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UNC-Chapel Hill BIOL 101 - Chapter 14- Mendal and The Gene Idea

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I. Gregor Mendel’s DiscoveriesBreeded garden peas for heredity experimentA. Experimental and Quantitative Approach1865: The Father of Genetics. Influences physicist Doppler and botanist Unger. Helped spark interest in gene variation. Total control over mating between flowers. flowers self-fertilize naturally. Believed not medium between purple and white “either-or” situation. Focused on other aspects of plants, such as seed weight etc. This helped discover inheritance. true-breeding parents considered P generation. first filial generation or the hybrid offspring are called F1 .second filial generation is called the F2. F2 determined fundamental principles for heredity.● character: heritable feature, such as flower color in garden peas, that varies● trait: each variety for a flower color, such as purple and white● true-breeding: when self-fertilize produce same variety● hybridization: crossing of two true-breeding varietiesB. The Law of Segregationa. Allele pairs separate during gamete formation and randomly reform as pairs during the fusion of gametes at fertilization.1. Different Alleles cause the varied flower colors in the pea plants. The gene is located on a specific locus on a specific chromosome. On each chromosome, the DNA for flower color is located in the same spot, but the bases used to represent the trait may be different since the traits are different.2. For each character, an organism inherits one from each parent, which may be the same or differ.3. When alleles differ, one is dominant and fully expressed in appearance. The other is recessive and is not noticeable in appearance.4. Two alleles segregate during gamete production, if each gamete receives the same allele the parent is true-breeding. if not the hybrids will have a 50-50 chance of either trait.b. Useful Vocabulary1. homozygous: identical alleles for a character (PP/ pp)2. heterozygous: two different alleles (Pp)3. genotype: genetic makeup4. phenotype: physical traits5. Punnett Square: a way of predicting the results of a genetic cross of a known genotypec. The TestcrossBreeding of a recessive homozygote with a dominant phenotype, known genotypeC. The Law of Independent Assortmenta. Each allele pair separate independently during gamete formation when genes for two different characteristics are located on different pairs of homologous chromosomes.1. monohybrids: F1 hybrids in which one follows only one character (Rr)2. dihybrids: heterozygous for both characters (RrPp)D. Rules of Probabilitya. The Rule of Multiplicationb. The Rule of Additionc. Solving Genetic ProblemsE. Behavior of a GeneII. Extended Mendelian DiscoveriesA. Relationship Between Genotype and Phenotypea. Incomplete DominanceThe two genes mix because neither is dominant or recessive. Therefore, both traits show up in the F1 generation as combination or intermediate trait. Ex. a red flower and a white flower produce a pink flower instead of just red and white flowers.b. Dominant AlleleDominance can occur in either a heterozygote or a dominant homozygote. They do not cover one another up in the process of developing a phenotype. Majority of the population has the recessive gene for number of finger, which is 5. In codominance, both genes are present in the phenotype. As in blood, there are three types -- A, B, and AB. The phenotypes of both A and B are present in AB, not mixed or changed in any way. c. Multiple AllelesBlood can has three genes that can make up four phenotypes -- A, B, AB, and O. O type blood being the recessive gene is represented by the ii. There are antigens (antibodies) present in A and B blood that is not present in O. Leaving it impossible to give an O patient blood other than O.IAi, IAIA, IBi, IBIB, IAIB, ii. d. PleiotrophyA gene can affect more than one phenotypic effects. Pleiotropic alleles mostly affect hereditary diseases, such as sickle cell.e. EpistasisOne gene alters the expression of another gene that was inherited independently.f. Polygenic InheritanceAn additive effect of two or more gene loci on a single phenotype.1. Quantitative Characters: A heritable feature in a population that varies continuously as a result of environmental influences and polygenic inheritance.g. Environmental Impact on Phenotype1. Norm of Reaction: range of possibilities for a single genotype, as influenced by the environment2. Multifactorial: phenotype influenced by many factors including genes and environmental attributesh. Heredity and VariationIII. Mendelian Inheritance In HumansA. Pedigree AnalysisA pedigree is a type of family tree where traits are followed from one generation to the next to analysis each dominant and recessive gene. Predictions can be made by examining a pedigree. Since a generation in a human family is about twenty years, a pedigree has to include much of the past to make an accurate model.B. Human Disordersa. Recessively Inherited DisordersThese disorders are represented by aa versus a person lacking the disease is Aa or AA. People who are Aa for a recessive gene are called carriers because they are likely to give that particular gene to their offspring. 1. Cystic Fibrosis: mucus accumulation in the lungs, pancreas, digestive tract, and other organs. Immune cells come to rescue, but contribute to the buildup of mucus.2. Tay-Sachs Disease: a child has a dysfunctional enzyme that fails to break down brain lipids of a certain class causing accumulation in the brain. Eventually causing death usually before four years of age.3. Sickle-Cell Anemia: the person has defective red blood cells and under extreme stress will not carry oxygen properly causing them to form sickle shapes.b. Dominantly Inherited Disorders1. Achondroplasia: a type dwarfism where a heterozygous people will have the phenotype because the gene is dominant.2. Huntington’s Disease: a fatal disease that destroys the nervous system, but shows no signs until the mid 30s to mid 40s.c. Multifactorial DisordersC. Technologya. Carrier RecognitionBy taking various test, heterozygous carriers can be distinguished from dominant homozygotes. For disease such as Tay-Sachs, Sickle-Cell, and Cystic Fibrosis. Carriers have the potential to give the recessive trait to their offspring increasing their chances of acquiring a fatal recessive disease.b. Fetal Testing1. Amniocentesis: During development, a doctor can check for acquirement of a disease by inserting a long needle and extracting amniotic fluid for a karyotype. This takes several weeks to


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UNC-Chapel Hill BIOL 101 - Chapter 14- Mendal and The Gene Idea

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