Chapter 15 BIO

Four genes (A, B, C, and D) are on the same chromosome. The recombination frequencies are as follows: A-B: 19%; B-C: 14%; A-C: 5%; B-D: 2%; A-D: 21%; C-D: 16%. Based on this information, which sequence of genes is correct?

ACBD

Which of the following results of Thomas Hunt Morgan's experiments with white-eyed mutant flies was unexpected in light of Mendelian genetics?

Among the F2 progeny, only males had white eyes. All of the females had red eyes.

Why did Morgan choose Drosophila for his genetics experiments? a. They have a long generation time. b. A single mating can produce many offspring. c. They have a large number of chromosomes. d. Drosophila chromosomes can be easily distinguishable under a light microscope. e. Both the second and fourth answers are correct.

Both the second and fourth answers are correct.

Consider a woman who is a carrier of a recessive X-linked allele for hemophilia. Which of the following possibilities could explain the presence of the hemophilia allele in her genotype?

Either her mother was a carrier or her father had hemophilia.

Why are individuals with an extra chromosome 21, which causes Down syndrome, more numerous than individuals with an extra chromosome 3 or chromosome 16?

Extra copies of the other chromosomes are probably fatal to the developing embryo.

It is proposed that a certain disorder affecting the inner ear is caused by mitochondrial DNA. Which of the following observations would be the most decisive evidence against this idea?

Fathers with the disorder pass it on to all their children, but mothers with the disorder do not pass it along.

If a woman is heterozygous for a recessive sex-linked allele and her husband has the dominant allele, which one of the following is true about the probabilities for their children?

Half of their sons will show the recessive trait.

A woman is red-green color-blind. What can we conclude, if anything, about her father?

He is red-green color-blind.

In a certain fish, fin rays (supporting structures for the fins) can be either bony or soft in adult fish. Sex linkage in a fish is similar to that in humans. What evidence would most strongly support the idea that the ray locus is on the X chromosome?

Matings of soft ray males and bony ray females give different results from the matings of bony ray males and soft ray females.

__________ is usually less severe than __________, and __________ species have been observed in plants, fish, amphibians, and even mammals.

Polyploidy ... aneuploidy ... polyploid

X-linked genes differ from Y-linked genes in which of the following ways?

Sons and daughters have equal probabilities in inheriting a recessive allele of an X-linked gene from their mother, but only sons can inherit rare Y-linked genetic disorders from their father.

Which of the following best describes the function of the XIST gene in X chromosome inactivation?

The XIST gene on the X chromosome that will be inactivated is expressed to produce multiple RNA transcripts that bind to that chromosome and effectively cover it up, thereby generating a Barr body.

Which of the following would result in genetic variation by way of new combinations of alleles?

The first three responses are correct.

The chromosome theory of inheritance states that __________. a. genes occupy specific positions on chromosomes b. homologous chromosomes segregate from each other during meiosis c. chromosomes assort independently during meiosis

The first, second, and third answers are correct.

In a particular species of mammal, black hair (B) is dominant to green hair (b), and red eyes (R) are dominant to white eyes (r). When a BbRr individual is mated with a bbrr individual, offspring are produced in a ratio of 5 black hair and red eyes:5 green hair and white eyes:1 black hair and white eyes:1 green hair and red eyes. The expected result would be equal numbers of these four phenotypes. Which of these explanations accounts for this ratio?

The genes for hair color and eye color are linked.

Duchenne muscular dystrophy is caused by a sex-linked recessive allele. Its victims are almost invariably boys, who usually die before the age of 20. Why is this disorder almost never seen in girls?

To express an X-linked recessive allele, a female must have two copies of the allele, one of which is contributed by the father.

