Ap Bio Diseases Research Essay Example for Free

Ap Bio Diseases Research Essay 1. Norm of reaction: the phenotypic range that a genotype is associated with due to environmental influences. 2. Multifactorial: characters that have many factors, both genetic and environmental, collectively influence phenotype. 3. Pleiotropy: when a gene controls multiple phenotypic effects 4. Epistasis: When a gene at one locus alters the phenotypic expression of a gene at a second locus 5. Carrier: a person who is heterozygous for a recessive disease and therefore does not display the phenotype (disease). They are called carriers because although they are phenotypically normal with regard to the disorder, they can transmit the recessive allele to their offspring. They are heterozygotes and normal (Rr) DISEASES a. Recessively Inherited Disorders Tay-Sachs disease * Inherited disorder in humans where the brain cells of a child with the disease cannot metabolize certain lipids because a crucial enzyme does not working properly. * As the lipids accumulate in the brain cell, the child beings to suffer seizures, blindness, and degeneration of motor mental performance and dies within a few years. * Only children who inherit two copies of Tay-Sachs allele (HOMOZYGOUS) have the disease. Therefore at the organismal level, the Tay Sachs allele qualifies as recessive * The intermediate phenotype observed at the biochemical level is characteristic of incomplete dominance of either allele * At the molecular level, the normal allele and the Tay-Sachs allele are codominant because a person heterozygous for Tay Sachs disease does not have the disease symptoms, but the individual still produces equal number of normal and dysfunctional enzyme molecules Cystic Fibrosis * Most common lethal genetic disease in the U.S, strikes one out of every 2,500 people of European descent. * The normal allele for this gene codes for a membrane protein that functions in the transport of chloride ions between certain cells and the extracellular fluids. * A person who has the disease has two recessive alleles. * Two recessive alleles result in defective chloride transport channels in their plasma membrane. * Therefore they have a high conc. Of extracellular chloride which makes mucus thicker and sticker and it builds up in the pancreas, lungs, digestive tract, etc. leading to multiple (pleiotropic) effects. This includes poor absorption of nutrients from intestines, chronic bronchitis, recurrent bacterial infections, and disablement of a natural antibiotic made by some body cells. Sickle-Cell Disease * Most common inherited disorder among people of African descent, affects 1/400 of A.A. * Caused by the substitution of a single amino acid in the hemoglobin protein of red blood cells. * A person with the disease has 2 recessive alleles. * When the O2 content of an affected person’s blood is low, the sickle cell hemoglobin molecules aggregate into long rods that dorm the normal circular red blood cells in a shriveled sickle shape. * Sickled cells can clump blood vessels which = physical weakness, pain, organ damage, and even paralysis. * The multiple effects of a two recessive sickle-cell allele are another example of pleiotropy. * At the organismal level, the normal allele is incompletely dominant to the sickle-cell allele. * Heterozygotes of the Sick Cell disease have one sickle-cell allele and another normal allele. They are said to have the sickle-cell trait * Heterozygotes of the disease have a single copy of the sickle cell allele, and it reduces the frequency and severity of malaria attacks, especially among young children. * Therefore, about 1/10 A.A have the sickle cell trait because in tropical Africa, where infection with malaria parasite is common, the sickle-cell allele is more common as well because A.A’s with the sickle cell trait have a higher survival rate. * The presence of heterozygous amounts of sickle-cell hemoglobin results in lower parasite densities in the body! b. Dominant Inherited Disorders Achondroplasia * A form of dwarfism that occurs in one of every 250,000 people. Heterozygous individuals have the dwarf phenotype. * Everyone who is not an achondroplastic dwarf (99.99%) is homozygous for the RECESSIVE allele. * Dominant alleles that cause a lethal disease are much less common than recessive alleles that cause diseases. * If a lethal dominant allele causes the death of an offspring before they reproduce, the allele will