survival rates are high for these cancers with appropriate treatment.

Leukemia is cancer of immature white blood cells in bone marrow.  In advanced stages bone marrow becomes completely filled with cancerous cells.  The cause for leukemia is still unknown but scientists have some ideas.  This cancer affects both adults and children.  The treatment for leukemia is chemotherapy and is then usually followed by a bone morrow transplant.  The chance of survival has increased over the past few years especially in children. 
Most Cancers can be prevented
Most cancers can be prevented.  At least 60% of cancer cases are believed to be caused by smoking and having a poor diet.  Reducing sun exposure greatly reduces the occurrence of skin cancer.  Overall eating a diet high in fruits and veggies, exercising, practicing healthy habits, and avoiding the sun reduce the risk of cancer.  Other things we can do to is to get regular cancer screenings.   We need to be conscious of changes in our skin and any lumps in breast or tentacles.  Knowing your family history allows you to know any genetic defects.  Even though cancer is a scary word we need to be informed about cancer in general.  With diet and exercise the risks of cancer are lowered and above all DO NOT SMOKE!!
                                                    
Chapter 19
Your genotype is the genetic basis of your Phenotype
Humans have 23 pairs of chromosomes which account for 22 pairs of autosomes and 1 pair of sex chromosomes.  An autosome is defined as a chromosome that is not a sex chromosome (http://www.answers.com/topic/autosome, accessed 24 Feb 2012).  Even when autosomes appear identical there can still be slight differences between the pair.  The un-identical produced genes are called alleles.  Because alleles are different they code for different proteins and have a slightly different structure than the original gene.  Sometimes someone will have an identical pair of alleles in their genes called homozygous.  A person with two different alleles of a gene is called heterozygous.
Scientists believe alleles are the result of millions of years of mutation.  These mutations and all the various genes in humans are summed up as the human gene pool.  The uniqueness of each person is due to different alleles in approximately 22,000 genes.  An individual’s set of alleles is called a genotype.  This is better defined as, the combination of alleles located on homologous chromosome that determines a specific characteristic or trait (http://www.answers.com/topic/genotype, accessed 24 Feb 2012). A phenotype is the expression of a trait due to genetic and environmental influences.  This has a great effect on the person’s characteristics called phenotype.  Types of different phenotype traits are a person’s hair color, eye color, skin color, body type, and abilities.  Phenotypes that aren’t physical traits aren’t recognized as easy.  Things like a person’s blood type and susceptibilities to disease have to be tested for.   A person’s genetics account for many health factors but not all of them.  The lifestyle someone chooses to live also plays a big part in the person’s life.
Genetic Inheritance Follows Certain Patterns
Alleles are assigned uppercase and lowercase letters to help researchers document them.  People who have the same two alleles of a gene are homozygous and people with different alleles are heterozygous.  A punnett square is a square used in genetics to calculate the frequencies of the different genotypes and phenotypes among the offspring of a cross (http://www.merriam-webster.com/dictionary/punnett%20square, accessed 24 Feb 2012).  

This is a simple way to show all the patterns of possible inherited alleles in a particular genotype.  Gregor Mendel was an educated monk from the 1800’s.  Through the use of plants he figured out genetics and how traits are passed from parents to their children.   One experiment Mendel preformed was to see if breeding a yellow pea plant with a green pea plant produced yellow or green peas.  He found they only produced yellow peas but when two pea plants with a recessive green gene were bred that the plants produced mostly yellow peas but some green peas (75/25). 