The chromosomal abnormality in which a fragment of a chromosome breaks off and then reattaches to the original chromosome in the same place but in the reverse direction is called __________.

inversion

A person with two X chromosomes and one Y chromosome would appear to be __________.

male

Because the frequency of crossing over is not uniform along the length of a chromosome, __________.

map units do not necessarily correlate to physical distances along the chromosome

Individuals with an extra X chromosome __________.

may have subnormal intelligence or be at risk for learning disabilities

During meiosis, homologous chromosomes sometimes "stick together" and do not separate properly. This phenomenon is known as __________.

nondisjunction

In Klinefelter syndrome, individuals are phenotypically male, but they have reduced sperm production and may have some breast development in adolescence. The cells of Klinefelter individuals have two X chromosomes and one Y (they are XXY instead of XY). This occurs because of what meiotic error?

nondisjunction

A person's remains are found, and officials are trying to identify them. A couple believes that the remains belong to their missing daughter. Because the remains have decayed considerably, mitochondrial DNA is being used to determine the person's identity. In order to determine if the remains belong to someone in this couple's family, whose mitochondrial DNA should be used for comparison?

one of the couple's other children

A linkage map __________.

orders genes on a chromosome based on recombination frequencies

The Prenatally and Postnatally Diagnosed Conditions Awareness Act was enacted to __________.

require medical practitioners to provide up-to-date, evidence-based information to parents about any prenatal or postnatal diagnosis for a trisomy condition, and connect the parents with appropriate support services

Wild type refers to __________.

the most common phenotype thought to be found in the natural population

For an X-linked trait, it is the contribution of __________ that determines whether a son will display the trait.

the mother

If two genes are linked, __________.

they are on the same chromosome

Gene A is normally found on chromosome number 15 in humans. If amniocentesis reveals fetal cells containing gene A on chromosome 17, but not on 15, the best explanation would be that __________.

translocation occurred

You perform a testcross using F1 dihybrid flies. If, in the resulting offspring, the percentages of parental and recombinant offspring are about the same, this would indicate that the two genes are __________.

unlinked

A woman is a carrier for red-green color blindness, a sex-linked trait. Her husband is normal (not color-blind) for this trait. What are the chances that their newborn daughter will be red-green color-blind?

0%

What is the probability that a human male will inherit an X-linked recessive allele from his father?

0%

Hemophilia is an X-linked disorder. The daughter of a father with hemophilia and a carrier mother has a __________ probability of having hemophilia.

50%

In werewolves (hypothetically), the pointy ear allele (P) are dominant over the round ear allele (p). The gene for ear shape is on the X chromosome. (Sex determination in werewolves is the same as for "other" humans.) A certain female werewolf has pointy ears even though her father had round ears. What percentage of her sons will have round ears if she mates with a werewolf with round ears?

50%

A genetic defect in humans results in the absence of sweat glands in the skin. Some men have this defect all over their bodies, but in women it is usually expressed in a peculiar way: A woman with this defect typically has small patches of skin with sweat glands and other patches without sweat glands. In women, the pattern of sweat-gland distribution can best be explained by __________.

X chromosome inactivation

Which of the following is the only known viable human monosomy?

XO

Cells that have an abnormal number of some particular chromosome are said to be __________.

aneuploid

When a person has Down syndrome, he or she has an extra chromosome 21. Therefore, Down syndrome is a kind of __________ and results from __________.

aneuploidy ... nondisjunction of chromosome 21

In a particular species of mammal, black hair (B) is dominant to green hair (b), and red eyes (R) are dominant to white eyes (r). When a BbRr individual was mated with a bbrr individual, the observed distribution of offspring was as follows: black-red 1,070; black-white 177; green-red 180; green-white 1,072. Based on these data, what is the recombination frequency?

approximately 14%

A gray-bodied, vestigial-winged fly is crossed with a black-bodied, normal-winged fly. The F1 progeny is testcrossed. Among the resulting offspring, __________ is a parental type, and __________ is a recombinant type.

black-bodied, normal-winged ... black-bodied, vestigial-winged

What appears to be the mechanism for genomic imprinting?

both the first and third listed responses

Both chloroplasts and mitochondria __________.

carry extranuclear genes

Which type of chromosomal alteration is responsible for the cri du chat syndrome?

deletion

Genomic imprinting in mammals appears to affect primarily genes involved in __________.

embryonic development

The recombination frequency between two gene loci is __________.

greater as the distance between the two loci increases