Bio - ch 15
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| 5) A woman is found to have 47 chromosomes, including three X chromosomes. Which of the following describes her expected phenotype? | normal female
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| 6) Males are more often affected by sex-linked traits than females because | males are hemizygous for the X chromosome.
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| 7) SRY is best described in which of the following ways? | a gene region present on the Y chromosome that triggers male development
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| 1) 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 X chromosome.
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| 3) Which of the following is the meaning of the chromosome theory of inheritance as expressed in the early 20th century? | Mendelian genes are at specific loci on the chromosome and in turn segregate during meiosis.
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| 4) Thomas Hunt Morgan's choice of Drosophila melanogaster has been proven to be useful even today. Which of the following has/have continued to make it a most useful species? | I and IV only (four pairs of chromosomes, short generation time and large number of offspring)
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| 8) 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? | tortoiseshell females; black males
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| 9) 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? | XCXc and XCY
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| 10) 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? | 100%
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| 11) Calico cats are female because | a male inherits only one of the two X-linked genes controlling hair color.
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| 12) Bird males are ZZ, females are ZW. A recessive lethal allele that causes death of the embryo is sometimes on the Z chromosome in pigeons. What would be the sex ratio in the offspring of a cross between a heterozygous male and a normal female? | 2:1 male to female
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| 14) 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
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| 17) Which of the following statements is true of linkage? | The closer two genes are on a chromosome, the lower the probability that a crossover will occur between them.
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| 18) How would one explain a testcross involving F1 dihybrid flies in which more parental-type |
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| 19) What does a frequency of recombination of 50% indicate? | The two genes are likely to be located on different chromosomes.
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| 20) What is the reason that linked genes are inherited together? | They are located close together on the same chromosome.
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| 3genes at 3loci are being mappedEach has2phenotypes-1 is markedly different from the wild typeThe allele of the 1st gene is inherited with either of the others about 50% of the timeThe unusual alleles of the other2are inherited together 14.4% of the time | The first gene is assorting independently from the other two that are linked.
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| 22) The centimorgan (cM) is a unit named in honor of Thomas Hunt Morgan. To what is it equal? | 1% frequency of recombination between two genes
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| 25) Map units on a linkage map cannot be relied upon to calculate physical distances on a chromosome for which of the following reasons? | The frequency of crossing over varies along the length of the chromosome.
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| 27) If nondisjunction occurs in meiosis II during gametogenesis, what will be the result at the completion of meiosis? | 1/4 of the gametes will be n + 1, 1/4 will be n - 1, and 1/2 will be n.
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| male-pattern baldness is controlled by autosomal gene that occurs in 2 forms. Allele Hn determines nonbaldness, al Hb det bald. In males, allele Hb is dom over Hn. If man & woman both w/ genotype HnHb have son, what is chance he will b bald? | 75%
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| 33) 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? | expression of inappropriate gene products
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| 34) An inversion in a human chromosome often results in no demonstrable phenotypic effect in the individual. What else may occur? | Some abnormal gametes may be formed.
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| 35) What is the source of the extra chromosome 21 in an individual with Down syndrome? | nondisjunction or translocation in either parent
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| 36) Down syndrome has a frequency in the U.S. population of ~1/700 live births. In which of the following groups would you expect this frequency to be significantly higher? | No groups have such higher frequency.
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| 37) 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? | One member of the couple underwent nondisjunction in gamete production.
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| 45) 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.
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| 46) 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? | chloroplast inheritance
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| 53) The pedigree in Figure 15.3 shows the transmission of a trait in a particular family. Based on this pattern of transmission, the trait is most likely | mitochondrial.
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| 17) Which of the following statements is true of linkage? | The closer two genes are on a chromosome, the lower the probability that a crossover will occur between them.
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| 24) Why does recombination between linked genes continue to occur? | New allele combinations are acted upon by natural selection.
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jonnymac07