Genetics 7th Edition Lecture Slides - Chapter 5 PDF

Benjamin A. Pierce Genetic s A Conceptual Approach SEVENTH EDITION Lecture Slides CHAPTER 5 Extensions and Modifications of Basic Principles Copyright © 2020, W.H. Freeman and Company Extens...

Benjamin A. Pierce Genetic s A Conceptual Approach SEVENTH EDITION Lecture Slides CHAPTER 5 Extensions and Modifications of Basic Principles Copyright © 2020, W.H. Freeman and Company Extensions and Modifications of Basic Principles 5.1 Additional Factors at a Single Locus Can Affect the Results of Genetic Crosses (1 of 11) Genes at the same locus—two versions of the same gene; each version of the same gene is defined as allele Types of dominance – Complete dominance – Incomplete dominance – Codominance 5.1 Additional Factors at a Single Locus Can Affect the Results of Genetic Crosses (2 of 11) 5.1 Additional Factors at a Single Locus Can Affect the Results of Genetic Crosses (3 of 11)  Concept Check 1 (1 of 2) If an F1 eggplant in Figure 5.2 is used in a testcross, what proportion of the progeny from this cross will be white? a. all the progeny b. 1/2 c. 1/4 d. 0  Concept Check 1 (2 of 2) If an F1 eggplant in Figure 5.2 is used in a testcross, what proportion of the progeny from this cross will be white? a. all the progeny b. 1/2 c. 1/4 d. 0 TABLE 5.1 Differences between complete dominance, incomplete dominance, and codominance Type of Dominance Definition Complete dominance Phenotype of the heterozygote is the same as the phenotype of one of the homozygotes. Incomplete Phenotype of the heterozygote is intermediate dominance (falls within the range) between the phenotypes of the two homozygotes. Codominance Phenotype of the heterozygote includes the phenotypes of both homozygotes.  5.1 Additional Factors at a Single Locus Can Affect the Results of Genetic Crosses (4 of 11) Level of phenotype may affect dominance. Example: CFTR – Channel in the membrane that regulates chloride levels – Mutated in cystic fibrosis – In CF, mutated channel stays closed, so chloride ions build up in cell – In heterozygotes, enough functional CFTR is made to prevent cystic fibrosis  Concept Check 2 (1 of 2) How do complete dominance, incomplete dominance, and codominance differ?  Concept Check 2 (2 of 2) How do complete dominance, incomplete dominance, and codominance differ? Complete dominance: The heterozygote expresses the same phenotype as one of the homozygotes. Incomplete dominance: The heterozygote has a phenotype that is intermediate between those of the two homozygotes. Codominance: The heterozygote has a phenotype that simultaneously expresses the phenotypes of both homozygotes.  5.1 Additional Factors at a Single Locus Can Affect the Results of Genetic Crosses (5 of 11) Penetrance: the percentage of individuals having a particular genotype that express the expected phenotype Expressivity: the degree to which a trait is expressed 5.1 Additional Factors at a Single Locus Can Affect the Results of Genetic Crosses (6 of 11)  Concept Check 3 (1 of 2) How does incomplete dominance differ from incomplete penetrance? a. Incomplete dominance refers to alleles at the same locus; incomplete penetrance refers to alleles at different loci. b. Incomplete dominance ranges from 0% to 50%; incomplete penetrance ranges from 51% to 99%. c. In incomplete dominance, the heterozygote is intermediate between the homozygotes; in incomplete penetrance, heterozygotes express phenotypes of both homozygotes. d. In incomplete dominance, the heterozygote is intermediate between the homozygotes; in incomplete penetrance, some individuals do not express the expected phenotype.  Concept Check 3 (2 of 2) How does incomplete dominance differ from incomplete penetrance? a. Incomplete dominance refers to alleles at the same locus; incomplete penetrance refers to alleles at different loci. b. Incomplete dominance ranges from 0% to 50%; incomplete penetrance ranges from 51% to 99%. c. In incomplete dominance, the heterozygote is intermediate between the homozygotes; in incomplete penetrance, heterozygotes express phenotypes of both homozygotes. d. In incomplete dominance, the heterozygote is intermediate between the homozygotes; in incomplete penetrance, some individuals do not express the expected phenotype.  