Gamets are haploid with half the number of chromosomes and genes of each parent.  In the law of segregation the allele that a parent contributes to a gamet is done randomly.  A heterozygous parent has a 50% chance of donating a specific allele to each gamet.  One neat example is a person’s hairline.  A person’s hairline is controlled by a single gene with two alleles.  One allele controls if someone has a widow’s peak and the other controls a straight hairline.  This is a major reason why variation exists in people and also a reason why traits can skip a generation.  Dominant is defined as designating an allele that does not produce a characteristic effect when present with a dominant allele or relating to a trait that is expressed only when the determining allele is present in the homozygous condition (http://www.thefreedictionary.com/recessive, accessed 25 Feb 2012).  Dominant is then defined as an allele of a gene pair that masks the effect of the other when both are present in the same cell or organism (http://www.definitions.net/definition/Dominant, accessed 25 Feb 2012).  Most recessive alleles don’t have an advantage or disadvantage to the homozygous recessive person.  The alleles that effect appearance stay in the gene pool because they don’t harm anyone.  On the other hand alleles that are harmful in the human population are kept in check by homozygous recessives dying out early, where harmful alleles in a heterozygous population survive.  Dominant alleles don’t mean a specific trait is guaranteed.  In fact I learned some dominant traits are actually very rare even though they are dominant.  How a dominant allele works has to do with the combination of recessive and dominant heterozygotes.  With the use of a punnett square a person can map the probability of certain traits.
Other Dominance Patterns
One of Gregor Mendel's great discoveries was the Principle of Dominance and part of his discovery was incomplete dominance.  Gregor Mendel (July 20, 1822 – January 6, 1884) was an Austrian monk whose studies of the inheritance of traits in pea plants helped to lay the foundation for the later development of the field of genetics (http://www.newworldencyclopedia.org/entry/Gregor_Mendel, accessed 6 March 2012).
 Gregor Mendel
Sometimes alleles aren’t recessive or dominant instead they are of incomplete dominance.  This is stated as heterozygous genotype results in a phenotype that is halfway between the two homozygous phenotypes.  This creates a phenomenon of whether a person has the trait of curly, straight, or wavy hair. 
Co-dominance is when both alleles are expressed the same.  An example of co-dominance is sickle cell anemia where hemoglobin in red blood cells crystalize in lower oxygen levels.  In result the red blood cells have a crescent shape and are delicate.  In sickle cell anemia the odd shaped red blood cells clog blood vessels restricting oxygenated blood flow.  This is due to one of two alleles involved in hemoglobin making in red blood cells.  People homozygous for sickle cell anemia rarely live into their thirties.  Heterozygous people who carry the trait have equal amounts of each type of hemoglobin.  These people might feel some minor effects but usually do not.
Other Factors Influence Inheritance Patterns and Phenotype
Only three genes control a person’s eye color.  Many traits are not due to one pair of genes but many genes act together at the same time called polygenic inheritance.  An example of polygenic inheritance is a person’s height, body size, and shape.  The combination of alleles determines whether or not a person will be tall, short, big, small, ect.  Other conditions influenced by polygenic inheritance researchers are starting to understand including cancer and heart disease. 
Environmental influences and our genotype are determined by phenotype.  People in developed countries tend to be larger than people in less developed countries.  This has happened in too short of time for genetics to only contribute to people getting larger so quick.  Environmental impact also contributes to people getting larger quickly, affecting the gene pool.  People’s actions and the risks they take with their health play a huge part in whether a disease will actually develop.  Knowing your family history is important to be aware of because a person can better protect themselves by their actions.  Huntington’s disease is the exception to this and is always fatal. 
Many alleles are inherited together because they are joined on the same chromosome.  These alleles are called linked alleles.  During the reshuffling of alleles across each pair of autosomes during meiosis sometimes linked alleles are not inherited together.  Genetic variability is a result of the assortment of alleles on different chromosomes, shuffling are of linked alleles crossing over between autosomes, and the random fertilization of an egg by sperm. 
Sex-linked Inheritance: X and Y Chromosomes Carry Different Genes
Chromosomes can be identified in cells only just before cell division.  This exhibits all the chromosomes of an organism called a karyotype.  A human karyotype has 22 matching chromosomes and one pair of sex chromosomes.
Karyotype
(http://www.ds-health.com/trisomy.htm, accessed 26 Feb 2012) The mother/woman has two X chromosomes in which one X is donated to her offspring.  The father has one X chromosome and one Y chromosome in which one is donated to offspring.  If the father donates a Y chromosome the baby will be a boy and if an X chromosome is donated then the baby will be a girl. 
