A white-eyed female Drosophila is crossed with a red-eyed male Drosophila. Which statement below correctly describes the results?
answer
None of the females will have white eyes.
All of the females will have red eyes because they will inherit the dominant red-eye allele from their male parent.
question
In humans, what determines the sex of offspring and why?
answer
The male gamete determines sex because each male gamete can contribute either an X or a Y chromosome.
In humans, the male produces both X- and Y-bearing sperm, whereas females only produce X-bearing eggs.
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Which of the following is true of an X-linked gene, but not of a Y-linked gene?
answer
The gene is present in both males and females.
All cells have at least one functional X chromosome.
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Males are more often affected by sex-linked traits than females because
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Males are hemizygous for the X chromosome.
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SRY is best described in which of the following ways?
answer
A gene region present on the Y chromosome that triggers male development
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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?
answer
XNXn and XNY
question
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?
answer
100%
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Which of the following statements is true of linkage?
answer
The closer two genes are on a chromosome, the lower the probability that a crossover will occur between them.
question
What is a nondisjunction?
answer
An error in cell division that causes homologous chromosomes or sister chromatids to move to the same side of the dividing cell
Nondisjunction refers to the failure of pairs of chromosomes or sister chromatids to separate during meiosis or mitosis.
question
When can nondisjunction occur?
answer
In mitosis, when sister chromatids fail to separate
In meiosis, when sister chromatids fail to separate
In meiosis, when homologous chromosomes fail to separate
Nondisjunction errors can occur in meiosis I, when homologous chromosomes fail to separate, or in either mitosis or meiosis II, when sister chromatids fail to separate.
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Which syndrome is characterized by the XO chromosome abnormality?
answer
Turner syndrome
Turner syndrome is characterized by a chromosome pattern of XO, or one X chromosome and no Y chromosome.
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What kind of cell results when a diploid and a haploid gamete fuse during fertilization?
answer
A triploid cell
A triploid cell has three sets of chromosomes: the two from the diploid gamete and the one from the haploid gamete.
question
Of the following chromosomal abnormalities, which type is most likely to be viable in humans?
answer
Trisomy
Some trisomies are viable in humans, but they result in developmental abnormalities, such as Down syndrome (trisomy 21). Only humans with trisomies of the small chromosomes (13, 18, or 21) or the sex chromosomes survive past birth.
question
If a diploid cell undergoes meiosis and produces two gametes that are normal, and one with n ? 1 chromosomes, and one with n + 1 chromosomes, what type of error occurred?
answer
A nondisjunction error occurred in meiosis II, in which both sister chromatids of a chromosome migrated to the same pole of the cell.
When this error occurs in meiosis II, only half of the gametes are affected.
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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?
answer
A nondisjunction error occurred in meiosis I, in which both members of a homologous pair migrated to the same pole of the cell.
When this type of error occurs, half of the gametes receive one too many chromosomes, and the other half receive one too few. When all of the gametes are affected, the error probably occurred in meiosis I.
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In general, the frequency with which crossing over occurs between two linked genes depends on what?
answer
how far apart they are on the chromosome
The farther apart two genes are, the greater the probability that a crossover will occur between them, and therefore the greater the recombination frequency.
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Normally, only female cats have the tortoiseshell phenotype because
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a male inherits only one allele of the X-linked gene controlling hair color.
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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?
answer
2:1 male to female
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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?
answer
translocation of SRY to an autosome of a 46, XX individual
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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.
How many of their daughters might be expected to be color-blind dwarfs?
answer
none
question
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.
What proportion of their sons would be color-blind and of normal height?
answer
half
question
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.
They have a daughter who is a dwarf with normal color vision. What is the probability that she is heterozygous for both genes?
answer
100%
question
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?
answer
Gene A is assorting independently of genes B and C, which are linked.
question
What is one map unit equivalent to?
answer
1% frequency of recombination between two genes
question
Recombination between linked genes comes about for what reason?
answer
Crossovers between these genes result in chromosomal exchange.
question
Which statement about recombination between linked genes is correct?
answer
New allele combinations may result in differential reproductive success.
question
Define deletion
answer
A deletion is the loss of part of a chromosomal segment.
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Define duplication
answer
A duplication is the repetition of a segment. The repeated segment may be located next to the original or at a different location, and its orientation may be the same as the original or the reverse.
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Define inversion
answer
An inversion is the removal of a segment followed by its reinsertion into the same chromosome in the reverse orientation.
question
Define translocation
answer
A translocation is the transfer of a segment to a nonhomologous chromosome. Translocations may be reciprocal (two nonhomologous chromosomes exchange segments) or nonreciprocal (one chromosome transfers a segment without receiving one).
question
Meiosis occurs normal (no disjunction)
answer
3 only
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Nondisjunction of one chromosome pair in meiosis I
answer
2 or 4
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Nondisjunction of all three chromosome pairs in meiosis I
answer
0 or 6
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Nondisjunction of one chromosome in one daughter cell in meiosis II
answer
2, 3, or 4
question
Nondisjunction of all three chromosomes in one daughter cell in meiosis II
answer
0, 3, or 6
question
Humans are diploid and have 46 chromosomes (or two sets). How many sets of chromosomes are found in each human gamete?
answer
1
Meiosis cuts the number of chromosomal sets in half.
question
Humans are diploid and have 46 chromosomes. How many chromosomes are found in each human gamete?
answer
23
23 is one-half of 46.
question
_____ is the process by which haploid gametes form a diploid zygote.
answer
Fertilization
The joining of haploid gametes produces a diploid zygote.
question
A particular diploid plant species has 48 chromosomes, or two sets. A mutation occurs and gametes with 48 chromosomes are produced. If self-fertilization occurs, the zygote will have _____ set(s) of chromosomes.
answer
4
If self-fertilization occurs, and two gametes (each having 48 chromosomes) unite, the zygote will have 96 chromosomes (or 4 sets).
question
Which of these terms applies to an organism with extra sets of chromosomes?
answer
polyploid
Polyploid individuals have more than two complete sets of chromosomes.
question
Mutant tetraploid plants _____.
answer
are unable to interbreed with a diploid plant
This is why polyploidy is a mechanisms of plant speciation.
question
Most polyploid plants arise as a result of _____.
answer
hybridization
Most polyploid plants are the result of the hybridization of two different parental species.
question
Which of the following results in a situation in which the chromosome number is either 2n+1 or 2n-1 ?
answer
aneuploidy
An aneuploid individual has either too many or too few chromosomes, usually as a result of nondisjunction.
question
What results if a fragment of a chromosome breaks off and then reattaches to the original chromosome at the same place but in the reverse direction?
answer
an inversion
The question describes an inversion.
question
What is the source of the extra chromosome 21 in an individual with Down syndrome?
answer
nondisjunction or translocation in either parent
question
What is the probability that a son will be a hemophiliac? Express your answer as a fraction (for example, 1/24), or as a whole number.
answer
1/2
question
If the couple has four sons, what is the probability that all four will be born with hemophilia? Express your answer as a fraction (for example, 1/24), or as a whole number.
answer
1/16
question
Sex determination in animals
answer
The mechanism of sex determination varies with different animal species.
There are various chromosomal systems for sex determination found in animals.
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