5.1 Additional Factors at a Single Locus Can Affect the Results of Genetic Crosses (7 of 11) A lethal allele causes death at an early stage of development, so some genotypes may not appear among the progeny. Affects the Mendelian genotypic and phenotypic ratios in progeny. 5.1 Additional Factors at a Single Locus Can Affect the Results of Genetic Crosses (8 of 11)  Concept Check 4 (1 of 2) A cross between two green corn plants yields 2/3 progeny that are green and 1/3 progeny that are yellow. What is the genotype of the green progeny? a. WW b. Ww c. ww d. W_(WW and Ww)  Concept Check 4 (2 of 2) A cross between two green corn plants yields 2/3 progeny that are green and 1/3 progeny that are yellow. What is the genotype of the green progeny? a. WW b. Ww c. ww d. W_(WW and Ww)  5.1 Additional Factors at a Single Locus Can Affect the Results of Genetic Crosses (9 of 11) Multiple alleles: For a given locus, more than two alleles are present within a group of individuals. ABO blood group. 5.1 Additional Factors at a Single Locus Can Affect the Results of Genetic Crosses (10 of 11) 5.1 Additional Factors at a Single Locus Can Affect the Results of Genetic Crosses (11 of 11)  Concept Check 5 (1 of 2) How many genotypes are possible at a locus with five alleles? a. 30 b. 27 c. 15 d. 5  Concept Check 5 (2 of 2) How many genotypes are possible at a locus with five alleles? a. 30 b. 27 c. 15 d. 5  5.2 Gene Interaction Takes Place when Genes at Multiple Loci Determine a Single Phenotype (1 of 8) Gene interaction: Effects of genes at one locus depend on the presence of genes at other loci. Genes exhibit independent assortment but do not act independently in their phenotypic expression. The products of genes at different loci that interact to produce new phenotypes.  Concept Check 6 (1 of 2) How does gene interaction differ from dominance?  Concept Check 6 (2 of 2) How does gene interaction differ from dominance? Gene interaction is interaction between genes at different loci. Dominance is interaction between alleles at a single locus.  Gene Interaction That Produces Novel Phenotypes (1 of 2) Gene interaction: The effect of a gene at one locus depends on the presence of a gene at other loci. −9:3:3:1 F2 ratio of phenotype but only ONE trait (9:3:3:1 F2 ratio in dihybrid is TWO traits) Gene Interaction That Produces Novel Phenotypes (2 of 2)  5.2 Gene Interaction Takes Place when Genes at Multiple Loci Determine a Single Phenotype (2 of 8) Epistasis: One gene masks the effect of another gene. – Recessive epistasis 9:3:4 F2 ratio (Fig. 5.8) – Dominant epistasis 12:3:1 F2 ratio (Fig. 5.9) – Duplicate recessive epistasis 9:7 F2 ratio (Fig. 5.10)  5.2 Gene Interaction Takes Place when Genes at Multiple Loci Determine a Single Phenotype (3 of 8)  5.2 Gene Interaction Takes Place when Genes at Multiple Loci Determine a Single Phenotype (4 of 8)  5.2 Gene Interaction Takes Place when Genes at Multiple Loci Determine a Single Phenotype (5 of 8)  TABLE 5.2 Modified dihybrid phenotypic ratios due to gene interaction Ratio* Genotype: Genotype: Genotype: Genotype: Type of Example Discussed in Chapter A_ B_ A_ bb aa B_ aa bb Interaction 9:3:3:1 9 3 3 1 None Seed shape and seed color in peas 9:3:4 9 3 4 4 Recessive Coat color in Labrador retrievers epistasis 12 : 3 : 1 12 12 3 1 Dominant Color in squash epistasis 9:7 9 7 7 7 Duplicate Albinism in snails recessive epistasis 9:6:1 9 6 6 1 Duplicate ─ interaction 15 : 1 15 15 15 1 Duplicate ─ dominant epistasis 13 : 3 13 13 3 Dominant and ─ recessive epistasis *Each ratio is produced by a dihybrid cross (Aa Bb × Aa Bb). Shaded bars represent combinations of genotypes that give the same phenotype.  