not be passed on to future generations. A lethal recessive allele can be preserved from generation to generation by heterozygous carriers who have normal phenotypes). Huntington’s disease * A lethal dominant allele can escape elimination if it causes death only after an individual who carries the allele has reaches an advanced age. The individual w/ the disease could have already had children and given it to them, like the Huntington’s disease. * A degenerative disease of the nervous system that is caused by a lethal dominant allele that has no obvious phenotypic effect until the person is about 35-40 years old. * Deterioration of the nervous system is irreversible and inevitably fatal. * Affects 1/10,000 in the US * In modern tech, we can analyze DNA samples with a background of the disorder and track the Huntington’s allele to a locus near the tip of chromosome 4. YAY CHAPTER 15 Fruit Fly Lab * Thomas Hunt Morgan picked a species of fruit fly, Drosophila melanogaster for his work. * Fruit flies only have 4 fairs of chromosomes that are easily distinguishable w/ a light microscope. * They can breed really fast. * He found a mutation after a long time; a male fruit fly with MUTANT TYPE eyes: White eyes * Regular fruit flies have red eyes, called the WILD TYP * Wild Type: Trait that is common and is dominant * Mutant Type: Trait that is less common and recessive * Notation for the first mutant (non-wild type) had the subscript w. A superscript + identifies the wild type trait: w+. So all wild type traits (normal have a plus symbol and all mutant’s had no plus signs. * Only males had white eyes in the F2 generation so he concluded that a fly’s eye color was linked to its sex. * Concluded that the gene for white eye mutation was located only on the X chromosome and not on the Y chromosome because males only need one X to have the mutation. A female in the F2 generationw would need two X chromosomes with the recessive mutant allele (w) which was impossible because the F1 father had red eyes. SEX-LINKED GENES AND DISEASES a. Sex linked Gene: * A sex-linked gene is a gene that is located on either sex chromosome X or Y. The term has historically referred specifically to a gene on the X chromosomes. * Fathers can pass sex-linked alleles to all their daughters but to none of their sons (since the father HAD TO HAVE contributed a Y chromosome to make the child a son, then the X must come from the mother and therefore if the disease was on his X chromosome, it wouldn’t have passed on to his son). * Mothers can pass sex-linked alleles to both sons and daughters. * IF a sex-linked trait is due to a RECCESSIVE allele, a girl will only express the phenotype if and only if she is a homozygote. * For males, the term hemizygous is used since they only have ONE x and ONE y. Any male receiving the recessive allele from his mother will ALWAYS express the trait. Therefore more men than females have sex-linked recessive. b. Sex-Linked Diseases 1. Colorblindness Usually rare 2. Duchenne Muscular Dystrophy Affects about 1/3500 males born in the U.S. Characterized by a progressive weakening of the muscles and loss of coordination. Affected individuals rarely live past their early 20’s. The disorder is caused by the absence of a key muscle protein called dystrophin. Scientists have mapped the gene for this protein to a specific locus on the X chromosome. 3. Hemophilia Sex-linked recessive disorder defined by the absence of one or more of the proteins required for blood clotting. When a person w/ hemophilia is injured, bleeding is prolonged because a firm clot is slow to form. People with the disease are treated with injections of the missing protein. LINKED GENES * Linked genes are genes located on the same chromosome that tend to be inherited together in genetic crosses. * An example of a two linked genes on fruit flies is the gene for body type and wings. * In the fruit fly, the WILD (Normal) type for body color is GRAY and for wings are NORMAL wings. * In the fruit fly, the MUTANT type for body color is BLACK and for wings are VESTIGIAL wings. * In his experiment, if genes are located on different chromosomes, then the numbers for Gray-normal, Black-vestigial, Gray-Vestigial, and Black-Normal would be the same, but the #’s of the offspring are different because the genes are located on the same chromosome and the parent alleles are always inherited together. MAPS A genetic map is an order list of the genetic loci