BSC 219

9/4/12

Modifications of Mendelian genetics

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.

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

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

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

ABO blood group

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

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

Dominant epistasis

Duplicate recessive epistasis

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

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

Cytoplasmic inheritance

Genetic maternal effect

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

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.

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