Concept Check 7 (1 of 2) A number of all-white cats are crossed, and they produce the following types of progeny: 12/16 all- white, 3/16 black, and 1/16 gray. What is the genotype of the black progeny? a. Aa b. Aa Bb c. A_ B_ d. A_ bb  Concept Check 7 (2 of 2) A number of all-white cats are crossed, and they produce the following types of progeny: 12/16 all- white, 3/16 black, and 1/16 gray. What is the genotype of the black progeny? a. Aa b. Aa Bb c. A_ B_ d. A_ bb  5.2 Gene Interaction Takes Place when Genes at Multiple Loci Determine a Single Phenotype (6 of 8) Complementation: Determine whether mutations are at the same locus or at different loci. Test: Parents homozygous for different mutations are crossed; offspring are heterozygous. If mutations are allelic (occur at the same locus) – Heterozygous offspring have only mutant alleles. – Exhibit a mutant phenotype. If mutations occur at different loci – Heterozygous offspring inherit a mutant allele and a wild- type allele. – I Exhibit wild-type phenotype.  Concept Check 8 (1 of 2) Brindle (tiger-striped appearance) is a recessive trait in bulldogs and in Chihuahuas. What types of crosses would you carry out to determine whether the brindle genes in bulldogs and in Chihuahuas are at the same locus?  Concept Check 8 (2 of 2) Brindle (tiger-striped appearance) is a recessive trait in bulldogs and in Chihuahuas. What types of crosses would you carry out to determine whether the brindle genes in bulldogs and in Chihuahuas are at the same locus? Cross a bulldog homozygous for brindle with a Chihuahua homozygous for brindle. If the two brindle genes are allelic, all the offspring will be brindle: bb x bb = all bb (brindle). If brindle in the two breeds is due to recessive genes at different loci, then none of the offspring will be brindle: a+a+ bb x aa b+b+ = a+a b+b  5.2 Gene Interaction Takes Place when Genes at Multiple Loci Determine a Single Phenotype (7 of 8) The complex genetics of coat color in dogs: – Agouti (A) locus – Black (B) locus – Extension (E) locus – Spotting (S) locus  5.2 Gene Interaction Takes Place when Genes at Multiple Loci Determine a Single Phenotype (8 of 8)  TABLE 5.3 Common genotypes in different breeds of dogs Breed Usual Homozygous Genotypes* Other Alleles Present Within the Breed Basset hound BB EE ay,at S, sP, si Beagle asas BB sPsP E, e English bulldog BB As, ay, at Em, E, ebr S, si, sP, sw Chihuahua As, ay, as, at B, b Em, E, ebr, e S, si, sP, sw Collie BB EE ay, a t s i, s w Dalmatian AsAs Eewsw B, b Doberman atat EE SS B, b German shepherd BB SS ay, a, as, at Em, E, e Golden retriever AsAs BB SS E, e Greyhound BB As, ay E, ebr, e S, sP, sw, si Irish setter BB ee SS As, at Labrador retriever AsAs SS B, b E, e Poodle SS As, at B, b E, e Rottweiler atat BB EE SS St. Bernard ayay BB Em, E si, sp, sw *Most dogs in the breed are homozygous for these genes; a few individual dogs may possess other alleles at these loci. Source: Data from M. B. Willis, Genetics of the Dog (London: Witherby, 1989). 5.3 Sex Influences the Inheritance and Expression of Genes in a Variety of Ways (1 of 10) Sex-influenced and sex-limited characteristics – Sex-influenced characteristics (Fig. 5.12) – Sex-limited characteristics (Fig. 5.13) – Cytoplasmic inheritance (Figs. 5.15 and 5.16) 5.3 Sex Influences the Inheritance and Expression of Genes in a Variety of Ways (2 of 10) 5.3 Sex Influences the Inheritance and Expression of Genes in a Variety of Ways (3 of 10) 5.3 Sex Influences the Inheritance and Expression of Genes in a Variety of Ways (4 of 10)  Concept Check 9 (1 of 2) How do sex-influenced and sex-limited characteristics differ from sex-linked characteristics?  Concept Check 9 (2 of 2) How do sex-influenced and sex-limited characteristics differ from sex-linked characteristics? Both sex-influenced and sex-limited characteristics are encoded by autosomal genes whose expression is affected by the sex of the individual organism possessing the genes. Sex-linked characteristics are encoded by genes on the sex chromosomes. 5.3 Sex Influences the Inheritance and Expression of Genes in a Variety of Ways (5 of 10)  TABLE 5.4 Characteristics of cytoplasmically inherited traits 1. Present in males and females. 2. Usually inherited from one parent, typically the maternal parent. 3. Reciprocal crosses give different results. 4. Exhibit extensive phenotypic variation, even within a single family. 