along a particular chromosome. * The father apart two genes are, the higher the probability that a crossover will occur between them and therefore the higher the recombination frequency. * So the greater the distance between two genes, the more points there are between them where crossing over can occur. A linkage map is a genetic map based on the recombination frequencies. Map Units are equivalent to a 1% recombination frequency. * So if the recombinant frequency is 17%, then the map unit would be 17. DISEASES DUE TO CHROMOSOMAL ALTERATIONS * NONDISJUNCTIO is when members of a pair of homologous chromosomes do not move apart properly during meiosis I or meiosis II. * ANEUPLIDY is when a zygote has an abnormal number of a chromosome. The zygote can be monosomic (missing one chromosome so it only has 1 chromosome) or trisomic (has an extra chromosome, so 3 chromosomes) * POLYPLOIDY is when organisms have more than two complete chromosome sets in all somatic cells. Down Syndrome (Trisomy 21) * An aneuploidy condition that affects around 1/700 children born in the U.S. * Usually the result of an extra chromosome 21, therefore each body cell has a total of 47 chromosomes * Includes characteristic facial features, short stature, heart defects, respiratory infection, and mental retardation. * Individuals w/ the disease are prone to developing leukemia and Alzheimer’s disease. * On average, people/ D.S have a life span shorter than normal and are sexually underdeveloped and sterile. * Frequency of Down syndrome increases w/ the age of the mother. * The extra chromosome can result from nondisjunction during meiosis I, and some research points to an age-dependent abnormality in a meiosis checkpoint that normally delays anaphase until all the kinetochores are attached to the spindle fiber (Like the M phase in the mitotic cell cycle). Klinefelter Syndrome * When an extra X chromosome is in a male, producing XXY. * Occurs about 1/2000 births. * People w/ the syndrome have male sex organs, but the testes are abnormally small and the man is sterile. * Even though the extra X is inactivated as Barr bodies in somatic cells, they can have some breast enlargement and other female body characteristics. They can also have subnormal intelligence. * Men with the disease tend to be taller than average Trisomy X * When a female has three X’s (XXX). * Occurs about 1/1000 live births * The females are healthy and cannot be distinguished from normal XX females except by karyotype. Turner Syndrome * Monosomy X, only one X in females * Occurs about 1/5000 births * Is the only known viable monosomy in humans * Although these X0 individuals are phenotypically female, they are sterile because their sex organs do not mature. * Most w/ the syndrome have normal intelligence. * When females that have Turner Syndrome are provided w/estrogen replacement therapy, they can develop secondary sex characteristics. Cri Du Chat (â€Å"cry of the cat†) * A disorder caused by a specific deletion in chromosome 5. * A child born w/ this syndrome is mentally retarded, has a small head w/ unusual facial features, and has a cry that sounds like the mewing of a distressed cat. * People w/ the disease usually die in infancy or early childhood. Chronic Myelogenous Leukemia (CML) * A disorder that occurs when a reciprocal translocation happens during mitosis of cells that will become white blood cells. * The exchange of a large portion of chromosome 22 w/ a small fragment from a tip of chromosome 9 produces a much shortened, easily recognized chromosome 22, called the Philadelphia chromosome. MITOCHONDRIAL DISEASES * They reduce the amount of ATP the cell can make. * RARE human disorders. * Mitochondrial mutations inherited from a person’s mother can contribute to some cases of diabetes, heart disease, and Alzheimer’s disease. Mitochondrial Myopathy * Causes weakness, intolerance of exercise, and muscle deterioration Leber’s Hereditary Optic Neuropathy * Can produce sudden blindness in people as young as in their 20s or 30s * 4 mutations found so far to cause this disorder affect oxidative phosphorylation during cellular respiration ANOTHER DISORDER Phenylketonuria (PKU) * Recessively inherited disorder that occurs about 1/10,000-15,000 births in the U.S. * Children w/ disease can’t properly metabolize the amino acid phenylalanine. * The compound and its by-product, phenylpyruvate, can accumulate to toxic levels in the blood, causing mental retardation.