Chapter 4 Extensions of Mendelian Genetics1) With incomplete dominance, a likely ratio resulting from a monohybrid cross would be ________.A) 3:3B) 1:2:2:4C) 1:2:1D) 9:3:3:1E) 3:1Answer: CSection: 4.32) A situation in which there are more than two alternative forms of a given gene would be called________.A) multiple allelesB) alternation of generationsC) codominanceD) incomplete dominanceE) hemizygosityAnswer: ASection: 4.53) A condition in which one gene pair masks the expression of a nonallelic gene pair is called ________.A) codominanceB) epistasisC) dominanceD) recessivenessE) additive allelesAnswer: BSection: 4.84) Typical ratios resulting from epistatic interactions in dihybrid crosses would be ________.A) 9:3:3:1, 1:2:1B) 1:1:1:1, 1:4:6:4:1C) 9:3:4, 9:7D) 1:2:2:4:1:2:1:2:1E) 3:1, 1:1Answer: CSection: 4.81Copyright © 2012 Pearson Education, Inc.5) With which of the following would hemizygosity most likely be associated?A) codominanceB) incomplete dominanceC) trihybrid crossesD) X-linked inheritanceE) sex-limited inheritanceAnswer: DSection: 4.116) A mutation in a gene often results in a reduction of the product of that gene. The term for this type of mutation is ________.A) codominanceB) incomplete dominanceC) gain of functionD) multiple allelismE) loss of function or null (in the case of complete loss)Answer: ESection: 4.17) Because of the mechanism of sex determination, males of many species can be neither homozygous nor heterozygous. Such males are said to be ________.A) dominantB) hemizygousC) recessiveD) complementaryE) None of the answers listed is correct.Answer: BSection: 4.118) Assume that a dihybrid cross (AaBb × AaBb) is made in which the gene loci are autosomal, independently assorting, and incompletely dominant. What phenotypic ratio would you expect from such a cross? Just provide the ratio, not the phenotypes.Answer: 1:2:1:2:4:2:1:2:1Section: 4.39) Many of the color varieties of summer squash are determined by several interacting loci: AA or Aa gives white, aaBB or aaBb gives yellow, and aabb produces green. Assume that two fully heterozygous plants are crossed. Give the phenotypes (with frequencies) of the offspring.Answer: 12 (white):3 (yellow):1 (green)Section: 4.82Copyright © 2012 Pearson Education, Inc.10) In mice, there is a set of multiple alleles of a gene for coat color. Four of those alleles are as follows:C = full color (wild)cch = chinchillacd = dilutionc = albinoGiven that the gene locus is not sex-linked and that each allele is dominant to those lower in the list, diagram the crosses indicated below and give the phenotypic ratios expected from each.(a) wild (heterozygous for dilution) × chinchilla (heterozygous for albino)(b) chinchilla (heterozygous for albino) × albinoAnswer: (a) Ccd × cchc ⇒ 2 full color:1 chinchilla:1 dilution(b) cchc × cc ⇒ 1 chinchilla:1 albinoSection: 4.511) A mutant gene that produces brown eyes (bw) is located on chromosome #2 of Drosophila melanogaster, whereas a mutant gene producing bright red eyes, scarlet (st), is located on chromosome #3. Phenotypically, wild-type flies (with dull red eyes), whose mothers had brown eyes and whose fathers had scarlet eyes, were mated. The 800 offspring possessed the following phenotypes: wild type (dull red), white, scarlet (bright red), and brown. Most of the 800 offspring had wild-type eyes, whereas those with white eyes were the least frequent.(a) Using standard symbolism, diagram the cross from the P generation (brown-eyed mothers scarlet-eyed fathers) and the F1 generation. Be certain to provide the alleles of the mutant genes.(b) From the information presented above, how many white-eyed flies would you expect in the F2 generation?Answer: (a) P bw/bw; st+/st+× bw+/bw+; st/stF1: bw+/bw; st+/st× bw+/bw; st+/st(b) 50Section: 4.83Copyright © 2012 Pearson Education, Inc.12) In the mouse, gene A allows pigmentation to be deposited in the individual coat hairs; its allele a prevents such deposition of pigment, resulting in an albino. Gene B gives agouti (wild-type fur); its allele b gives black fur.(a) Diagram the cross between a doubly heterozygous agouti mouse mated with a doubly homozygous recessive white mouse.(b) What would be the expected phenotypic ratio in the progeny?Answer: (a) AaBb × aabb(b) 1 (agouti):1 (black):2 (albino)Section: 4.813) The trait of medium-sized leaves in iris is determined by the genetic condition PP'. Plants with large leaves are PP, whereas plants with small leaves are P'P'. A cross is made between two plants each with medium-sized leaves. If they produce 80 seedlings, what would be the expected phenotypes, and in what numbers would they be expected? What is the term for this allelic relationship?Answer: 20 (large leaves), 40 (medium leaves), 20 (small leaves); incomplete dominanceSection: 4.414) The trait for medium-sized leaves in iris is determined by the genetic condition PP'. Plants with large leaves are PP, whereas plants with small leaves are P'P'. The trait for red flowers is controlled by the genes RR, pink by RR', and white by R'R'. A cross is made between two plants each with medium-sized leaves and pink flowers. If they produce 320 seedlings, what would be the expected phenotypes, and in what numbers would they be expected? Assume no linkage.Answer: 20 large, red40 medium, red20 small, red40 large, pink80 medium, pink40 small, pink20 large, white40 medium, white20 small, whiteSection: 4.44Copyright © 2012 Pearson Education, Inc.15) The following coat colors are known to be determined by alleles at one locus in horses:palomino = golden coat with lighter mane and tailcremello = almost whitechestnut = brownThe following table gives ratios obtained in matings of the above varieties:Cross Parents Offspring1 cremello × cremello all cremello2 chestnut × chestnut all chestnut3 cremello × chestnut all palomino4 palomino × palomino 1/4 = chestnut1/2 = palomino1/4 = cremelloAssign gene symbols for the genetic control of coat color on the basis of these data.Diagram the last two matings.Answer: C1C1 = cremello, C2C2 = chestnut, C1C2 = palomino(3) C1C1 × C2C2(4) C1C2 × C1C2Section: 4.516) What is meant by the term epistasis? Distinguish between epistasis and dominance. Do not use examples in answering this question.Answer: Epistasis refers to a gene (or genes) of one pair masking the expression of a gene (or genes) at a different locus. Dominance refers to the form