Genetics Chapter 8: Chromosome Mutations: Variation in Number and Arrangement Practice Questions

9. The normally cultivated cotton plant is a tetraploid (52 chromosomes). How many chromosomes did the probable ancestral haploid genome have? A. 13 B. 26 C. 52 D. 104

A. 13 If the current cotton plant has a tetraploid number of 52, the ancestral haploid genome probably had 13 chromosomes.

6. Individuals with which autosomal trisomy survive to adulthood? A. Down syndrome B. cri du chat syndrome C. Patau syndrome D. Edwards syndrome

A. Down syndrome Individuals with Down syndrome most often survive to adulthood, and some live fulfilling lives.

19. Why would the transmission of Down syndrome due to a Robertsonian translocation be unaffected by the age of the mother? A. Down syndrome due to a Robertsonian translocation does not result from nondisjunction, which is affected by age. B. This statement is incorrect; the age of the mother does affect the transmission of Down syndrome due to Robertsonian translocations. C. Robertsonian translocations occur only in young mothers. D. Women with a Robertsonian translocation are infertile.

A. Down syndrome due to a Robertsonian translocation does not result from nondisjunction, which is affected by age. A Robertsonian translocation that causes Down syndrome occurs when a large part of chromosome 21 is translocated to chromosome 14. The translocation can be passed on to the gametes, and thus there is always a 1-in-4 chance that a gamete will form with two copies of chromosome 21.

3. Which term best describes an individual with Klinefelter syndrome? A. aneuploid B. triploid C. euploid D. polyploid

A. aneuploid An individual with Klinefelter syndrome has an extra X chromosome, and aneuploidy refers to the gain or loss of individual chromosomes, but not a complete set.

16. All of the following are correctly paired with their causative chromosomal aberration EXCEPT __________. A. fragile-X syndrome, deletion B. Down syndrome, Robertsonian translocation C. Huntington disease, duplication D. cri du chat syndrome, deletion

A. fragile-X syndrome, deletion Fragile-X syndrome is an example of a trinucleotide repeat disorder, which shows increasing severity with increased copy number of a specific three-base sequence.

10. How many chromosomes would be found in an allopolyploid plant if its parents had diploid numbers of 4 and 6, respectively? A. haploid number of 5 B. haploid number of 10 C. diploid number of 5 D. diploid number of 12

A. haploid number of 5 The parents contribute two and three chromosomes, respectively, to each of their gametes.

14. In Drosophila, male flies that are hemizygous for the Bar allele __________. A. have slit-shaped eyes B. have larger than normal eyes C. have no eyes D. are phenotypically normal

A. have slit-shaped eyes Male flies have only one copy of the X-linked Bar gene, so a fly hemizygous for the mutated gene has very small eyes.

4. The incidence of Down syndrome, also known as trisomy 21, increases with increasing maternal age. Which of the following errors most likely produces this condition? A. nondisjunction during either meiosis I or meiosis II in the female gamete B. nondisjunction during meiosis II in either the male or the female gamete C. nondisjunction during either meiosis I or meiosis II in the male gamete D. nondisjunction during meiosis I in either the male or the female gamete

A. nondisjunction during either meiosis I or meiosis II in the female gamete Nondisjunction during either meiosis I or meiosis II can produce a gamete that will result in a trisomic zygote. Since the incidence of Down syndrome increases with maternal age, it is likely that this error occurs in the female gamete.

11. Chromosomal aberrations may be characterized by all of the following EXCEPT __________. A. substituting one base for another B. translocations C. inversions D. chromosome loss

A. substituting one base for another Substituting one base for another is not classified as a chromosomal mutation.

7. What is the most frequent aneuploidy observed in aborted fetuses? A. 45,Y B. 45,X C. trisomy 21 D. 47, XXY

B. 45, X This is the most common aneuploidy in aborted fetuses and results in Turner syndrome if the fetus survives to term.

18. A child is born with Down syndrome. Analysis of his karyotype shows two 21st chromosomes, a single 14th chromosome, and an additional large chromosome about the size of chromosome number 3. Which of the following conclusions can be drawn from the karyotype? A. The karyotoype indicates a monosomy of chromosome 14. B. The large chromosome represents a Robertsonian fusion between chromosomes 21 and 14. C. There is too little chromosome 21 material. D. The large chromosome represents an extra chromosome 3.

B. The large chromosome represents a Robertsonian fusion between chromosomes 21 and 14. There was probably a fusion of chromosomes 21 and 14, because one of the 14 homologs is missing and a new long chromosome has been created.

20. In fragile-X syndrome, expansion from carrier status (55 to 230 repeats) to syndrome status (over 230 repeats) occurs __________. A. during transmission of the unstable chromosome from father to son B. during transmission from the mother C. in the embryo D. during transmission of an X chromosome from father to daughter

B. during transmission from the mother Expansion of the trinucleotide repeat occurs during transmission from the mother.

13. The hypothesis that gene duplication is essential to evolution is supported by the existence of __________. A. intercalary deletions B. gene families C. fragile sites D. inversions

B. gene families Gene families are genes that descended by duplication and variation from some ancestral gene. The protein products from members of the same family usually perform the same function.

17. In a nonreciprocal translocation, a segment of a chromosome is __________. A. exchanged with a segment from a different chromosome B. transferred to a different chromosome C. exchanged with an identical segment on a sister chromatid D. reversed 180 degrees

B. transferred to a different chromosome In a nonreciprocal translocation, there is not an exchange of material between the two chromosomes.

8. Chrysanthemums have a haploid chromosome number of 9. How many chromosomes are found in tetraploid chrysanthemum species? A. 9 B. 18 C. 36 D. 72

C. 36 A tetraploid chrysanthemum has four sets of 9 chromosomes, which equals 36 chromosomes.

1. Which of the following conditions is euploid? A. 2n + 3 B. 2n − 3 C. 3n D. 2n − 1

C. 3n This individual is triploid, in which three haploid sets of chromosomes are present.

15. What phenotype would be expected in balanced translocation heterozygotes in the absence of position effects? A. abnormal, because they lack some genetic material B. normal, even though they have too much genetic material C. normal, because they have a normal amount of genetic material D. abnormal, because they have too much genetic material

C. normal, because they have a normal amount of genetic material Balanced translocation heterozygotes have a normal amount of genetic material, but it is in a translocated configuration. As long as there are no position effects, these individuals can be phenotypically normal.

5. Which human aneuploid condition does NOT involve a sex chromosome? A. familial Down syndrome B. Turner syndrome C. trisomy 21 D. fragile-X syndrome

C. trisomy 21 Down syndrome is caused by trisomy of chromosome 21.

2. Which gametes will be produced in a human, if nondisjunction of chromosome 3 occurs during the second meiotic division? A. all haploid gametes B. two diploid gametes and two haploid gametes C. two normal haploid gametes, one gamete with two copies of chromosome 3, and one gamete with no copy of chromosome 3 D. all trisomic gametes

C. two normal haploid gametes, one gamete with two copies of chromosome 3, and one gamete with no copy of chromosome 3 If nondisjunction occurs during the second meiosis, the sister chromatids do not segregate properly.

12. Which of the following human genetic diseases is caused by a segmental deletion (partial monosomy)? A. Edwards syndrome B. fragile-X syndrome C. Turner syndrome D. cri du chat syndrome

D. cri du chat syndrome Cri du chat is caused by a deletion, or partial monosomy, of the short arm of chromosome 5.