The father determines the sex of all fertilized eggs.  Women have a double X sex chromosome that is a homologous pair.  Males don’t have this because they contain an X and Y causing a greater risk for diseases associated with the recessive alleles on the male’s sex chromosome.   The inheritance patterns on genes located on sex chromosomes is called sex-linked inheritance.  Genes on the Y chromosome influence differences in male organs, production of sperm, and the development of secondary sex -characteristics.  Where in the females X chromosome genes act like paired genes.  Hemophilia is a sex-linked inheritance from the X chromosome.  Hemophilia is better known as “bleeder’s disease” and is a lack in blood clotting.   This disease is more common in males than females because females inherit one normal allele so she remains a disease carrier.  If the father is a carrier only his daughters will be carriers.  If the mother is a carrier then all her sons will be carriers.  Almost all X linked diseases are caused by recessive alleles not dominant alleles.
Some non sex genes in the 22 remaining chromosomes influence different traits. For instance the allele that causes baldness can be in both men and women.  The baldness allele is recessive in women but men become bald even when baldness is heterozygous.  The difference between men and women has to do with testosterone.  Influences by genes on sex chromosomes can convert recessive genes into dominant genes.
Chromosomes May be Altered in Number or Structure
Most embryos die before anyone is aware of them if they have errors or missing chromosomes.  Failure of homologous chromosomes or sister chromatids to split correctly is called nondisjunction.  During meiosis when sister chromatids don’t separate correctly the result is a change in the chromosome number of sperm or egg cells.  The mishaps during meiosis are very detrimental because they can alter the development of the entire being.  If a mishap happens during mitosis then the two daughter cells usually die and new cells replace the two damaged ones.  Problems that happen during mitosis aren’t nearly as serious as problems that occur during meiosis. 
Sometimes chromosome number alterations don’t make the embryo die.  Some babies are born with altered chromosomal numbers.  The most common chromosome number alterations are Down syndrome.  The most common type of Down syndrome is when the baby is born with three copies of chromosome number 21.  One in 1,000babies is born with Down syndrome. 

(http://www.ds-health.com/trisomy.htm, accessed 26 Feb 2012)
 The likelihood of a baby born with Down syndrome increases with how old the mother is when the baby is born.  Mothers under the age of thirty have a one and 1,300 chance of having a baby with Down syndrome where mothers who are forty have a one in 100 chance.  Then when mothers are 45 the probability of having a baby with Down syndrome rises to one in 25.  There is a test called an amniocentesis where amniotic fluid is tested to detect any chromosomal abnormalities. 
Alterations in sex chromosomes can also produce different syndromes.  In Jacob syndrome a male has one X and two Y chromosomes.  The men with this syndrome tend to be tall and can have some mental impairment.
Kline Felter syndrome
( http://images.search.yahoo.com/images/, accessed Feb 27 2012)  Kline Felter syndrome is males having two X and one Y chromosomes.  They are also usually tall and have mild mental impairment.  They are sterile and may develop breasts because of the extra X chromosome.  The syndrome called Trisomy-X means a woman has three X chromosomes.  Women who have this syndrome usually have no effects except for the possibility of mild retardation. 

 Turner syndrome is rare because usually the embryo aborts before the baby is born.  People with this syndrome are female and only have one X chromosome.  They are sterile and their bodies look childlike but besides that there aren’t any mental problems. 
There are other chromosomal problems can occur besides extra chromosomes.  In deletion, a piece of a chromosome breaks off and is lost.   When deletion happens the egg, sperm or embryo all die.  Babies that are born without a specific chromosome result in mental and physical retardation.  Sometimes a piece of a chromosome breaks off but reattaches on a different place either on that chromosome or a different chromosome called translocation.  Even though all the genes are still present the order isn’t correct.  This results in slight changes in gene expression like the increased chance of certain cancers.
Many Inherited Genetic Disorders Involve Recessive Alleles
The expression of inherits genetic disorders only happen if a person inherits two defective alleles.  If a parent is the carrier of a defective allele but has one correct allele then that parent will remain only a carrier.  The parent has the possibility of passing defective alleles to their children.  Sometimes more than one gene pair causes a disease.  Enzyme deficiencies are caused by a specific gene on a chromosome.  The combination creates sometimes rare and deadly diseases.  Tests are available to determine anyone who is a carrier of these diseases.  The most well-known of these diseases is Huntington’s disease.  Huntington’s affects people who carry this dominant allele.  They show symptoms in their 30’s and are usually dead by the time they are 50.  It’s a very cruel disease that causes a lot of suffering.  There is genetic testing for Huntington’s and other inherited disorders.  Scientists are working intensely to identify all 22,000 genes responsible for increasing the chances of breast cancer, skin cancer, and osteoporosis.  Preventing and treating these genetic diseases is greatly researched, especially with new technology being invented.  
