Exam 2 Flashcards

Hemophilia is caused by several genetic factors, one, a sex-linked recessive gene is the subject of this problem. Assume that a man with hemophilia marries a normal woman whose father had hemophilia. What is the probability that they will have a daughter with hemophilia? (note: in this problem you must include the probability of having a daughter in your computation of the final probability)

1. 1/4
2. 1/16
3. 1/2
4. 1/8
5. 3/4

Sex-influenced genes are those which cause males to be males and females to be females.

1. True
2. False

Normally in dogs, all the sons of a male showing a sex-linked phenotype will inherit the trait.

1. True
2. False

In a Drosophila experiment, a cross was made between homozygous wild type females and yellow-bodied males. All of the resulting F1's were phenotypically wild type. However, adult flies of the F2 generation (resulting from matings of the F1's) had the following characteristics:

Sex Phenotype Number

male wild 123

male yellow 116

female wild 240

(a) Is the mutant gene for yellow body recessive or dominant?
(b) Is the yellow locus autosomal (not sex-linked) or sex-linked?

1. recessive, not sex linked
2. dominant, sex linked
3. dominant, not sex linked
4. recessive, sex linked
5. none of these

A man who carries an X-linked mutant allele (gene) will pass it on to

1. all of his daughters.
2. all of his sons.
3. half of his sons.
4. all of his children.
5. half of his daughters.

Klinefelter syndrome in humans, which leads to underdeveloped testes and sterility, is caused by which chromosomal condition?

1. 47, XYY
2. 45, X
3. 47, XXY
4. 47, 21+
5. triploidy

In Drosophila, sex is determined by a balance between the number of haploid sets of autosomes and the number of ________.

1. centromeres
2. Y chromosomes
3. telomeres
4. nucleolar organizers
5. X chromosomes

In humans, the genetic basis for determining the sex "male" is accomplished by the presence of ________.

1. multiple alleles scattered throughout the autosomes
2. high levels of estrogen
3. a balance between the number of X chromosomes and the number of haploid sets of autosomes
4. one X chromosome
5. a portion of the Y chromosome

An individual with Turner Syndrome has no Barr bodies.

1. True
2. False

In Drosophila, the female is the heterogametic sex.

1. True
2. False

Assume that two genes are 80 map units apart on chromosome II of Drosophila and that a cross is made between a doubly heterozygous female and a homozygous recessive male. What percent recombination would be expected in the offspring of this type of cross?

1. Impossible to determine. Not enough information was given.
2. 100
3. 8
4. 80
5. 50

Under what circumstance might two loci be on the same chromosome but behave as if independently assorting in crosses?

1. If there is a positive interference
2. If there is a complete linkage
3. If there is a negative interference
4. If the genes are very far apart
5. If the chromosome is very long

Assume that a cross is made between AaBb and aabb plants and that the offspring occur in the following numbers: 48 AaBb, 106 Aabb, 94 aaBb, 52 aabb. These results are consistent with what arrangement of genes?

1. Impossible to determine. Not enough information was given.
2. In the AaBb parent, genes A and B are on different chromosomes and assort independently.
3. In the AaBb parent, one homolog carries Ab and the other carries aB.
4. In the AaBb parent, the dominant alleles are on one homolog and the recessive alleles are on the other.

What relatively recent scientific advancement has made mapping by linkage or classical genetic mapping approaches virtually obsolete?

1. negative interference
2. the inclusion of the X and Y chromosome in SNP experiments
3. the use of synteny
4. positive interference
5. the genome sequence of a species

In the fruit fly, Drosophila melanogaster, a spineless (no wing bristles) female fly is mated to a male that is claret (dark eyes) and hairless (no thoracic bristles). Phenotypically wild-type F1 female progeny were mated to fully homozygous (mutant) males, and the following progeny (1000 total) were observed:
spineless 321
wild type 38
claret, spineless 130
claret 18
claret, hairless 309
hairless, claret, spineless 32
hairless 140
hairless, spineless 12

Which gene is in the middle?

1. hairless
2. Impossible to determine. Not enough information is given.
3. spineless
4. claret

Why does recombination between linked genes continue to occur?

1. Recombination must occur or genes will not assort independently.
2. The forces on the cell during meiosis II always result in recombination.
3. New allele combinations are acted upon by natural selection.
4. Without recombination there would be an insufficient number of gametes.
5. Recombination is a requirement for independent assortment.

Phenotypically wild-type F1 female Drosophila, whose mothers had light eyes (lt) and fathers had straw (stw) bristles, produced the following offspring when crossed to homozygous light-straw males:
light-straw 22
wild type 18
light 990
straw 970

Compute the map distance between the light and straw loci.

1. 0.4 map units
2. 40 map units
3. 20 map units
4. 4 map units
5. 2 map units

In a three-point mapping experiment, what general classes of offspring are expected (assuming crossovers occur)?

