Chapter 15 Flashcards
1) When Thomas Hunt Morgan crossed his red-eyed F1 generation flies to each other, the F2 generation included both red- and white-eyed flies. Remarkably, all the white-eyed flies were male. What was the explanation for this result?
A) The gene involved is on the Y chromosome.
B) The gene involved is on the X chromosome.
C) The gene involved is on an autosome, but only in males.
D) Other male-specific factors influence eye color in flies.
E) Other female-specific factors influence eye color in flies.
B) The gene involved is on the X chromosome.
2) Sturtevant provided genetic evidence for the existence of four pairs of chromosomes in Drosophila in which of these ways?
A) There are four major functional classes of genes in Drosophila.
B) Drosophila genes cluster into four distinct groups of linked genes.
C) The overall number of genes in Drosophila is a multiple of four.
D) The entire Drosophila genome has approximately 400 map units.
E) Drosophila genes have, on average, four different alleles.
B) Drosophila genes cluster into four distinct groups of linked genes.
3) Which of the following is the meaning of the chromosome theory of inheritance as expressed in the early 20th century?
A) Individuals inherit particular chromosomes attached to genes.
B) Mendelian genes are at specific loci on the chromosome and in turn segregate during meiosis.
C) Homologous chromosomes give rise to some genes and crossover chromosomes to other genes.
D) No more than a single pair of chromosomes can be found in a healthy normal cell.
E) Natural selection acts on certain chromosome arrays rather than on genes.
B) Mendelian genes are at specific loci on the chromosome and in turn segregate during meiosis.
4) Thomas Hunt Morgan’s choice of Drosophila melanogaster has been proven to be useful even today. Which of the following has/have continued to make it a most useful species?
I. its four pairs of chromosomes
II. a very large number of visible as well as biochemically mutant phenotypes
III. easy and inexpensive maintenance
IV. short generation time and large number of offspring
A) I and IV only B) II and III only C) I, II, and III only D) II, III, and IV only E) I, II, III, IV, and V
E) I, II, III, IV, and V
5) A woman is found to have 47 chromosomes, including three X chromosomes. Which of the following describes her expected phenotype?
A) masculine characteristics such as facial hair
B) enlarged genital structures
C) excessive emotional instability
D) normal female
E) sterile female
D) normal female
6) Males are more often affected by sex-linked traits than females because
A) male hormones such as testosterone often alter the effects of mutations on the X chromosome.
B) female hormones such as estrogen often compensate for the effects of mutations on the X chromosome.
C) X chromosomes in males generally have more mutations than X chromosomes in females.
D) males are hemizygous for the X chromosome.
E) mutations on the Y chromosome often worsen the effects of X-linked mutations.
D) males are hemizygous for the X chromosome.
7) SRY is best described in which of the following ways?
A) a gene present on the X chromosome that triggers female development
B) an autosomal gene that is required for the expression of genes on the Y chromosome
C) a gene region present on the Y chromosome that triggers male development
D) an autosomal gene that is required for the expression of genes on the X chromosome
E) a gene required for development, and males or females lacking the gene do not survive past early childhood
C) a gene region present on the Y chromosome that triggers male development
8) In cats, black fur color is caused by an X-linked allele; the other allele at this locus causes orange color. The heterozygote is tortoiseshell. What kinds of offspring would you expect from the cross of a black female and an orange male?
A) tortoiseshell females; tortoiseshell males
B) black females; orange males
C) orange females; orange males
D) tortoiseshell females; black males
E) orange females; black males
D) tortoiseshell females; black males
9) Red-green color blindness is a sex-linked recessive trait in humans. Two people with normal color vision have a color-blind son. What are the genotypes of the parents? A) XcXc and XcY B) XcXc and XCY C) XCXC and XcY D) XCXC and XCY E) XCXc and XCY
E) XCXc and XCY
10) Cinnabar eyes is a sex-linked recessive characteristic in fruit flies. If a female having cinnabar eyes is crossed with a wild-type male, what percentage of the F1 males will have cinnabar eyes? A) 0% B) 25% C) 50% D) 75% E) 100%
E) 100%
11) Calico cats are female because
A) the males die during embryonic development.
B) a male inherits only one of the two X-linked genes controlling hair color.
