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35 Cards in this Set
- Front
- Back
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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?
The gene involved is on the Y chromosome. Other male-specific factors influence eye color in flies. The gene involved is on an autosome, but only in males. Other female-specific factors influence eye color in flies. The gene involved is on the X chromosome. |
The gene involved is on the X chromosome
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Sturtevant provided genetic evidence for the existence of four pairs of chromosomes in Drosophila in which of these ways?
Drosophila genes have, on average, four different alleles. Drosophila genes cluster into four distinct groups of linked genes. The overall number of genes in Drosophila is a multiple of four. There are four major functional classes of genes in Drosophila. The entire Drosophila genome has approximately 400 map units. |
Drosphila genes cluster into 4 distinct groups of genes
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A woman is found to have 47 chromosomes, including three X chromosomes. Which of the following describes her expected phenotype?
healthy female of slightly above-average height sterile female excessive emotional instability enlarged genital structures masculine characteristics such as facial hair |
Healthy Female of slightly above average height
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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?
50% 75% 100% 0% 25% |
100%
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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?
3:1 male to female 4:3 male to female 1:1 male to female 1:2 male to female 2:1 male to female |
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?
a person with an extra X chromosome Turner syndrome, 45, X a person with one normal and one shortened (deleted) X translocation of SRY to an autosome of a 46, XX individual Down syndrome, 46, XX |
translocation of SRY to an autosome of a 46, XX individual
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In humans, clear gender differentiation occurs, not at fertilization, but after the second month of gestation. What is the first event of this differentiation?
activation of SRY in male embryos and masculinization of the gonads activation of SRY in females and feminization of the gonads anatomical differentiation of a penis in male embryos formation of testosterone in male embryos formation of estrogens in female embryos |
activation of SRY in male embryos and masculinization of the gonads
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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 20s. How likely is it for a woman to have this condition?
One-half of the daughters of an affected man would have this condition. Women can never have this condition. One-fourth of the daughters of an affected father and a carrier mother could have this condition. Only if a woman is XXX could she have this condition. Very rarely: it is rare that an affected male would mate with a carrier female. |
Very rarely: it is rare that an affected male would mate with a carrier female.
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All female mammals have one active X chromosome per cell instead of two. What causes this?
inactivation of the XIST gene on the X chromosome derived from the male parent crossing over between the XIST gene on one X chromosome and a related gene on an autosome attachment of methyl (CH3) groups to the X chromosome that will remain active activation of the BARR gene on one X chromosome, which then becomes inactive activation of the XIST gene on the X chromosome that will become the Barr body |
activation of the XIST gene on the X chromosome that will become the Barr body
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Part A
Refer to the following information to answer the question below. 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? none three out of four half all one out of four |
none
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Refer to the following information to answer the question below.
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? 50% 75% 0% 25% 100% |
100%
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Part A
Which of the following statements is true of linkage? All of the traits that Mendel studied–seed color, pod shape, flower color, and others–are due to genes linked on the same chromosome. Linked genes are found on different chromosomes. Crossing over occurs during prophase II of meiosis. The closer two genes are on a chromosome, the lower the probability that a crossover will occur between them. The observed frequency of recombination of two genes that are far apart from each other has a maximum value of 100%. |
The closer 2 genes are on a chromosome, the lower the probability that a crossover will occur between them
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How would one explain a testcross involving F1 dihybrid flies in which more parental-type offspring than recombinant-type offspring are produced?
Both of the characters are controlled by more than one gene. The two genes are linked but on different chromosomes. The testcross was improperly performed. Recombination did not occur in the cell during meiosis. The two genes are closely linked on the same chromosome. |
The two genes are closely linked on the same chromosome.
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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?
The three genes are showing independent assortment. The three genes are linked. Gene A is linked but genes B and C are not. Gene A is assorting independently of genes B and C, which are linked. Gene A is located 14.4 map units from genes B and C. |
Gene A is assorting independently of genes B and C, which are linked.