1. noncrossovers and double crossovers only
2. single crossovers only
3. noncrossovers, single crossovers, double crossovers
4. noncrossovers and single crossovers only
5. noncrossovers only

In Drosophila, the frequency of crossing over in males is higher than the frequency of crossing over in females.

1. True
2. False

The cross GE/ge X ge/ge produces the following progeny, GE/ge 404; ge/ge 396; gE/ge 97; Ge/ge 103. From these data one can conclude that the recombinant progeny are gE/ge and Ge/ge.

1. True
2. False

Positive interference occurs when a crossover in one region of a chromosome interferes with crossovers in nearby regions.

1. True
2. False

Assume that a cross is made between AaBb and aabb plants and the offspring occure in following numbers: 47 AaBb, 50 Aabb, 52 aaBb, 49 aabb. These results are consistent with the following circumstance:

1. independent assortment
2. alternation of generations
3. hemizygosity
4. incomplete dominance
5. complete linkage

The genes for mahogany eyes and ebony body are approximately 25 map units apart on chromosome III in Drosophila. Assume that a mahogany-eyed female was mated to an ebony-bodied male and that the resulting F1 phenotypically wild-type females were mated to mahogany, ebony males. Of 1000 offspring, what would be the expected phenotypes, and in what numbers would they be expected?

1. mahogany = 475; ebony = 475; wild-type = 25; mahogany-ebony = 25
2. mahogany = 250; ebony = 250; wild-type = 250; mahogany-ebony = 250
3. mahogany = 375; ebony = 375; wild-type = 125; mahogany-ebony = 125
4. mahogany = 125; ebony = 125; wild-type = 375; mahogany-ebony = 375
5. Impossible to determine. Not enough information given

If the frequency of parental ditypes is greater than the frequency of nonparental ditypes, then the genes in question are linked.

1. True
2. False

Assume that investigators crossed a strain of flies carrying the dominant eye mutation Lobe on the second chromosome with a strain homozygous for the second chromosome recessive mutations smooth abdomen and straw body. The F1 Lobe females were then backcrossed with homozygous smooth abdomen, straw body males, and the following phenotypes were observed:

smooth abdomen, straw body 820
Lobe 780
smooth abdomen, Lobe 42
straw body 58
smooth abdomen 148
Lobe, straw body 152

smooth abdomen, lobe, straw body 0

wild type 0
Give the distance between lobe and straw body

1. 15 map units
2. These loci assort independently
3. 50 map units
4. 5 map units

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

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

In Drosophila, assume that the gene for scute bristles (s) is located at map position 0.0 and that the gene for ruby eyes (r) is at position 15.0. Both genes are located on the X chromosome and are recessive to their wild-type alleles. A cross is made between scute-bristled females and ruby-eyed males. Phenotypically wild-type F1 females were then mated to homozygous double mutant males, and 1000 offspring were produced. Give the phenotypes and frequencies expected.

1. scute = 75; ruby = 75; wild type = 425; scute-ruby = 425
2. scute = 350; ruby = 350; wild type = 150; scute-ruby = 150
3. scute = 425; ruby = 425; wild-type = 75; scute-ruby = 75
4. scute = 150; ruby = 150; wild type = 350; scute-ruby = 350
5. Impossible to determine. Not enough information was given

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?

1. a person with one normal and one shortened (deleted) X
2. Down syndrome, 46, XX
3. Turner syndrome, 45, X
4. translocation of SRY to an autosome of a 46, XX individual
5. a person with an extra X chromosome

A pericentric inversion includes the centromere.

1. True
2. False

Women (and all female mammals) have one active X chromosome per cell instead of two. What causes this?

1. modification of the XIST gene so that it is active only on one X chromosome, which then becomes inactive
2. activation of the Barr gene on one of the two X chromosomes that then inactivates
3. the removal of methyl (CH3) groups from the X chromosome that will remain active
4. inactivation of the XIST gene on the X chromosome derived from the male parent
5. crossover between the XIST gene on one X chromosome and a related gene on an autosome

In general, inversion and translocation heterozygotes are as fertile as organisms whose chromosome are in the standard arrangement.

1. True
2. False

Individuals with familial Down syndrome are trisomic and have 47 chromosomes.

1. True
2. False

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. formation of estrogens in female embryos
3. anatomical differentiation of a penis in male embryos
4. activation of SRY in male embryos and masculinization of the gonads
5. formation of testosterone in male embryos

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?

1. XCXC and XCY
2. XCXC and XcY
3. XcXc and XCY
4. XcXc and XcY
5. XCXc and XCY

Trisomy 21 or Down syndrome occurs when there is a normal diploid chromosomal complement of 46 chromosomes plus one (extra) chromosome #21. Such individuals therefore have 47 chromosomes. While there is impaired fertility of both sexes, females are more likely to be fertile 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?

1. None of the offspring would be expected to have Down syndrome.
2. Two-thirds of the offspring would be expected to have Down syndrome.
3. All the children would be expected to have Down syndrome.
4. One half of the offspring will be expected to have Down syndrome.
5. One third of the offspring would be expected to have Down syndrome.

