Chapter 16 Mendelian Genetics Part A I Introduction to Mendel s Experiments A Studied trait inheritance B Blended Inheritance was the popular idea at the time 1 Offspring were averages of their parents a Tall father short mother medium children b Their children would pass on the trait of medium height to their offspring C Mendel s Model System peas 1 Normally self fertilize 2 Used true breeding plants that when self fertilized produced offspring with consistent traits 3 Focused on 7 traits 2 variants of each one 4 Cross fertilized his variants D Single Factor Cross focuses on 1 trait 1 P parental 2 F1 first filial generation offspring of P cross a Offspring are monohybrids 3 F2 generation offspring of F1 cross E Plant height experiment 1 P generation true breeding tall x short a True breeding TT x tt b Based on theories at the time experiment should yield medium plants but produces all tall c F1 is not true breeding 2 P TT tt plants 3 F1 Tt plants produced from P cross T Tt Tt T Tt Tt t t t T T TT Tt tt t Tt P cross true breeding TT x tt F1 cross Tt x Tt 4 Tt heterozygous TT homozygous dominant tt homozygous recessive 5 Data supports particulate inheritance a Offspring inherit traits as unchanging discrete hereditary units genes II Genes come in different forms Alleles A Dominant recessive 1 Incomplete dominance cases where 2 alleles if both present both contribute to phenotype B Location of Gene on chromosomes is its locus C Principle of Segregation alleles are separated during gamete formation fig 16 9 1 III Test Cross A Cross to determine genotype of an B Crosses unknown genotype with a unknown homozygous recessive aa individual to reveal the unknown genotype based on resulting plants 1 Ex Cross an unknown tall plant Could be TT or Tt with a tt a b If some of the F1 plants are short unknown parent is Tt If all F1 plants are tall unknown parent is TT Part B I Predicting Trait Inheritance Patterns Probability Rules A Product Rule 1 If 2 or more independent events need to occur probability of both happening is the product of each one s individual probability 2 Ex Tossing a coin probability it will land on heads both times x B Addition Rule 1 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 1 100 chance II Inheritance of 2 Traits A 2 factor cross ex seed color and shape B Possibilities 1 2 genes are physically linked and are always inherited as a unit a Offspring will have same trait combinations as their parents 2 2 genes are not linked and are inherited independently of each other a Some offspring will show new trait combinations C Example Yellow Round peas x Green wrinkled 1 Trait 1 color trait 2 wrinkled vs round a A yellow a green b B round b wrinkled 2 Resulting plants show near perfect results expected based on punnett square proving genes for color and skin type are not linked D Leads to Mendel s Law of Independent Assortment 1 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 16 15 III Pedigree Analysis A Fig 16 17 16 15
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