Genes Code for Proteins, not for Specific Behaviors
To become a human being a specific set of instructions have to be precisely carried out.  Genes represent the set of instructions needed and can determine a person’s unique physical traits.  Genes code for specific proteins that give a person curly, hair or different mood tendencies.  Genes can’t be blamed for the bad or good things people do.  Proteins make up many structures within cells and control a cells function.  Together genes and their proteins can influence a person’s mood and other tendencies.  But there isn’t any evidence that a specific gene causes happiness or depression. 
Chapter 20
DNA Sequencing Reveals Structure of DNA
Biotechnology is biological knowledge that is used for human purposes.  Recombinant DNA is defined as genetically engineered DNA prepared by transplanting or splicing genes from one species into the cells of a host organism of a different species. Such DNA becomes part of the host's genetic makeup and is replicated (http://www.answers.com/topic/recombinant-dna, accessed 9 March 2012).  Genetic engineering is the manipulation of the genetic makeup of cells or an entire organism.  Genetic engineering holds a lot of promise for the future but is still very new. Determining the precise sequence of base pairs that make up the individual DNA strands can be done.  First scientists put millions of identical copies of a single strand of DNA to be sequenced in a test tube.  Then short strands DNA called primers are added, whose job is to bind to each one of the ends of the DNA.   It is the starting point of DNA and synthesizes a new complimentary DNA strand.  Next the nucleotides are put in the mix and an enzyme is added called DNA polymerase that helps the nucleotides to create the growing strand.  Synthesis of DNA has then begun.  Using a process called gel electrophoresis; an electrical field causes the DNA pieces to navigate through the gel.  (This is done on a flat surface)  The single strand sequence of DNA is complimentary to the original DNA fragments. 
DNA can be cloned in the Laboratory
Recombinant DNA is a different process when dealing with plants and animals.  With the ability to recombine DNA has the ability for scientists to create organisms that have never been created before.  Recombinant DNA also has the ability to fix defective human genes.  Recombinant DNA technology is the process of cutting, slicing, and copying DNA and the genes it holds.  Recombinant DNA technology needs special components and tools including restrictive enzymes are enzymes that naturally occur in some bacterias.  This is done by breaking the bonds between the base pairs in DNA.  In nature these enzymes cut up any raiding viruses.  The most useful cut is in a palindromic DNA sequence leaving two complimentary short, single strands of DNA that are complimentary to any other DNA containing the same enzyme.  DNA ligases are enzymes that bind DNA fragments back together after a restricting enzyme has cut them apart.  Plasmids are important and are self-replicating DNA molecules that are found in bacteria.  Plasmids are round and small.  They aren’t a natural part of bacterial chromosomes but are very important in non-normal gene replication done in labs. 
The technique for producing cloned genes with recombinant DNA includes 1. Isolating DNA plasmids and the human DNA of interest 2. Cutting both DNA’s with the same restricting enzyme 3. Mixing the DNA fragments with the cut plasmids 4.  Add DNA ligase to complete the connections 5. Introducing the new plasmids into bacteria 6. Select the bacteria containing the gene of interest and allowing them to reproduce.  This technique can create endless amounts of a precise protein.
Another way to clone DNA is through polymerase chain reaction.  This technique is fast using small pieces of DNA and makes millions of copies of the DNA.  This is done by heating the piece of DNA to unwind it.  Then they are mixed with complimentary primers.  Next nucleotides are added that are important in creating new DNA strands.  Lastly DNA polymerase is added creating the enzyme to catalyze and attach the nucleotides to the growing DNA strands.  Heating and cooling set the strands and after 20 times there is over a million identical DNA copies (clones).  

