UD BISC 207 - Chapter 16 – Mendelian Genetics

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Chapter 16 – Mendelian GeneticsPart AI. Introduction to Mendel’s Experiments A. Studied trait inheritanceB. “Blended Inheritance” was the popular idea at the time1. Offspring were “averages” of their parentsa. Tall father + short mother = medium childrenb. Their children would pass on the trait of medium height to their offspringC. Mendel’s Model System: peas1. Normally self-fertilize2. Used true-breeding plants that when self-fertilized produced offspring with consistent traits3. Focused on 7 traits, 2 variants of each one4. Cross-fertilized his variants D. Single-Factor Cross: focuses on 1 trait1. P = parental2. F1 = first filial generation (offspring of P cross)a. Offspring are monohybrids3. F2 generation: offspring of F1 crossE. Plant height experiment1. P generation (true-breeding): tall x shorta. “True breeding” = TT x ttb. Based on theories at the time, experiment should yield medium plants but produces all tallc. F1 is not true breeding2. “P” = TT & tt plants3. F1 = Tt plants produced from P crossT Tt Tt Ttt Tt TtT tT TT Ttt Tt tt4. Tt = heterozygous; TT = homozygous dominant; tt = homozygous recessive5. Data supports particulate inheritancea. Offspring inherit traits as unchanging, discrete hereditary units (genes)II. Genes come in different forms: Alleles A. Dominant/recessive1. Incomplete dominance: cases where 2 alleles, if both present, both contribute to phenotypeB. Location of Gene on chromosomes is its locus C. Principle of Segregation: alleles are separated during gamete formation (fig. 16.9)F1 cross (Tt x Tt)P cross (true breeding; TT x tt)1.III. Test Cross A. Cross to determine genotype of an unknownB. Crosses unknown genotype with a homozygous recessive (aa) individual to reveal the unknown genotype, based on resulting plants1. Ex. Cross an unknown tall plant (Could be TT or Tt) with a tta. If some of the F1 plants are short, unknown parent is Ttb. If all F1 plants are tall, unknown parent is TTPart BI. Predicting Trait Inheritance Patterns (Probability Rules) A. Product Rule1. If 2 or more independent events need to occur, probability of both happening is the product of each one’s individual probability2. Ex. Tossing a coin: probability it will land on heads both times = ½ x ½ = ¼ B. Addition Rule1. Probability that one of two or more mutually exclusive outsomces will occur: add the probabilities of the possible outcomes a. Ex. Tossing a coin: probability it will land on heads or tails = ½ + ½ = 1 (100% chance)II. Inheritance of 2 Traits A. 2 factor cross (ex. seed color and shape)B. Possibilities1. 2 genes are physically linked, and are always inherited as a unita. Offspring will have same trait combinations as their parents2. 2 genes are not linked, and are inherited independently of eachothera. Some offspring will show new trait combinationsC. Example: Yellow/Round peas x Green/wrinkled1. Trait 1 = color; trait 2 = wrinkled vs. rounda. A = yellow; a = greenb. B = round; b = wrinkled2. Resulting plants show near perfect results expected based onpunnett square, proving genes for color and skin type are notlinked:D. Leads to Mendel’s Law of Independent Assortment1. Genes on different chromosomes are inherited independently (non-linked)2. Fig. 16.15 E. Phenotypic Ratios can be modified by interactions between genes (Fig. 16.16)(next page)III. Pedigree Analysis A. Fig.


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UD BISC 207 - Chapter 16 – Mendelian Genetics

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