Genetics: A Conceptual Approach © 2009 W. H. Freeman and Company Benjamin A. Pierce Genetics: A Conceptual Approach THIRD EDITION CHAPTER 5 Extensions and Modifications of Basic Principles © 2009 W. H. Freeman and Company Copyright 2008 © W. H. Freeman and Company

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.]

5.1 The 2:1 ratio produced by a cross between two yellow mice results from a lethal allele.

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.

5.2 The type of dominance exhibited by a trait depends on how the phenotype of the heterozygote relates to the phenotypes of the homozygotes.

5.3 Human polydactyly (extra digits) exhibits incomplete penetrance and variable expressivity. [SPL/Photo Researchers.]

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).

5.5 ABO blood types and possible blood transfusions.

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.

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

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

5.7 A multistep biochemical pathway synthesizes the carotenoid pigments responsible for color variation in peppers.

5.7 A multistep biochemical pathway synthesizes the carotenoid pigments responsible for color variation in peppers.

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.

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.

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

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.

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

5.11a Coat color in dogs is determined by interactions between genes at a number of loci. (a) Most Labrador retrievers are genotype AsAs SS, varying only at the B and E loci. [Part a: Kent and Donna Dannen.]

5.11b Coat color in dogs is determined by interactions between genes at a number of loci. (b) Most beagles are genotype asas BB spsp. [Part b: Tara Darling.]

5.11c Coat color in dogs is determined by interactions between genes at a number of loci. (c) Dalmations are genotype AsAs EE swsw, varying at the B locus, which makes the dogs black (B_) or brown (bb). [Part c: PhotoDisc.]

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

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

5.12b Genes that encode sex-influenced traits are inherited according to Mendel’s 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.]

5.14 Sex-limited characteristics are inherited according to Mendel’s principles. Precocious puberty is an autosomal dominant trait that is limited to males.

5.14 Sex-limited characteristics are inherited according to Mendel’s principles. Precocious puberty is an autosomal dominant trait that is limited to males.

5.14a Sex-limited characteristics are inherited according to Mendel’s principles. Precocious puberty is an autosomal dominant trait that is limited to males.

5.14a Sex-limited characteristics are inherited according to Mendel’s principles. Precocious puberty is an autosomal dominant trait that is limited to males.

5.14b Sex-limited characteristics are inherited according to Mendel’s principles. Precocious puberty is an autosomal dominant trait that is limited to males.

5.14b Sex-limited characteristics are inherited according to Mendel’s principles. Precocious puberty is an autosomal dominant trait that is limited to males.

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.

5.15 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-oﾕclocks 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 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.

5.18a Genomic imprinting of the lgf2 gene in mice and humans affects fetal growth. (a) The paternal lgf2 allele is active in the fetus and placenta, whereas the maternal allele is silent. [Courtesy of Dr. Thomas Ried and Dr. Evelin Schrock.]

5.18a Genomic imprinting of the lgf2 gene in mice and humans affects fetal growth. (a) The paternal lgf2 allele is active in the fetus and placenta, whereas the maternal allele is silent. [Courtesy of Dr. Thomas Ried and Dr. Evelin Schrock.]

5.18b Genomic imprinting of the lgf2 gene in mice and humans affects fetal growth. (b) The human lgf2 locus is on the short arm of chromosome 11; the locus in mice is on chromosome 7. [Courtesy of Dr. Thomas Ried and Dr. Evelin Schrock.]

5.19 Norm of reaction is the range of phenotypes produced by a genotype in different environments. This norm of reaction is for individual Drosophila flies homozygous for vestigial wings. [Data from M. H. Harnly, Journal of Experimental Zoology 56:363ﾐ379, 1936.]

5.20 The expression of some genotypes depends on specific environments. The expression of a temperature-sensitive allele, himalayan, is shown in rabbits reared at different temperatures.