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What is one map unit equivalent to?
the recombination frequency between two genes assorting independently 1% frequency of recombination between two genes the distance between a pair of homologous chromosomes 1 nanometer of distance between two genes the physical distance between two linked genes |
1% frequency of recombination between two genes
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Which statement about recombination between linked genes is correct?
Recombination must occur or genes will not assort independently. Without recombination there would be an insufficient number of gametes. The forces on the cell during meiosis II always result in recombination. Recombination is a requirement for independent assortment. New allele combinations may result in differential reproductive success. |
New allele combinations may result in differential reproductive success.
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Map units on a linkage map cannot be relied upon to calculate physical distances on a chromosome for which of the following reasons?
Linkage map distances are identical between males and females. The relationship between recombination frequency and map units is different in every individual. The frequency of crossing over varies along the length of the chromosome. The gene order on the chromosomes is slightly different in every individual. Physical distances between genes change during the course of the cell cycle. |
The frequency of crossing over varies along the length of the chromosome.
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Use the following information to answer the questions below.
A plantlike organism on the planet Pandora can have three recessive genetic traits: bluish leaves, due to an allele (a) of gene A; a feathered stem, due to an allele (b) of gene B; and hollow roots due to an allele (c) of gene C. The three genes are linked and recombine as follows: 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): Phenotypes Leaves Stems Roots Number 1 a + + 14 2 a + c 0 3 a b + 32 4 a b c 440 5 + b + 0 6 + b c 16 7 + + c 28 8 + + + 470 Total 1,000 If recombination frequency is equal to distance in map units, what is the approximate distance between genes A and B? 30 map units 15 map units 1.5 map units 3 map units 6 map units |
3 Map units
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In a series of mapping experiments, the recombination frequencies for four different linked genes of Drosophila were determined as shown in the figure. What is the order of these genes on a chromosome map?
vg-b-rb-cn cn-rb-b-vg rb-cn-vg-b b-rb-cn-vg vg-cn-b-rb |
b-rb-cn-vg
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Part A
Use the following information to answer the questions below. A plantlike organism on the planet Pandora can have three recessive genetic traits: bluish leaves, due to an allele (a) of gene A; a feathered stem, due to an allele (b) of gene B; and hollow roots due to an allele (c) of gene C. The three genes are linked and recombine as follows: 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): Phenotypes Leaves Stems Roots Number 1 a + + 14 2 a + c 0 3 a b + 32 4 a b c 440 5 + b + 0 6 + b c 16 7 + + c 28 8 + + + 470 Total 1,000 What is the greatest benefit of having used a testcross for this experiment? The homozygous recessive parents are obvious to the naked eye. The homozygous parents are the only ones whose crossovers make a difference. Progeny can be scored by their phenotypes alone. All of the progeny will be heterozygous. The homozygous recessive parents will be unable to cross over. |
Progeny can be scored by their phenotypes alone.
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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?
There will be three extra gametes. 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. All the gametes descended from cell X will be diploid. Half of the gametes descended from cell X will be n + 1, and half will be n - 1. Two of the four gametes descended from cell X will be haploid, and two will be diploid. |
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.
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A nonreciprocal crossover causes which of the following products?
nondisjunction deletion and duplication duplication and nondisjunction duplication only deletion only |
deletion and duplication
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Of the following human aneuploidies, which is the one that generally has the most severe impact on the health of the individual?
47, +21 47, XXY 45, X 47, XYY 47, XXX |
47, +21
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A phenotypically normal prospective couple seeks genetic counseling because the man knows that he has a translocation of a portion of his chromosome 4 that has been exchanged with a portion of his chromosome 12. Although he is normal because his translocation is balanced, he and his wife want to know the probability that his sperm will be abnormal. What is your prognosis regarding his sperm?
