Chapter 7 Sex Determination and Sex Chromosomes1) In Drosophila, sex is determined by a balance between the number of haploid sets of autosomes and the number of ________.A) telomeresB) centromeresC) X chromosomesD) Y chromosomesE) nucleolar organizersAnswer: CSection: 7.52) In humans, the genetic basis for determining the sex "male" is accomplished by the presence of ________.A) a portion of the Y chromosomeB) one X chromosomeC) a balance between the number of X chromosomes and the number of haploidsets of autosomesD) high levels of estrogenE) multiple alleles scattered throughout the autosomesAnswer: ASection: 7.33) Klinefelter syndrome in humans, which leads to underdeveloped testes and sterility, is caused by which chromosomal condition?A) 47, XXYB) 47, 21+C) 45, XD) 47, XYYE) triploidyAnswer: ASection: 7.34) The Protenor mode of sex determination is the ________.A) scheme based on F plasmids inserted into the FMR-1 geneB) XX/XO schemeC) XO/YY schemeD) hermaphroditic schemeE) scheme based on single translocations in the X chromosomeAnswer: BSection: 7.1, 7.21Copyright © 2012 Pearson Education, Inc.5) The Lygaeus mode of sex determination is the ________.A) XY/XX schemeB) XX/XO schemeC) XO/YY schemeD) hermaphroditic schemeE) scheme based on single translocations in the X chromosomeAnswer: ASection: 7.1, 7.26) The sex of birds, some insects, and other organisms is determined by a ZW chromosomal arrangement in which the males have like sex chromosomes (ZZ) and females are ZW (similar to XY in humans). Assume that a recessive lethal allele on the Z chromosome causes death of an embryo in birds. What sex ratio would result in the offspring if a cross were made between a male heterozygous for the lethal allele and a normal female?A) 4:1 male to femaleB) 2:1 male to femaleC) 3:1 male to femaleD) 1:2 male to femaleE) 1:1 male to femaleAnswer: BSection: 7.27) A recessive gene for red-green color blindness is located on the X chromosome in humans. Assume that a woman with normal vision (her father is color blind) marries a color-blind male. What is the likelihood that this couple's first son will be color blind?A) 0%B) 25%C) 50%D) 75%E) 100%Answer: CSection: 7.38) One form of hemophilia is caused by a sex-linked recessive gene. Assume that a man with hemophilia marries a phenotypically normal woman whose father had hemophilia. What is the probability that they will have a daughter with hemophilia? (Note: In this problem, you must include the probability of having a daughter in your computation of the final probability.)A) 1/16B) 1/8C) 1/4D) 1/2E) 3/4Answer: CSection: 7.32Copyright © 2012 Pearson Education, Inc.9) One form of hemophilia is caused by a sex-linked recessive gene. Assume that a man with hemophilia marries a phenotypically normal woman whose father had hemophilia. What is the probability that their first son will have hemophilia?A) 1/16B) 1/8C) 1/4D) 1/2E) 3/4Answer: DSection: 7.310) Assume that a man who carries an X-linked gene has children. Assuming normal meiosis andrandom combination of gametes, the man would pass this gene to ________.A) half of his daughtersB) all of his daughtersC) all of his sonsD) half of his sonsE) all of his childrenAnswer: BSection: 7.311) Assume that you are told that a particular organism, Drosophila, has the XO chromosome complement. You are also told that the autosomal complement is a normal 2n. You know that in humans the XO complement is female determining. Would you be correct in assuming that the Drosophila sex for XO is also female? Choose the answer that includes the correct explanation.A) Yes, because sex determination in humans and insects is essentially the same.B) No, sex determination in Drosophila is dependent on the presence or absence of the Y chromosome.C) No, the chromosomal basis for sex determination in Drosophila based on the balance betweenthe number of X chromosomes and haploid sets of autosomes.D) Yes, the presence of an X chromosome determines a female in both organisms.E) No, it takes two X chromosomes to produce a female in humans and a Y chromosome to produce a male in Drosophila.Answer: CSection: 7.612) For an individual with the XXY chromosomal composition, the expected number of Barr bodies in interphase cells is ________.A) variableB) oneC) twoD) threeE) zeroAnswer: BSection: 7.53Copyright © 2012 Pearson Education, Inc.13) Glucose-6-phosphate dehydrogenase (G6PD) deficiency is inherited as an X-linked recessivegene in humans. A woman whose father suffered from G6PD marries a normal man.(a) What proportion of their sons is expected to be G6PD?(b) If the husband were not normal, but were G6PD deficient, would you change your answer in part (a)?Answer: (a) 1/2 (b) noSection: 7.314) In Drosophila, an individual female fly was observed to be of the XXY chromosome complement (normal autosomal complement) and to have white eyes as contrasted with the normal red eye color of wild type. The female's father had red eyes, and the mother had white eyes. Knowing that white eyes are X-linked and recessive, present an explanation for the genetic and chromosomal constitution of the XXY, white-eyed individual. It is important that you state inwhich parent and at what stage the chromosomal event occurred that caused the genetic and cytogenetic abnormality.Answer: Nondisjunction could have occurred either at meiosis I or meiosis II in the mother, thusgiving the XwXwY complement in the offspring.Section: 7.615) In Drosophila, an individual female fly was observed to be of the XXY chromosome complement (normal autosomal complement) and to have white eyes as contrasted with the normal red eye color of wild type. The female's mother and father had red eyes. The mother, however, was heterozygous for the gene for white eyes. Knowing that white eyes are X-linked and recessive, present an explanation for the genetic and chromosomal constitution of the XXY, white-eyed individual. It is important that you state in which parent and at what stage the chromosomal event occurred that caused the genetic and cytogenetic abnormality.Answer: Nondisjunction would have occurred at meiosis II in the mother, thus giving the XwXwY complement in the offspring.Section: 7.616) A color-blind, chromatin-positive male child (one Barr body) has a maternal grandfather whowas color blind. The boy's mother and father are phenotypically normal. Construct and support (using appropriately labeled diagrams) a rationale whereby