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Linkage and chromosomes

27 important questions on Linkage and chromosomes

You design Drosophila crosses to provide recombination data for gene a, which is located on the chromosome shown in the figure below. Gene a has recombination frequencies of 14% with the vestigial-wing locus and 26% with the brown-eye locus. Approximately where is a located along the chromosome?

about one-third of the distance from the vestigial-wing locus to the brown-eye locus

Which of these descriptions of the behavior of chromosomes during meiosis explains Mendel’s law of segregation?

The two alleles for each gene separate as homologous chromosomes move apart during anaphase I.

Which of these descriptions of the behavior of chromosomes during meiosis explains Mendel’s law of independent assortment?

The arrangement of each pair of homologous chromosomes on the metaphase plate during metaphase I is random with respect to the arrangements of other pairs.

The correct statement(s) about sex determination in animals:

The mechanism of sex determination varies with different animal species.

Imagine a human disorder that is inherited as a dominant, X-linked trait. How would the frequency of this disorder vary between males and females?

Females would display this disorder with greater frequency than males.

Gregor Mendel set up a dihybrid cross with one pea plant from the parental generation (P) producing round yellow peas and the other pea plant producing wrinkled green peas. The F2 generation included 315 plants producing round yellow peas, 108 with round green peas, 101 with wrinkled yellow peas, and 32 with wrinkled green peas. How would these results have differed if pea shape and pea color had been linked genes, located close together on the same chromosome?

The F2 generation would have included a higher percentage of pea plants producing round, yellow peas.

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.

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

The mother

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%

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.

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.

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.

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.

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.

The recombination frequency between two gene loci is __________.

greater as the distance between the two loci increases

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

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

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

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

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

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

independent alignment of homologous chromosomes during meiosis I, the exchange of alleles between homologous chromosomes during meiosis I and
random fertilization increasing the number of possible allele combinations in an individual

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

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.

What is a nondisjunction?

An error in cell division that causes homologous chromosomes or sister chromatids to move to the same side of the dividing cell

What kind of cell results when a diploid and a haploid gamete fuse during fertilization?

A triploid cell

Of the following chromosomal abnormalities, which type is most likely to be viable in humans?

Trisomy

If a diploid cell undergoes meiosis and produces two gametes with n + 1 chromosomes and two gametes with n− 1 chromosomes, what type of error occurred?

A nondisjunction error occurred in meiosis I, in which both members of a homologous pair migrated to the same pole of the cell.

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Linkage and chromosomes

27 important questions on Linkage and chromosomes

You design Drosophila crosses to provide recombination data for gene a, which is located on the chromosome shown in the figure below. Gene a has recombination frequencies of 14% with the vestigial-wing locus and 26% with the brown-eye locus. Approximately where is a located along the chromosome?

Which of these descriptions of the behavior of chromosomes during meiosis explains Mendel’s law of segregation?

Which of these descriptions of the behavior of chromosomes during meiosis explains Mendel’s law of independent assortment?

The correct statement(s) about sex determination in animals:

Imagine a human disorder that is inherited as a dominant, X-linked trait. How would the frequency of this disorder vary between males and females?

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

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

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?

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?

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?

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

The recombination frequency between two gene loci is __________.

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?

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

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

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

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

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 __________.

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?

What is a nondisjunction?

What kind of cell results when a diploid and a haploid gamete fuse during fertilization?

Of the following chromosomal abnormalities, which type is most likely to be viable in humans?

If a diploid cell undergoes meiosis and produces two gametes with n + 1 chromosomes and two gametes with n− 1 chromosomes, what type of error occurred?

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