While 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 ________.

1. a maternal age effect
2. too many X chromosomes
3. an inversion involving chromosome #21
4. a translocation involving chromosome #21
5. a chromosomal aberration involving chromosome #1

A genomic condition which may be responsible for some forms of fragile-X syndrome as well as Huntington disease involves

1. multiple breakpoints fairly evenly dispersed along the X chromosome.
2. single translocations in the X chromosome.
3. various lengths of trinucleotide repeats.
4. F plasmids inserted into the FMR-1 gene.
5. multiple inversions in the X chromosome.

Assume a species has a diploid chromosome number of 52. The term applied to an individual with 78 chromosomes would be triploid.

1. True
2. False

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. 2:1 male to female
3. 1:2 male to female
4. 4:3 male to female
5. 1:1 male to female

Given that loci A and B in Drosophila are sex-linked and 20 map units apart, what phenotypic frequencies would you expect in male and female offspring resulting from the following crosses? (Assume that A and B are dominant to a and b, respectively.)

AaBb (dominant alleles on same chromosome) female × ab/Y male

1. Ab = 40; aB = 40; AB = 10; ab = 10 (sexes have the same phenotypes)
2. AB = 40; ab = 40; Ab = 10; aB = 10 (sexes have the same phenotypes)
3. all males = ab, all females = AB
4. all males = AB, all females = ab
5. all males Ab, all females = aB

Given that loci A and B in Drosophila are sex-linked and 20 map units apart, what phenotypic frequencies would you expect in male and female offspring resulting from the following crosses? (Assume that A and B are dominant to a and b, respectively.)

AaBb (dominant alleles on homologs) female × ab/Y male

1. Ab = 40; aB = 40; AB = 10; ab = 10 (both sexes have the same phenotypic ratios)
2. AB = 40; ab = 40; Ab = 10; aB = 10 (both sexes have the same phenotypic ratios)
3. all males = ab, all females = AB
4. all males = AB, all females = ab
5. all males Ab, all females = aB

Given that loci A and B in Drosophila are sex-linked and 20 map units apart, what phenotypic frequencies would you expect in male and female offspring resulting from the following crosses? (Assume that A and B are dominant to a and b, respectively.)

aabb female × AB/Y male (no crossing over in male Drosophila)

1. Ab = 40; aB = 40; AB = 10; ab = 10 (both sexes have the same phenotypic ratios)
2. AB = 40; ab = 40; Ab = 10; aB = 10 (both sexes have the same phenotypic ratios)
3. all males = ab, all females = AB
4. all males = AB, all females = ab
5. all males Ab, all females = aB

If two gene loci are on nonhomologous chromosomes, genes at these loci are expected to assort independently.

1. True
2. False

The accompanying figure is a pedigree of a fairly common human hereditary trait; the boxes represent males and the circles represent females. Filled in symbols indicate the abnormal phenotype. Given that one gene pair is involved,

Is the inheritance pattern X-linked or autosomal?

1. X-linked dominant
2. X-linked recessive
3. autosomal dominant
4. autosomal recessive
5. Impossible to determine. Not enough information given.

A small part of the human Y chromosome contains the gene that is responsible for determining maleness. What is the name of this gene?

1. sxl – sex lethal
2. sry - sex-determining region Y
3. sxy – sex-lethal region Y
4. dsl – dosage sex lethal
5. mls – maleness gene

A cross is made between a female calico cat and a male cat having the gene for black fur on his X chromosome. What fraction of the offspring would one expect to be calico?

1. 1/2
2. 1/8
3. 1/4
4. 2/3
5. 1/3

My calico cat had a litter of 10 kittens: two black males, three yellow males, two yellow females and three calico cats. Assuming there was only one father, what was his probable coat color?

1. calico
2. yellow
3. black
4. Impossible to determine. Not enough information given.

Give the sex of the following organisms assuming that the autosomes are present in the normal number:

Human Drosophila_______

XO_ ________________________________

1. Human female, Drosophila male
2. Human male, Drosophila female
3. Human female, Drosophila female
4. Human male, Drosophila male
5. Human female, Drosophila metafemale

Give the sex of the following organisms assuming that the autosomes are present in the normal number:

Human Drosophila___

XXY _ __________________________

1. Human female, Drosophila male
2. Human male, Drosophila female
3. Human female, Drosophila female
4. Human male, Drosophila male
5. Human female, Drosophila metafemale

What is meant by the term dicentric?

1. a chromosome without a centromere
2. a chromosome with two centromeres
3. a gene with two centromeres
4. a gene without a centromere
5. a homologous pair with only one centromere

Which of the following statemetns best describes Bar mutations in Drosophila melanogaster.

1. Bar mutations are caused by inversion in portions of the X chromosome
2. Bar mutations are caused by inversion in portions of the Y chromosome
3. Bar mutations are duplications in portions of one of the autosomes
4. Bar mutations are duplications in portions of the X chromosome
5. Bar mutations are duplications in portions of the Y chromosome