Chapter 5 Outline

• 5.1 Dominance Is Interaction between Genes at the Same Locus, 100

• 5.2 Penetrance and Expressivity Describe How Genes Are Expressed as Phenotype, 102

• 5.3 Lethal Alleles May Alter Phenotypic Ratios, 103

• 5.4 Multiple Alleles at a Locus Create a Greater Variety of Genotypes and Phenotypes than Do Two Alleles, 103

Chapter 5 Outline

• 5.5 Gene Interaction Occurs When Genes at Multiple Loci Determine a Single Phenotype, 105

• 5.6 Sex Influences the Inheritance and Expression of Genes in a Variety of Ways, 114

• 5.7 Anticipation Is the Stronger or Earlier Expression of Traits in Succeeding Generations, 122

• 5.8 The Expression of a Genotype May Be Influenced by Environmental Effects, 122

5.1 Dominance Is Interaction between Genes at the Same Locus

• Genes at the same locus – two versions of the same gene; each version of the same gene is defined as allele.

5.1 Dominance Is Interaction between Genes at the Same Locus

• Incomplete dominance

• Codominance

• Penetrance: percentage of individuals having a particular genotype that express the expected phenotype

• Expressivity: the degree to which a character is expressed

5.2 Penetrance and Expressivity Describe How Genes Are Expressed as Phenotype

5.3 Lethal Alleles May Alter Phenotypic Ratios

• A lethal allele: causes death at an early stage of development, and so some genotypes may not appear among the progeny

More than 2 alleles at a locus

•Relationship between allele pairs determines outcome

•Could be exhibited as dominant/recessive relationship as in duck feathers

•Could be exhibited in codominance as in ABO blood type

5.4 Multiple Alleles at a Locus Create a Greater Variety of Genotypes and Phenotypes than Do Two Alleles

• ABO blood group

5.5 Gene Interaction Occurs When Genes at Multiple Loci Determine a Single Phenotype

• Gene interaction: Effects of genes at one locus depend on the presence of genes at other loci.

• Gene interaction that produces novel phenotypes

5.5 Gene Interaction Occurs When Genes at Multiple Loci Determine a Single Phenotype

• Gene interaction with epistasis

• Epistasis: One gene masks the effect of another gene.

• Recessive epistasis

5.5 Gene Interaction Occurs When Genes at Multiple Loci Determine a Single Phenotype

• Dominant epistasis

5.5 Gene Interaction Occurs When Genes at Multiple Loci Determine a Single Phenotype

• Duplicate recessive epistasis

5.5 Gene Interaction Occurs When Genes at Multiple Loci Determine a Single Phenotype

• Complementation: determines whether mutations are at the same locus or at different loci

• The complex genetics of coat color in dogs:• Agouti (A) locus• Black (B) locus• Extension (E) locus• Spotting (S) locus

5.6 Sex Influences the Inheritance and Expression of Genes in a Variety of Ways

• Sex-influenced and sex-limited characteristics

Sex-influenced and sex-limited characteristics

• Sex-influenced characteristics

Sex-influenced and sex-limited characteristics

• Sex-limited characteristics

Sex-influenced and sex-limited characteristics

• Cytoplasmic inheritance

Sex-influenced and sex-limited characteristics

• Genetic maternal effect

Sex-influenced and sex-limited characteristics

• Genomic imprinting: differential expression of genetic material depending on whether it is inherited from the male or female parent

• Epigenetics: phenomena due to alterations to DNA that do not include changes in the base sequence; often affects the way in which the DNA sequences are expressed

5.7 Anticipation Is the Stronger or Earlier Expression of Traits in Succeeding Generations

• Anticipation: A genetic trait becomes more strongly expressed or is expressed at an earlier stage as it is passed from generation to generation.

5.8 The Expression of a Genotype May Be Influenced by Environmental Effects

• Temperature-sensitive allele: an allele whose product is functional only at a certain temperature