C) the Y chromosome has a gene blocking orange coloration.
D) only females can have Barr bodies.
E) multiple crossovers on the Y chromosome prevent orange pigment production.
B) a male inherits only one of the two X-linked genes controlling hair color.
12) In birds, sex is determined by a ZW chromosome scheme. Males are ZZ and females are ZW. A recessive lethal allele that causes death of the embryo is sometimes present on the Z chromosome in pigeons. What would be the sex ratio in the offspring of a cross between a male that is heterozygous for the lethal allele and a normal female? A) 2:1 male to female B) 1:2 male to female C) 1:1 male to female D) 4:3 male to female E) 3:1 male to female
A) 2:1 male to female
13) Sex determination in mammals is due to the SRY region of the Y chromosome. An abnormality of this region could allow which of the following to have a male phenotype?
A) Turner syndrome, 45, X
B) translocation of SRY to an autosome of a 46, XX individual
C) a person with an extra X chromosome
D) a person with one normal and one shortened (deleted) X
E) Down syndrome, 46, XX
B) translocation of SRY to an autosome of a 46, XX individual
14) In humans, clear gender differentiation occurs, not at fertilization, but after the second month of gestation. What is the first event of this differentiation?
A) formation of testosterone in male embryos
B) formation of estrogens in female embryos
C) anatomical differentiation of a penis in male embryos
D) activation of SRY in male embryos and masculinization of the gonads
E) activation of SRY in females and feminization of the gonads
D) activation of SRY in male embryos and masculinization of the gonads
15) Duchenne muscular dystrophy (DMD) is caused by a gene on the human X chromosome. The patients have muscles that weaken over time because they have absent or decreased dystrophin, a muscle protein. They rarely live past their 20s. How likely is it for a woman to have this condition?
A) Women can never have this condition.
B) One-half of the daughters of an affected man could have this condition.
C) One-fourth of the children of an affected father and a carrier mother could have this condition.
D) Very rarely would a woman have this condition; the condition would be due to a chromosome error.
E) Only if a woman is XXX could she have this condition.
D) Very rarely would a woman have this condition; the condition would be due to a chromosome error.
16) Women (and all female mammals) have one active X chromosome per cell instead of two. What causes this?
A) modification of the XIST gene so that it is active only on one X chromosome, which then becomes inactive
B) activation of the Barr gene on one of the two X chromosomes that then inactivates
C) crossover between the XIST gene on one X chromosome and a related gene on an autosome
D) inactivation of the XIST gene on the X chromosome derived from the male parent
E) the removal of methyl (CH3) groups from the X chromosome that will remain active
A) modification of the XIST gene so that it is active only on one X chromosome, which then becomes inactive
17) Which of the following statements is true of linkage?
A) The closer two genes are on a chromosome, the lower the probability that a crossover will occur between them.
B) The observed frequency of recombination of two genes that are far apart from each other has a maximum value of 100%.
C) All of the traits that Mendel studied–seed color, pod shape, flower color, and others–are due to genes linked on the same chromosome.
D) Linked genes are found on different chromosomes.
E) Crossing over occurs during prophase II of meiosis.
A) The closer two genes are on a chromosome, the lower the probability that a crossover will occur between them.
18) How would one explain a testcross involving F1 dihybrid flies in which more parental-type offspring than recombinant-type offspring are produced?
A) The two genes are closely linked on the same chromosome.
B) The two genes are linked but on different chromosomes.
C) Recombination did not occur in the cell during meiosis.
D) The testcross was improperly performed.
E) Both of the characters are controlled by more than one gene.
A) The two genes are closely linked on the same chromosome.
19) What does a frequency of recombination of 50% indicate?
A) The two genes are likely to be located on different chromosomes.
B) All of the offspring have combinations of traits that match one of the two parents.
C) The genes are located on sex chromosomes.
D) Abnormal meiosis has occurred.
E) Independent assortment is hindered.
A) The two genes are likely to be located on different chromosomes.
20) What is the reason that linked genes are inherited together?
A) They are located close together on the same chromosome.
B) The number of genes in a cell is greater than the number of chromosomes.
C) Chromosomes are unbreakable.
D) Alleles are paired together during meiosis.
E) Genes align that way during metaphase I of meiosis.
A) They are located close together on the same chromosome.
