Chapter 8 Chromosome Mutations: Variation in Number and Arrangement 1) The condition that exists when an organism gains or loses one or more chromosomes but not acomplete haploid set is known as ________.A) polyploidyB) euploidyC) aneuploidyD) triploidyE) trisomyAnswer: CSection: 8.12) The condition known as cri-du-chat syndrome in humans has a genetic constitution designatedas ________.A) 45, XB) heteroplasmyC) 46, 5p-D) triploidyE) trisomyAnswer: CSection: 8.53) Although the most frequent forms of Down syndrome are caused by a random error, nondisjunction of chromosome 21, Down syndrome occasionally runs in families. The cause of this form of familial Down syndrome is ________.A) an inversion involving chromosome 21B) a chromosomal aberration involving chromosome 1C) too many X chromosomesD) a translocation between chromosome 21 and a member of the D chromosome groupE) a maternal age effectAnswer: DSection: 8.84) A genomic condition that may be responsible for some forms of fragile-X syndrome, as well as Huntington disease, involves ________.A) F plasmids inserted into the FMR-1 geneB) various lengths of trinucleotide repeatsC) multiple breakpoints fairly evenly dispersed along the X chromosomeD) multiple inversions in the X chromosomeE) single translocations in the X chromosomeAnswer: BSection: 8.91Copyright © 2012 Pearson Education, Inc.5) Recently, a gene located on chromosome 3 in humans, FHIT, has been shown to be associated with the significant human malady known as ________.A) cancerB) Huntington diseaseC) "mad-cow" diseaseD) Klinefelter syndromeE) XYY/XY mosaicismAnswer: ASection: 8.96) Trisomy 21, or Down syndrome, occurs when there is a normal diploid chromosomal complement but one (extra) chromosome 21. Although fertility is reduced in both sexes, females have higher fertility rates than males. Van Dyke et al. (1995; Down Syndrome Research and Practice 3(2):65—69) summarize data involving children born of Down syndrome individuals. Assume that children are born to a female with Down syndrome and a normal 46-chromosome male. What proportion of the offspring would be expected to have Down syndrome?A) One-third of the offspring would be expected to have Down syndrome.B) Two-thirds of the offspring would be expected to have Down syndrome.C) All the children would be expected to have Down syndrome.D) None of the offspring would be expected to have Down syndrome.E) One-half of the offspring would be expected to have Down syndrome.Answer: ESection: 8.27) Trisomy 21, or Down syndrome, occurs when there is a normal diploid chromosomal complement but one (extra) chromosome 21. While there is reduced fertility in both sexes, females have higher fertility than males. Van Dyke et al. (1995; Down Syndrome Research and Practice 3(2):65—69) summarize data involving children born of Down syndrome individuals. Given the fact that conceptuses with 48 chromosomes (four #21 chromosomes) are not likely to survive early development, what percentage of surviving offspring would be expected to have Down syndrome if both parents have Down syndrome?A) One-third of the surviving offspring would be expected to have Down syndrome.B) All the children would be expected to have Down syndrome.C) None of the surviving offspring would be expected to have Down syndrome.D) Two-thirds of the surviving offspring would be expected to have Down syndrome.E) One-half of the surviving offspring would be expected to have Down syndrome.Answer: DSection: 8.28) What explanation is generally given for lethality of monosomic individuals?Answer: Monosomy may unmask recessive lethals that are tolerated in heterozygotes carrying the wild-type allele.Section: 8.22Copyright © 2012 Pearson Education, Inc.9) Describe the maternal age effect associated with Down syndrome.Answer: For unknown reasons, the nondisjunctional event that produces Down syndrome occursmore frequently during oogenesis in women older than age 35.Section: 8.210) Name two methods used in genetic prenatal diagnostic testing in humans.Answer: amniocentesis and chorionic villus sampling (CVS)Section: 8.211) Name the polyploid condition that is formed from the addition of one or more extra sets of chromosomes identical to the normal haploid complement of the same species.Answer: autotetraploidy, assuming the normal chromosome complement is diploidSection: 8.312) Colchicine is an alkaloid derived from plants. What is its effect on chromosome behavior?Answer: By interfering with spindle formation, replicated chromosomes fail to migrate to the poles at anaphase; thus, sister chromatids end up in the same nucleus.Section: 8.313) Deletions are chromosomal aberrations in which some portion of a chromosome is missing. Describe a method using Drosophila deletions to determine the actual, physical location of a gene.Answer: Crosshomozygous mutant flies to homozygous wild-type flies that have been irradiated(or those with a series of known deletions–see below). Select mutant flies in the F1. Those of the F1 that display the mutant phenotype may have resulted from the wild-type allele being deleted by the X-ray treatment. Establish a stock of the exceptional mutant fly; then examine polytene chromosomes in larvae. The mutation in question may be contained in the compensation loop in the homolog of the deleted chromosome. If a series of known deletions is available (and these doexist in stock centers throughout the world), one can test (by the mating described above) the mutation against each deletion. Obviously, this would be a very time-consuming task unless one had some prior knowledge as to the general location of the mutant gene. This can be accomplished using balancer chromosomes and standard linkage determination. Once the mutantgene is "exposed" by a given deletion, a series of additional deletions can be used to "fine map" the region and determine a fairly accurate location for the gene.Section: 8.53Copyright © 2012 Pearson Education, Inc.14) Inversion heterokaryotypes are often characterized as having reduced crossing over and reduced fertility. Assume that you were examining a strain of organisms you knew to be inversion heterokaryotypes and saw a relatively high number of double chromatid bridges extending between anaphase I nuclei. What would be a likely explanation for this observation? Explain with a labeled diagram.Answer: A four-strand double crossover in the inversion loop of a paracentric inversion (in the