Chapter 2

Module 3 (Chapter 2) Homework: 1. Two alleles of gene C control hair color in horses: C1 and C2. Horses homozygous for allele C1 are red, heterozygotes are yellow, and C2 homozygotes are cream. What type of allele interaction is described?  Incomplete dominance 2. If a trait is controlled by two different genes, a possible interaction between alleles of these genes can be called:  Epistasis 3. Curly-winged flies mate with pure-breeding straight-winged (wild-type) flies. The curly-winged F1 mate with each other to produce an F2 generation that consists of 160 flies with curly wings and 80 with straight wings. What can you infer from this observation?  The dominant curly wing allele is also a recessive lethal. ***lethal alleles are when there is a 2:1 ratio instead of a 3:1 ratio; 80 is half of 160 so this is a 2:1 ratio (this is recessive lethal because the progeny did not die that displayed the dominant curly-winged gene, but if dominant lethal, then the progeny with the dominant curly-winged gene would have died/eventually died). 4. What can explain the phenomenon where in different individuals, a particular genotype might give rise to different phenotypes?  Penetrance and expressivity ***The term penetrance is used to describe a proportion of individuals with a particular genotype who showed the expected phenotype; the term expressivity refers to the degree or intensity with which a particular genotype is expressed in a phenotype (shown in the genotype for cancer retinoblastoma). 5. Two alleles of gene C control hair color in horses: C1 and C2. Horses homozygous for allele C1 are red, heterozygotes are yellow, and C2 homozygotes are cream. In the offspring of mating’s’ between heterozygotes, what phenotypic ratio is expected?  1 red: 2 yellow: 1 cream

***Because this is mating between heterozygotes & we do not know if C1 or C2 are recessive or dominant traits, we know that the more common progeny will be the heterozygote phenotype (yellow) and the homozygous phenotypes will be expressed equally to each other (when crossing two heterozygotes – you will have four results showing the different phenotypic outcomes). 6. If a trait is controlled by two codominant alleles of one gene, what phenotypic ratio is expected in the offspring of a mating of two heterozygotes?  1:2:1 7. Which genotypic ratio indicates a recessive lethal allele when two heterozygotes are mated?  2:1 8. ABO blood types demonstrates which of the following inheritance patterns? (Check all that apply)  Pleiotropy  Codominance 9. A particular flower can be blue, red, or white. A pure-breeding red- flowered plant is crossed with a pure-breeding white-flowered one. The F1 are then crossed to produce an F2 generation. Which of the following phenotypic ratios in the F2 indicate that flower color in these two strains is controlled by two genes? RW Rw rW rw RW RRWW (R) RRWw (R) RrWW (R) RrWw (R) Rw RRWw (R) RRww (B) RrWw (R) Rrww (B) rW RrWW (R) RrWw (R) rrWW (W) rrWw (W) rw RrWw (R) Rrww (B) rr Ww (W) rrww (B) R = red W = white B = blue  9:3:4

 The population will have continuous variation in phenotypic expression. 16. A particular flower can be purple, blue, red, or white. A pure-breeding purple-flowered plant is crossed with a pure-breeding white flowered plant and the F1 are then crossed to produce an F2 generation. Which phenotypic ratio in the F2 may indicate that flower color in these plants is controlled by two genes that interact additively?  9:3:3:1 Required information for questions 17-19: In dogs, the dominant allele E (of gene E ) specifies dark pigment; the recessive e allele specifies a light pigment (cream). Genes A and K determine how the phenotype associated with the E allele is expressed. The dominance series for A gene alleles is A Y (fawn) > a w (gray) > a t (tan belly). The dominance series for the gene K alleles is K b (solid color) > k br (brindled) > k y (gene A markings expressed normally). Note that of all the gene K alleles, only the k y allele allows the phenotypes associated with the gene A genotypes to be expressed normally. Also the ee genotype is epistatic to all alleles of genes A and K. ***Epistatic genotype: is a circumstance where the expression of one gene is modified (such as being masked, inhibited, or suppressed) by the expression of one or more genes) 17. What is the coat color of a dog with the genotype Eek y k y A Y a w ?  Fawn ***The Ee genotype means that the darker pigment will be expressed and k y means that gene A markings will be expressed normally; since A Y (the fawn color) is dominant to a w (the gray color), the coat color of the dog will be expressed as the dominant phenotype (fawn). 18. Which of the following genotypes could a gray dog have?  E Ek y k y a w a t ***The EE genotype means that the darker pigment will be expressed and k y means that gene A markings will be expressed normally; since both a phenotypes

are recessive but the a w (the gray color) is dominant to a t (the tan belly color), the coat color of the dog will be expressed as the more dominant phenotype (gray). 19. Using the at-home genetic test ‘39Fetch’ you discover that your dog is ee. What color is your dog’s coat?  Cream ***only the recessive e genotype is present, so the only coat color option is cream ( A and K phenotypes are only dependent on the E genotype). 20. I n dogs, Gene B specifies a protein required for eumelanin (dark pigment) deposition. Protein B (specified by the B allele) deposits eumelanin densely so that the dog’s hair is black. Protein b (specified by the b allele) deposits eumelanin less densely, producing brown hair (chocolate). Allele B is dominant to allele b . Gene D specifies another protein that is also required for pigment deposition. The recessive allele d 1 specifies a protein that functions less efficiently than that specified by the dominant allele D . Less pigment is deposited in d 1 d 1 homozygous dogs than in dogs with a D allele, and so the color dictated by gene B is lighter. Which of the following genotypes would a light-chocolate dog have?  bbd 1 d 1