Chapter 5 Outline5.1 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 Outline5.5 Gene Interaction Occurs When Genes at Multiple Loci Determine a Single Phenotype, 1055.6 Sex Influences the Inheritance and Expression of Genes in a Variety of Ways, 1145.7Anticipation 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 LocusGenes 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 LocusIncomplete dominance

Codominance

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

Expressivity: the degree to which a character is expressed5.2 Penetrance and Expressivity Describe How Genes Are Expressed as Phenotype

5.3 Lethal Alleles May Alter Phenotypic RatiosA 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 locusRelationship 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 AllelesABO blood group

5.5 Gene Interaction Occurs When Genes at Multiple Loci Determine a Single PhenotypeGene 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 PhenotypeGene 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 PhenotypeDominant epistasis

5.5 Gene Interaction Occurs When Genes at Multiple Loci Determine a Single PhenotypeDuplicate recessive epistasis

5.5 Gene Interaction Occurs When Genes at Multiple Loci Determine a Single PhenotypeComplementation: determines whether mutations are at the same locus or at different loci

The complex genetics of coat color in dogs:Agouti (A) locusBlack (B) locusExtension (E) locusSpotting (S) locus

5.6 Sex Influences the Inheritance and Expression of Genes in a Variety of WaysSex-influenced and sex-limited characteristics

Sex-influenced and sex-limited characteristicsSex-influenced characteristics

Sex-influenced and sex-limited characteristicsSex-limited characteristics

Sex-influenced and sex-limited characteristicsCytoplasmic inheritance

Sex-influenced and sex-limited characteristicsGenetic maternal effect

Sex-influenced and sex-limited characteristicsGenomic 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 GenerationsAnticipation: 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 EffectsTemperature-sensitive allele: an allele whose product is functional only at a certain temperature

****5.2 The type of dominance exhibited by a trait depends on how the phenotype of the heterozygote relates to the phenotypes of the homozygotes.*****Yellow coat color in mice is caused by a recessive lethal gene, producing distorted phenotypic ratios in the progeny of two yellow mice.William Castle and Clarence Little discovered the lethal nature of the yellow gene in 1910. [Reprinted with permission of Dr. Loan Phan and In Vivo, a publication of Columbia University Medical Center.]*5.4 Mendels principle of segregation applies to crosses with multiple alleles. In this example, three alleles determine the type of plumage in mallard ducks: MR (restricted) M (mallard) md (dusky).**5.5 ABO blood types and possible blood transfusions.**5.6 Gene interaction in which two loci determine a single characteristic, fruit color, in the pepper Capsicum annuum.**5.8 Expression of the ABO antigens depend on alleles at the H locus. The H locus encodes a precursor to the antigens called compound H. Alleles at the ABO locus determine which types of terminal sugars are added to compound H.**5.9 Yellow pigment in summer squash is produced in a two-step pathway.**5.10 Pigment is produced in a two-step pathway in snails.*****5.12 Genes that encode sex-influenced traits are inherited according to Mendels principles but are expressed differently in males and females.*5.12a Genes that encode sex-influenced traits are inherited according to Mendels principles but are expressed differently in males and females.*5.12b Genes that encode sex-influenced traits are inherited according to Mendels principles but are expressed differently in males and females.**5.13a A sex-limited characteristic is encoded by autosomal genes that are expressed in only one sex. An example is cock feathering in chickens, an autosomal recessive trait that is limited to males. (a) Cock-feathered male. [Larry Lefever/Grant Heilman Photography.]*5.13b A sex-limited characteristic is encoded by autosomal genes that are expressed in only one sex. An example is cock feathering in chickens, an autosomal recessive trait that is limited to males. (b) Hen-feathered female. [Larry Lefever/Grant Heilman Photography.]*5.13c A sex-limited characteristic is encoded by autosomal genes that are expressed in only one sex. An example is cock feathering in chickens, an autosomal recessive trait that is limited to males. (c) Hen-feathered male. [Larry Lefever/Grant Heilman Photography.]**5.15 Cytoplasmically inherited characteristics frequently exhibit extensive phenotypic variation because cells and individual offspring contain various proportions of cytoplasmic genes. Mitochondria that have wild-type mtDNA are shown in red; those having mutant mtDNA are shown in blue.*5.16 Crosses for leaf type in four-oclocks illustrate cytoplasmic inheritance.**5.17 In genetic maternal effect, the genotype of the maternal parent determines the phenotype of the offspring. The shell coiling of a snail is a trait that exhibits genetic maternal effect.*5.17 (part 1) In genetic maternal effect, the genotype of the maternal parent determines the phenotype of the offspring. The shell coiling of a snail is a trait that exhibits genetic maternal effect.*5.17 (part 1) In genetic maternal effect, the genotype of the maternal parent determines the phenotype of the offspring. The shell coiling of a snail is a trait that exhibits genetic maternal effect.*5.17 (part 2) In genetic maternal effect, the genotype of the maternal parent determines the phenotype of the offspring. The shell coiling of a snail is a trait that exhibits genetic maternal effect.***