Sex determination in mammals is due to the SRY gene. Which of the following could allow a person with an XX karyotype to develop a male phenotype?

1. the loss of the SRY gene from an autosome
2. translocation of SRY to a X chromosome
3. a person with one normal and one shortened (deleted) X
4. a person with an extra autosomal chromosome

b

In humans, clear gender differentiation occurs, not at fertilization, but after the second month of gestation. What is the first event of this differentiation?

1. activation of SRY in females and feminization of the gonads
2. activation of SRY in male embryos and masculinization of the gonads
3. formation of estrogens in female embryos
4. formation of testosterone in male embryos

b

A geneticist did a testcross with an organism that had been found to be heterozygous for the three recessive traits and she was able to identify progeny of the following phenotypic distribution (+ = wild type): Which of the progeny phenotypes will require recombination between genes A and B?

1. 2, 4, 5, and 8
2. 1, 3, 6, and 7
3. 1, 2, 5, and 6
4. 2, 3, 5, and 7

c

A recessive allele on the X chromosome is responsible for red-green color blindness in humans. A woman with normal vision whose father is color blind marries a color-blind male. What is the probability that this couple's first son will be color blind?

1. 3/4
2. 2/3
3. 1/2
4. ¼

c

Sturtevant provided genetic evidence for the existence of four pairs of chromosomes in Drosophila in which of these ways?

1. The overall number of genes in Drosophila is a multiple of four.
2. There are four major functional classes of genes in Drosophila.
3. Drosophila genes have, on average, four different alleles.
4. Drosophila genes cluster into four distinct groups of linked genes.

d

Which of the following is an example of monosomy?

1. Down syndrome
2. Klinefelter's syndrome
3. Turner's syndrome
4. trisomy X

c

Of the following human aneuploidies, which is the one that generally has the most severe impact on the health of the individual?

1. 47, XXY
2. 45, X
3. 47, XXX
4. 47, trisomy 21

d

One possible result of chromosomal breakage is for a fragment to join a nonhomologous chromosome. What is this alteration called?

1. inversion
2. translocation
3. duplication
4. deletion

b

In birds, sex is determined by a ZW chromosome scheme that is much like the typical XY scheme seen in humans and many other organisms, except that the system is reversed: Males are ZZ (similar to XX in humans) and females are ZW (similar to XY in humans). A lethal recessive allele that causes death of the embryo occurs on the Z chromosome in pigeons. What would be the sex ratio in the offspring of a cross between a male heterozygous for the lethal allele and a normal female?

1. 3:1 male to female
2. 1:1 male to female
3. 2:1 male to female
4. 1:2 male to female

c

Recombination between linked genes comes about for what reason?

1. Nonrecombinant chromosomes break and then rejoin with one another.
2. Linked genes travel together at anaphase.
3. Independent assortment sometimes fails.
4. Crossovers between these genes result in chromosomal exchange.

d

Normally, only female cats have the tortoiseshell phenotype because _____.

1. multiple crossovers on the Y chromosome prevent orange pigment production
2. a male inherits only one allele of the X-linked gene controlling hair color
3. the Y chromosome has a gene blocking orange coloration
4. only males can have Barr bodies

b

A geneticist did a testcross with an organism that had been found to be heterozygous for the three recessive traits and she was able to identify progeny of the following phenotypic distribution (+ = wild type): What is the greatest benefit of having used a testcross for this experiment?

1. The phenotypes of the progeny reveal the allelic content of the gamete from the heterozygous parent.
2. The homozygous recessive parents are obvious to the naked eye.
3. The homozygous parents are the only ones whose crossovers make a difference.
4. All of the progeny will be heterozygous.

a

Correns found that the inheritance of variegated color on the leaves of certain plants was determined only by the maternal parent. What phenomenon explains this pattern?

1. chloroplast inheritance
2. sex-linkage
3. ribosome structure
4. genomic imprinting

a

All female mammals have one active X chromosome per cell instead of two. What causes this?

1. attachment of methyl (CH3) groups to the X chromosome that will remain active
2. inactivation of the XIST gene on the X chromosome derived from the male parent
3. activation of the XIST gene on the X chromosome that will become the Barr body
4. activation of the BARR gene on one X chromosome, which then becomes inactive

c

What is an adaptive advantage of recombination between linked genes?

1. Recombination must occur or genes will not assort independently.
2. New allele combinations are acted upon by natural selection.
3. Recombination is required for independent assortment.
4. The forces on the cell during meiosis II results in recombination.

b

A man who is an achondroplastic dwarf with normal vision marries a color-blind woman of normal height. The man's father was six 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. What proportion of their sons would be color-blind and of normal height?

1. all
2. half
3. none
4. one out of four

b

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 twenties. How likely is it for a woman to have this condition?