All will carry the same translocation as the father. 1/2 will be normal and the rest will have the father's translocation. 1/4 will be normal, 1/4 will have the translocation, and 1/2 will have duplications and deletions. His sperm will be sterile and the couple might consider adoption. None will carry the translocation since abnormal sperm will die. |
1/4 will be normal, 1/4 will have the translocation, and 1/2 will have duplications and deletions.
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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?
death of the cancer cells in the tumor sensitivity of the immune system a decrease in mitotic frequency an increase in nondisjunction expression of inappropriate gene products |
expression of inappropriate gene products
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An inversion in a human chromosome often results in no demonstrable phenotypic effect in the individual. What else may occur?
The individual is more likely to get cancer. There is an increased frequency of mutation. Some abnormal gametes may be formed. There may be deletions later in life. All inverted chromosomes are deleted. |
Some abnormal gametes may be formed.
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What is a syndrome?
a group of traits, all of which must be present if an aneuploidy is to be diagnosed a characteristic that only appears in conjunction with one specific aneuploidy a characteristic trait usually given the discoverer's name a characteristic facial appearance a group of traits typically found in conjunction with a particular chromosomal aberration or gene mutation |
a group of traits typically found in conjunction with a particular chromosomal aberration or gene mutation
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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?
The mother had a chromosomal duplication. One member of the couple underwent nondisjunction in somatic cell production. One member of the couple carried a translocation. The woman inherited this tendency from her parents. One member of the couple underwent nondisjunction in gamete production. |
One member of the couple underwent nondisjunction in gamete production.
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Which of the following is known as a Philadelphia chromosome?
a human chromosome 22 that has had a specific translocation an animal chromosome found primarily in the mid-Atlantic area of the United States a chromosome found not in the nucleus but in mitochondria a human chromosome 9 that is found only in one type of cancer an imprinted chromosome that always comes from the mother |
a human chromosome 22 that has had a specific translocation
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At what point in cell division is a chromosome lost so that, after fertilization with a normal gamete, the result is an embryo with 45, X?
I. an error in anaphase I II. an error in anaphase II III. an error of the first postfertilization mitosis IV. an error in pairing III or IV only II or IV only I or II only I, II, or III only I, II, III, or IV |
I, II, III, or IV
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Correns described that the inheritance of variegated color on the leaves of certain plants was determined by the maternal parent only. What phenomenon does this describe?
sex-linkage mitochondrial inheritance genomic imprinting infectious inheritance chloroplast inheritance |
chloroplast inheritance
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Genomic imprinting is generally due to the addition of methyl (–CH3) groups to C nucleotides in order 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?
Methylation must be reversible in ovarian and testicular cells. Methylation of this kind must occur more in males than in females. Genes required for early development stages must not be imprinted. Methylation of C is permanent in a gene. The imprints are transmitted only to gamete-producing cells. |
Methylation must be reversible in ovarian and testicular cells.
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Mitochondrial DNA is primarily involved in coding for proteins needed for electron transport. Therefore, in which body systems would you expect most mitochondrial gene mutations to be exhibited?
the nervous and muscular systems the circulation system the excretory and respiratory systems the skin and senses the immune system and the blood |
the nervous and muscular systems
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Suppose that a gene on human chromosome 18 can be imprinted in a given pattern in a female parent but not in a male parent. A couple in whom each maternal meiosis is followed by imprinting of this gene have children. What can we expect as a likely outcome?
Each of the children will imprint a different chromosome. All sons but no daughters will bear their mother's imprinting pattern. All sons and daughters will have a 50% chance of receiving the mother's imprinting pattern. All the children will bear their mother's imprinting pattern but only daughters will then pass it down. All daughters but no sons will bear their mother's imprinting pattern. |
All the children will bear their mother's imprinting pattern but only daughters will then pass it down.
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The pedigree in the figure shows the transmission of a trait in a particular family. Based on this pattern of transmission, the trait is most likely
mitochondrial. autosomal recessive. sex-linked recessive. autosomal dominant. sex-linked dominant. |
Mitochondrial
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