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?
B) The gene involved is on the X chromosome.
2) Which of the following is the meaning of the chromosome theory of inheritance as expressed in the early 20th century?
B) Mendelian genes are at specific loci on the chromosome and in turn segregate during meiosis.
3) Males are more often affected by sex-linked traits than females because
D) males are hemizygous for the X chromosome.
4) SRY is best described in which of the following ways?
C) a gene region present on the Y chromosome that triggers male development
5) 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?
D) tortoiseshell females; black males
6) 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?
E) XNXn and XNY
7) 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?
E) 100%
8) Normally, only female cats have the tortoiseshell phenotype because
B) a male inherits only one allele of the X-linked gene controlling hair color.
9) 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?
B) translocation of SRY to an autosome of a 46, XX individual
10) In humans, clear gender differentiation occurs not at fertilization, but after the second month of gestation. What is the first event of this differentiation?
D) activation of SRY in male embryos and masculinization of the gonads
11) Duchenne muscular dystrophy is a serious condition caused by a recessive allele of 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?
D) Very rarely: it is rare that an affected male would mate with a carrier female.
12) All female mammals have one active X chromosome per cell instead of two. What causes this?
A) activation of the XIST gene on the X chromosome that will become the Barr body
13) 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.
14) 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.
15) What does a frequency of recombination of 50% indicate?
A) The two genes are likely to be located on different chromosomes.
16) Three genes (A, B, and C) at three loci are being mapped in a particular species. Each gene has two alleles, one of which results in a phenotype that is markedly different from the wild type. The unusual allele of gene A is inherited with the unusual allele of gene B or C about 50% of the time. However, the unusual alleles of genes B and C are inherited together 14.4% of the time.
Which of the following describes what is happening?
D) Gene A is assorting independently of genes B and C, which are linked.
17) What is one map unit equivalent to?
B) 1% frequency of recombination between two genes
18) Recombination between linked genes comes about for what reason?
D) Crossovers between these genes result in chromosomal exchange.
19) Why does recombination between linked genes continue to occur?
C) New allele combinations are acted upon by natural selection.
20) Map units on a linkage map cannot be relied upon to calculate physical distances on a chromosome for which of the following reasons?
A) The frequency of crossing over varies along the length of the chromosome.
21) What is the reason that closely linked genes are typically inherited together?
A) The likelihood of a crossover event between these two genes is low.
22) Sturtevant provided genetic evidence for the existence of four pairs of chromosomes in Drosophila in which of these ways?
B) Drosophila genes cluster into four distinct groups of linked genes.
23) If cell X enters meiosis, and nondisjunction of one chromosome occurs in one of its daughter cells during meiosis II, what will be the result at the completion of meiosis?
C) One-fourth of the gametes descended from cell X will be n + 1, 1/4 will be n - 1, and 1/2 will be n.
24) One possible result of chromosomal breakage is for a fragment to join a nonhomologous chromosome. What is this alteration called?
D) translocation
25) A nonreciprocal crossover causes which of the following products?
D) deletion and duplication
26) Of the following human aneuploidies, which is the one that generally has the most severe impact on the health of the individual?
A) 47, +21
27) A phenotypically normal prospective couple seeks genetic counseling because the man knows that he has a translocation of a portion of his chromosome 4 that has been exchanged with a portion of his chromosome 12. Although he is normal because his translocation is balanced, he and his wife want to know the probability that his sperm will be abnormal. What is your prognosis regarding his sperm?
A) One-fourth will be normal, 1/4 will have the translocation, and 1/2 will have duplications and deletions.
28) Abnormal chromosomes are frequently found in malignant tumors. Errors such as translocations may place a gene in close proximity to different control regions. Which of the following might then occur to make the cancer worse?
B) expression of inappropriate gene products
29) An inversion in a human chromosome often results in no demonstrable phenotypic effect in the individual. What else may occur?
B) Some abnormal gametes may be formed.
30) What is the source of the extra chromosome 21 in an individual with Down syndrome?
D) nondisjunction or translocation in either parent
31) Down syndrome has a frequency in the U.S. population of ~1/700 live births. In which of the following groups would you expect this frequency to be significantly higher?
E) No groups have such higher frequency.
32) A couple has a child with Down syndrome. The mother is 39 years old at the time of delivery. Which of the following is the most probable cause of the child's condition?
D) One member of the couple underwent nondisjunction in gamete production.
33) What is a syndrome?
C) a group of traits typically found in conjunction with a particular chromosomal aberration or gene mutation
34) Which of the following is known as a Philadelphia chromosome?
A) a human chromosome 22 that has had a specific translocation
35) At what point in cell division is a chromosome lost so that, after fertilization with a normal gamete, the result is an embryo with 45, X?
I. an error in anaphase I
II. an error in anaphase II
III. an error of the first postfertilization mitosis
IV. an error in pairing
E) I, II, III, or IV
36) Which of the following is true of aneuploidies in general?
B) 45, X is the only known human live-born monosomy.
37) A woman is found to have 47 chromosomes, including three X chromosomes. Which of the following describes her expected phenotype?
D) healthy female of slightly above-average height
A man who is an achondroplastic dwarf with normal vision marries a color-blind woman of normal height. The man's father was 6 feet tall, and both the woman's parents were of average height. Achondroplastic dwarfism is autosomal dominant, and red-green color blindness is X-linked recessive.
1) How many of their daughters might be expected to be color-blind dwarfs?
B) none
A man who is an achondroplastic dwarf with normal vision marries a color-blind woman of normal height. The man's father was 6 feet tall, and both the woman's parents were of average height. Achondroplastic dwarfism is autosomal dominant, and red-green color blindness is X-linked recessive.
2) What proportion of their sons would be color-blind and of normal height?
B) half
A man who is an achondroplastic dwarf with normal vision marries a color-blind woman of normal height. The man's father was 6 feet tall, and both the woman's parents were of average height. Achondroplastic dwarfism is autosomal dominant, and red-green color blindness is X-linked recessive.
3) They have a daughter who is a dwarf with normal color vision. What is the probability that she is heterozygous for both genes?
E) 100%