1. Women can never have this condition.
2. One-half of the daughters of an affected father and a carrier mother could have this condition.
3. One-fourth of the daughters of an affected man would have this condition.
4. Only if a woman is XXX could she have this condition.

b

In a Drosophila experiment, a cross was made between homozygous wild-type females and yellow-bodied males. All of the resulting F1s were phenotypically wild type. However, adult flies of the F2 generation (resulting from matings of the F1s) had the characteristics shown in the figure above. Consider the following questions:

(a) Is the mutant allele for yellow body recessive or dominant?

(b) Is the yellow locus autosomal (not X-linked) or X-linked?

1. (a) dominant; (b) X-linked
2. (a) recessive; (b) X-linked
3. (a) dominant; (b) not X-linked
4. (a) recessive; (b) not X-linked

b

A geneticist did a testcross with an organism that had been found to be heterozygous for the three recessive traits and she was able to identify progeny of the following phenotypic distribution (+ = wild type): The greatest distance among the three genes is between a and c. What does this mean?

1. Genes are in the order: a—b—c.
2. Gene a is between b and c.
3. Gene a is not recombining with c.
4. Gene c is between a and b.

a

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?

1. 0%
2. 50%
3. 25%
4. 100%

d

Which of the following statements is true of linkage?

1. All of the traits that Mendel studied—seed color, pod shape, flower color, and others—are due to genes linked on the same chromosome.
2. Linked genes are found on different chromosomes.
3. The observed frequency of recombination of two genes that are far apart from each other has a maximum value of 100%.
4. The closer two genes are on a chromosome, the lower the probability that a crossover will occur between them.

d

Which of the following is known as a Philadelphia chromosome?

1. a chromosome found only in mitochondria
2. a human chromosome 22 that has had a specific translocation
3. a human chromosome 9 that is found only in one type of cancer
4. an animal chromosome found primarily in the mid-Atlantic area of the United States

b

In Drosophila melanogaster, vestigial wings are caused by a recessive allele of a gene that is linked to a gene with a recessive allele that causes black body color. Morgan crossed black-bodied, normal-winged females and gray-bodied, vestigial-winged males. The F1 were all gray bodied, normal winged. The F1 females were crossed to homozygous recessive males to produce testcross progeny. Morgan calculated the map distance to be 17 map units. Which of the following is correct about the testcross progeny?

1. gray-bodied, normal-winged flies PLUS black-bodied, vestigial-winged flies = 17% of the total
2. black-bodied, normal-winged flies = 17% of the total
3. black-bodied, normal-winged flies PLUS gray-bodied, vestigial-winged flies = 17% of the total
4. black-bodied, vestigial-winged flies = 17% of the total

a

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?

1. expression of inappropriate gene products
2. failure of the cancer cells to multiply
3. a decrease in mitotic frequency
4. an increase in nondisjunction

a

What is a syndrome?

1. a characteristic facial appearance
2. a trait that leads to cancer at some stage in life
3. a specific characteristic that appears in conjunction with one specific aneuploidy
4. a group of traits typically found in conjunction with a particular chromosomal aberration or gene mutation

d

SRY is best described as _____.

1. an autosomal gene that is required for the expression of genes on the Y chromosome
2. a gene region present on the Y chromosome that triggers male development
3. an autosomal gene that is required for the expression of genes on the X chromosome
4. a gene present on the X chromosome that triggers female development

b

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?

1. The gene involved is on an autosome, but only in males.
2. The gene involved is on the X chromosome.
3. The gene involved is on the Y chromosome.
4. Other male-specific factors influence eye color in flies.

b

Males are more often affected by sex-linked traits than females because _____.

1. males are hemizygous for the X chromosome
2. female hormones such as estrogen often compensate for the effects of mutations on the X chromosome
3. male hormones such as testosterone often alter the effects of mutations on the X chromosome
4. X chromosomes in males generally have more mutations than X chromosomes in females

a

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?

1. 3:1 male to female
2. 1:1 male to female
3. 2:1 male to female
4. 1:2 male to female

c

Which of the following is the meaning of the chromosome theory of inheritance as expressed in the early twentieth century?

1. Natural selection acts on certain chromosome arrays rather than on genes.
2. No more than a single pair of chromosomes can be found in a healthy normal cell.
3. Individuals inherit particular chromosomes attached to genes.
4. Mendelian genes are at specific loci on the chromosome and, in turn, segregate during meiosis.

d

Normally, only female cats have the tortoiseshell phenotype because _____.

1. multiple crossovers on the Y chromosome prevent orange pigment production
2. a male inherits only one allele of the X-linked gene controlling hair color
3. the Y chromosome has a gene blocking orange coloration
4. only males can have Barr bodies

b

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?

1. tortoiseshell females; tortoiseshell males
2. orange females; black males
3. black females; orange males
4. tortoiseshell females; black males

d

Pseudohypertrophic muscular dystrophy is a human disorder that causes gradual deterioration of the muscles. Only boys are affected, and they are always born to phenotypically normal parents. Due to the severity of the disease, the boys die in their teens. Is this disorder likely to be caused by a dominant or recessive allele? Is its inheritance sex-linked or autosomal?

