Unformatted text preview: 204-325 1 Summary of the Last Lecture The chromosome theory of inheritance states that genes are located on chromosomes. Chromosome behavior during meiosis is the basis for Mendel's laws. Sex chromosomes are chromosomes that are represented differently in the two sexes. Sex linkage is the physical association of genes with the sex chromosomes. Such genes are called sex-linked genes. Organisms use several different mechanisms for sex determination.
2 Today's Topics 1. Multiple Alleles of One Gene 2. Incomplete Dominance and Codominance between Alleles 3. Gene Interactions: Phenotypes Controlled by More than One Gene 4. Gene and Environment 3 Topic 1 Multiple Alleles of One Gene
4 Allelic Series: More Than Two Alleles of a Gene 5 Mutations from Different Genes Complement Each Other
Complementation : Mutation 1 + Mutation 2 => Wild Type . 6 Mutations from Different Genes Complement Each Other
No Complementation : Mutation 1 + Mutation 2 => Mutant Phenotype
Mutations in the same gene: no complementation . 7 Complementation Defines Units of Function (Gene) . 8 Animation 1: Complementation 9 Allelic Series: More Than Two Alleles of a Gene 10 ABO Blood Type: 1 Gene, 3 Alleles, 4 Phenotypes 11 ABO Blood Type Gene Encodes a Glycosyltransferase Glycolipid 12 Human ABO Blood Type Antigens 13 Gene and Blood Type
O (Anti-B) (Anti-A) (None) (Anti-A, B) Antigens 14 Human ABO Blood Types
Recipient Blood Type Donor Blood Type X X X X X X X None 15 Blood Transfusion Rules Blood Transfusion
Blood Type Receive Blood? Give Blood? O AB A B O only Any type A, B, O O Any type AB only A, B, AB AB 16 Three Alleles: we Dominant Over w, but Recessive to w+ 17 Many Alleles of One Gene 18 A Lethal Allele Defines an Essential Gene X 19 Topic 2 Incomplete Dominance and Codominance between Alleles
20 Complete Dominant/Recessive 21 Incomplete Dominance in a Monohybrid 22 Incomplete Dominance: Intermediate Phenotype in Heterozygote 23 Incomplete Dominance in Horse Coat Color 24 Another Example of Incomplete Dominance 25 Codominance: Heterozygote has both Phenotypes 26 Animation 2: Incomplete Dominance and Codominance 27 Types of Dominance 28 Topic 3 Gene Interactions: Phenotypes Controlled by More than One Gene
29 Interaction of Several Genes Determines a Phenotype 30 Two Genes for One Trait and Non-episatic Interaction new phenotype new phenotype new phenotype 31 Duplicate None-epistatic Interaction in a Dihybrid (9:6:1) 32 Epistasis: Genotype of One Gene Masks Effects of Another Gene white c/c is always albino no matter what B alleles are c/c masks the effect of B alleles c/c is epistatic to gene B
Recessive Epistasis 33 9:3:4 Recessive Epistasis Dihybrid: 9:3:4 Ratio in F2 C is epistatic to A 34 Epistasis in a Linear Biochemical Pathway
c/c masks gene A Gene C is epistatic to Gene A Gene C Gene A Agouti Black A genotype of one gene (called epistatic gene) renders the genotype of a second gene (called hypostatic gene) irrelevant: the phenotype will be dictated by the genotype of the epistatic gene alone.
35 White Dominant Epistasis Dihybrid: 12:3:1 Ratio in F2 W/- is white no matter what Y alleles are. 36 Model for the Dominant Epistasis Dihybrid 12:3:1 Ratio 37 Duplicate Recessive Epistasis Dihybrid: 9:7 Ratio in F2 White 1 Gene C White 2 Gene P Purple c/c is white no matter what P alleles are ; p/p is white no matter what C alleles are
38 Many Possible Modifications of a Dihybrid Outcome 39 Sex-influenced Inheritance of Pattern Baldness Distinguish: Sex-Linked Sex-Limited Sex-Influenced 40 Sex-influenced Inheritance of Pattern Baldness b is an autosomal gene b is dominant in but recessive in Sex Influnced 41 Topic 4 Gene and Environment
42 Influences on the Phenotype . 43 Genotype to Phenotype Penetrance: Percentage of the individuals of a genotype has any phenotypes Example: ABO blood type is 100% penetrant. Expressivity: Degree to which a penetrant gene is phenotypically expressed in an individual. 44 Phenotypes from Same Allele 45 Penetrance and Expressivity of a Genotype 46 Temperature Affects Phenotypes 47 Environmental Variables Can Affect Gene Action Same Genotype, Different Soil Acidity
48 Summary More than 2 alleles of a gene could exist in a population. However, an individual possesses only 2 alleles of a gene. Complementation test determines if 2 mutants are allelic. The relationship between two alleles of a gene in an individual could be complete dominance, incomplete dominance or codominance. More than one genes often interact to determine a phenotype. Gene interaction and epistasis could modify Mendelian ratios. Penetrance and expressivity describe the phenotype frequency in a population and degree in an individual respectively. The genetic makeup specifies the potential to develop and function. Internal and external environment affects the realization of the potential.
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- Spring '08