(http://images.search.yahoo.com/image, accessed 10 March 2012)
Sometimes DNA needs to be identified when someone doesn’t know where it came from.  This technique is used mostly at crime scenes.  It is used to figure out who an unknown deceased person’s identity is, who the father of a baby is, and to trace someone’s ancestry.  This technique allows someone to identify the source of DNA after it has been adequately copied by the polymerase chain reaction.  Then restriction enzymes are used to cut the DNA into pieces.  Next he DNA is places in gel that separates them according to size.  A printout of DNA fragments on the gel is called electropherogram or DNA fingerprint. 
Genetic Engineering Creates Transgenic Organisms
Genetic engineering is the ability to produce transgenic organisms that can transfer one or more different species of genes to create many new possibilities.  There are many uses for transgenic bacteria.   They help to produce or replace hormones in the body that aren’t being produced with proteins.  When a person is missing a certain hormone it can be life threatening.  One instance of this is insulin and if the body doesn’t produce it and the hormone isn’t being replaced the person won’t survive.  There are also non hormones that are created such as tissue plasminogen activator that prevents or reverses blood clots.  Another use for transgenic bacteria is the production of vaccines.  I learned that vaccines are usually made from dead or weak organisms that actually cause the disease.  I also learned that sometimes vaccines can actually give you the disease they are trying to protect you from.  The reason why some vaccines are expensive or limited is because the organisms that cause a disease evolve.  Sometimes vaccines have to be reworked yearly.  Lots of time is spent trying to make successful vaccines.  Other uses that are cleaning up toxic waste and oil pollutants, removing sulfur from coal, making citric acid, and making ethanol. 
Transgenic plants aren’t as easy to make but hold a lot of promise.  One way of changing plants DNA is by shooting recombinant DNA into plant cells at high velocity.  Another way is by shocking plants at high voltage in the presence of recombinant DNA or by putting infected bacterium with DNA that then infects the plant.  Some plants then may incorporate the new DNA into the original plant DNA creating new traits in the plant.  One plant that genetic engineering has been so successful with is tomatoes.  Tomato plants can now resist freezing, have a longer shelf life, and resists pests.  Other benefits of genetic engineering are larger leaves to aid in photosynthesis, better roots to fight drought, and plants that mature earlier to yield more food.  One thing I found disturbing was the information on edible vaccines.  They have made a Hepatitis B vaccine produced in raw potatoes and are working on many vaccines to be produced in bananas.  In some ways I understand especially for third world countries but I question if this is truly safe without any side effects.

(http://images.search.yahoo.com/images, accessed 9 March 2012)
Even harder to produce than transgenic plants is transgenic animals.  This is because the numbers of eggs available are limited and only 10% of eggs combine recombinant DNA on their own.   The process begins with inserting DNA into already fertilized eggs.  Even though there are some difficulties with transgenic animals new advances are happening.  One way is with growth hormone, one in particular is   Bovine growth hormone that makes animals grow faster and larger which some people are uneasy about. 
Gene Therapy: The Hope of the Future?
Gene therapy is when human genes are inserted into human cells to treat or correct a disease.  There have already been exact gene mutations found on specific chromosomes that cause many genetic problems.  Researchers hope that in the future these problems could be fixed with gene therapy.  One problem is that in adults some genes have already mutated through the DNA replication process.  Replacing a missing gene might seem difficult but is being researched.  Also the question is if the offspring of a person who received gene therapy would still inherit the mutation. 
It isn’t necessary to replace a missing gene into all the cells.  Rather if an adequate number of new genes were replaced so enough of the missing protein was produced preventing the disease.  One way of doing this is through vectors (transporters) that deliver genes into cells.  The best vectors are viruses called retroviruses.  The retroviruses splice their own RNA based genetic code permanently into the DNA they infect.  Another way is by taking tissue from the body and exposing it to the retrovirus then returning it to the body.  Researchers then hope the cells will then integrate the genes back to where the tissue was taken from.  There are some drawbacks to retroviruses and many techniques are still very experimental. 
There are successful gene therapy stories and treatment is helping people.  Some people with conditions that have immune system deficiencies are susceptible to infections.  But now with gene therapy treatment people can live better lives.  Cancer may also be treated with gene therapy soon.  There are many different approaches being researched and tested to treat cancers.  The future will hold many new breakthroughs in our lifetime. 

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