5.3 Sex Influences the Inheritance and Expression of Genes in a Variety of Ways (6 of 10) 5.3 Sex Influences the Inheritance and Expression of Genes in a Variety of Ways (7 of 10) Sex-influenced and sex-limited characteristics – Genetic maternal effect (Fig. 5.17) 5.3 Sex Influences the Inheritance and Expression of Genes in a Variety of Ways (8 of 10)  Concept Check 10 (1 of 2) How might you determine whether a particular trait is due to cytoplasmic inheritance or to genetic maternal effect?  Concept Check 10 (2 of 2) How might you determine whether a particular trait is due to cytoplasmic inheritance or to genetic maternal effect? Cytoplasmically inherited traits are encoded by genes in the cytoplasm (usually inherited only from the female parent). A trait due to cytoplasmic inheritance will always be passed through females. Traits due to genetic maternal effect are encoded by autosomal genes and can therefore be passed through males, although any individual organism’s trait is determined by the genotype of the maternal parent. 5.3 Sex Influences the Inheritance and Expression of Genes in a Variety of Ways (9 of 10) Sex-influenced and sex-limited characteristics – Epigenetics: phenomena due to alterations to DNA that do not include changes in the base sequence; often affect the way in which the DNA sequences are expressed – Genomic imprinting is a type of epigentics: differential expression of genetic material depending on whether it is inherited from the male or female parent (Fig. 5.18) 5.3 Sex Influences the Inheritance and Expression of Genes in a Variety of Ways (10 of 10)  TABLE 5.5 Influences of sex on heredity Genetic Phenomenon Phenotype Determined by Sex-linked characteristic Genes located on the sex chromosomes Sex-influenced characteristic Autosomal genes that are more readily expressed in one sex Sex-limited characteristic Autosomal genes whose expression is limited to one sex Genetic maternal effect Nuclear genotype of the maternal parent Cytoplasmic inheritance Cytoplasmic genes, which are usually inherited from only one parent Genomic imprinting Genes whose expression is affected by the sex of the transmitting parent  Concept Check 11 (1 of 2) What type of epigenetic mark is responsible for genomic imprinting?  Concept Check 11 (2 of 2) What type of epigenetic mark is responsible for genomic imprinting? Methylation of DNA  5.4 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. Anticipation occurs due to expansion of an unstable region of DNA from generation to generation.  5.5 The Expression of a Genotype May Be Influenced by Environmental Effects (1 of 2) A temperature-sensitive allele is an allele whose product is functional only at certain temperature.  5.5 The Expression of a Genotype May Be Influenced by Environmental Effects (2 of 2)  Concept Check 12 (1 of 2) How can you determine whether a phenotype such as reduced eyes in fruit flies is due to a recessive mutation or is a phenocopy?  Concept Check 12 (2 of 2) How can you determine whether a phenotype such as reduced eyes in fruit flies is due to a recessive mutation or is a phenocopy? Cross two eyeless flies and cross an eyeless fly with a wild-type fly. – Raise the offspring of both crosses in the same environment. If the trait is due to a recessive mutation: – All the offspring of the two eyeless flies should be eyeless. – Some of the offspring of the eyeless and wild- type flies should be wild type. If the trait is a phenocopy: – No differences in the progeny of the two crosses  The Inheritance of Continuous Characteristics Discontinuous characteristics: relatively few phenotypes Continuous characteristics: continuous distribution of phenotypes; occurs when genes at many loci interact Polygenic characteristics: characteristics encoded by genes at many loci Pleiotropy: one gene affects multiple characteristics  Concept Check 13 (1 of 2) What is the difference between polygeny and pleiotropy?  Concept Check 13 (2 of 2) What is the difference between polygeny and pleiotropy? Polygeny refers to the influence of multiple genes on the expression of a single characteristic. Pleiotropy refers to the effect of a single gene on the expression of multiple characteristics.