1. recessive, sex-linked
2. incomplete dominant, sex-linked
3. dominant, sex-linked
4. recessive, autosomal

a

Mitochondrial DNA is primarily involved in coding for proteins needed for protein complexes of the electron transport chain and ATP synthase. Therefore, mutations in mitochondrial genes would most affect _____.

1. DNA synthesis in cells of the immune system
2. the storage of urine in the urinary bladder
3. generation of ATP in muscle cells
4. the movement of oxygen into erythrocytes

c

A geneticist did a testcross with an organism that had been found to be heterozygous for the three recessive traits and she was able to identify progeny of the following phenotypic distribution (+ = wild type): If recombination frequency is equal to distance in map units, what is the approximate distance between genes A and B?

1. 3 map units
2. 6 map units
3. 30 map units
4. 15 map units

a

Genomic imprinting is generally due to the addition of methyl (—CH3) groups to C nucleotides and chemical histone changes to silence a given gene. If this depends on the sex of the parent who transmits the gene, which of the following must be true?

1. The imprints are transmitted only to gamete-producing cells.
2. Methylation of this kind must occur more in males than in females.
3. Methylation must be reversible in ovarian and testicular cells.
4. Genes required for early development stages must not be imprinted.

c

Between which two genes would you expect the highest frequency of recombination?

1. A and G
2. A and E
3. E and G
4. A and W

a

A woman is found to have forty-seven chromosomes, including three X chromosomes. Which of the following describes her expected phenotype?

1. a sterile female
2. healthy female of slightly above-average height
3. a female with masculine characteristics such as facial hair
4. an apparent male who is sterile

b

How would one explain a testcross involving F1 dihybrid flies in which more parental-type offspring than recombinant-type offspring are produced?

1. Recombination did not occur in the cell during meiosis.
2. The two genes are closely linked on the same chromosome.
3. Both of the characters are controlled by more than one gene.
4. The two genes are linked but on different chromosomes.

b

Glucose-6-phosphate dehydrogenase deficiency (G6PD) is inherited as a recessive allele of an X-linked gene 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 was not normal but was G6PD deficient, would you change your answer in part (a)?

1. (a) zero; (b) no
2. (a) 1/2; (b) yes
3. (a) 100%; (b) no
4. (a) 1/2; (b) no

d

A homozygous tomato plant with red fruit and yellow flowers was crossed with a homozygous tomato plant with golden fruit and white flowers. The F1 all had red fruit and yellow flowers. The F1 were testcrossed by crossing them to homozygous recessive individuals and the following offspring were obtained:

Red fruit and yellow flowers—41

Red fruit and white flowers—7

Golden fruit and yellow flowers—8

Golden fruit and white flowers—44

How many map units separate these genes?

1. 15
2. 17.6
3. 17.1
4. 18.1

a

What does a frequency of recombination of 50% indicate?

1. Abnormal meiosis has occurred.
2. All of the offspring have combinations of traits that match one of the two parents.
3. The genes are located on sex chromosomes.
4. The two genes are likely to be located on different chromosomes.

d

In a series of mapping experiments, the recombination frequencies for four different linked genes of Drosophila were determined as shown in the figure above. What is the order of these genes on a chromosome map?

1. B-rb-cn-vg
2. Vg-cn-b-rb
3. Cn-rb-b-vg
4. rb-cn-vg-b

a

A certain kind of snail can have a right-handed direction of shell coiling (DD or Dd) or left-handed coiling (dd). However, if direction of coiling is due to a protein deposited by the mother in the egg cytoplasm, then a Dd egg-producing snail and a dd sperm-producing snail will have offspring of which genotype(s) and phenotype(s)?

1. all Dd; half right-coiling and half left-coiling
2. 1/2 Dd:1/2 dd; all right-coiling
3. all Dd; all right-coiling
4. 1/2 Dd:1/2 dd; half right-coiling and half left-coiling

b

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?

1. Two of the four gametes descended from cell X will be haploid, and two will be diploid.
2. Half of the gametes descended from cell X will be n + 1, and half will be n - 1.
3. 1/4 of the gametes descended from cell X will be n + 1, 1/4 will be n - 1, and 1/2 will be n.
4. All the gametes descended from cell X will be diploid.

c

What is the definition of one map unit?

1. the recombination frequency between two genes assorting independently
2. 1 nanometer of distance between two genes
3. the physical distance between two linked genes
4. a 1% frequency of recombination between two genes

d

Map units on a linkage map cannot be relied upon to calculate physical distances on a chromosome for which of the following reasons?

1. The frequency of crossing over varies along the length of the chromosome.
2. Physical distances between genes change during the course of the cell cycle.
3. The relationship between recombination frequency and map units is different in every individual.
4. The gene order on the chromosomes is slightly different in every individual.

a

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?

1. The woman inherited this tendency from her parents.
2. The mother had a chromosomal duplication.
3. The mother most likely underwent nondisjunction during gamete production.
4. One member of the couple underwent nondisjunction in somatic cell production.

c