Transcript 9/04 Modifications of Mendel

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
5.2 Penetrance and Expressivity Describe
How Genes Are Expressed as Phenotype
• Penetrance: percentage of individuals having a
particular genotype that express the expected
phenotype
• Expressivity: the degree to which a character is
expressed
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