1. 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

2. 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

3. 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.

4. 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.

5. 5.1 Dominance Is Interaction between Genes at the Same Locus
Incomplete dominance
Codominance

7. 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

8. 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

9. 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 [Reprinted with permission of Dr. Loan Phan and In Vivo, a publication of Columbia University Medical Center.]

11. 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

12. 5.4 Mendel’s 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).

13. 5.4 Multiple Alleles at a Locus Create a Greater Variety of Genotypes and Phenotypes than Do Two Alleles
ABO blood group

14. 5.5 ABO blood types and possible blood transfusions.

15. 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

16. 5.6 Gene interaction in which two loci determine a single characteristic, fruit color, in the pepper Capsicum annuum.

17. 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

18. 5. 8 Expression of the ABO antigens depend on alleles at the H locus
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.

19. 5.5 Gene Interaction Occurs When Genes at Multiple Loci Determine a Single Phenotype
Dominant epistasis

20. 5.9 Yellow pigment in summer squash is produced in a two-step pathway.

21. 5.5 Gene Interaction Occurs When Genes at Multiple Loci Determine a Single Phenotype
Duplicate recessive epistasis

22. 5.10 Pigment is produced in a two-step pathway in snails.

24. 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

27. 5.6 Sex Influences the Inheritance and Expression of Genes in a Variety of Ways
Sex-influenced and sex-limited characteristics

28. Sex-influenced and sex-limited characteristics
Sex-influenced characteristics

29. 5.12 Genes that encode sex-influenced traits are inherited according to Mendel’s principles but are expressed differently in males and females.

30. 5.12a Genes that encode sex-influenced traits are inherited according to Mendel’s principles but are expressed differently in males and females.

31. 5.12b Genes that encode sex-influenced traits are inherited according to Mendel’s principles but are expressed differently in males and females.

32. Sex-influenced and sex-limited characteristics

33. 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.]

34. 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.]

35. 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.]

36. Sex-influenced and sex-limited characteristics
Cytoplasmic inheritance

37. 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.

38. 5.16 Crosses for leaf type in four-oﾕclocks illustrate cytoplasmic inheritance.

39. Sex-influenced and sex-limited characteristics
Genetic maternal effect

40. 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.

41. 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.

42. 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.

43. 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.

44. 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

45. 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.

46. 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