BIOLOGY FINAL EXAM REVIEW CH.12 QUESTIONS
Q: 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?
A: 0%
Q: What is the probability that a male will inherit an X-linked recessive allele from his father?
A: 0%
Q: Hemophilia is a sex-linked disorder. The daughter of a father with hemophilia and a carrier mother has a __________ probability of having hemophilia.
A: 50%.
Q: In werewolves (hypothetically), pointy ears (P) are dominant over round ears (p). The gene 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?
A: 50%.
Q: Why did Morgan choose Drosophila for his genetics experiments?
A: A single mating can produce many offspring. & Drosophila chromosomes can be easily distinguishable under a light microscope.
Q: Which of the following results of Thomas Hunt Morgan's experiments with white-eyed mutant flies was unexpected in light of Mendelian genetics?
A: Among the F2 progeny, only males had white eyes. All of the females had red eyes
Q: Cells that have a number of chromosomes different from the normal number for their species are known as __________.
A: Aneuploidy
Q: 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?
A: Aneuploidy
Q: Queen Victoria was a carrier of a recessive sex-linked allele for hemophilia. Which of the following possibilities could explain the presence of the hemophilia allele in her genotype?
A: Either her mother was a carrier or her father had hemophilia.
Q: Why are individuals with an extra chromosome 21, which causes Down syndrome, more numerous than individuals with an extra chromosome 3 or chromosome 16?
A: Extra copies of the other chromosomes are probably fatal to the developing embryo.
Q: A woman is red-green color-blind. What can we conclude, if anything, about her father?
A: He is red-green color-blind.
Q: 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 __________.
A: translocation occurred
Q: 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?
A: Matings of soft ray males and bony ray females give different results from the matings of bony ray males and soft ray females.
Q: __________ is usually less severe than __________, and __________ species have been observed in plants, fish, amphibians, and even mammals.
A: Polyploidy ... aneuploidy ... polyploid
Q: With a microscope, you examine some somatic cells from a woman and notice that each nucleus has two Barr bodies. What can you infer about the sex chromosomes in this individual?
A: She is XXX.
Q: X-linked genes differ from Y-linked genes in which of the following ways?
A: 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.
Q: Which of the following best describes the function of the XIST gene in X chromosome inactivation?
A: The XIST gene on the X chromosome to be inactivated is expressed to produce multiple RNA transcripts that bind to that chromosome and effectively cover it up, thereby generating a Barr body.
Q: 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. Which of these explanations accounts for this ratio?
A: The genes for hair color and eye color are linked.
Q: In an X-linked, or sex-linked, trait, it is the contribution of __________ that determines whether a son will display the trait.
A: The mother
Q: If a mother is heterozygous for a recessive sex-linked trait and her husband has the dominant allele, which one of the following is true about the probabilities for their children?
A: Their sons will have a 50% chance of inheriting the recessive allele
Q: 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?
A: To express an X-linked recessive allele, a female must have two copies of the allele.
Q: Which of the following is the only known viable human monosomy?
A: Turner's syndrome, or XO, is the only viable human monosomy.
Q: 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 __________.
A: Unlinked.
Q: 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 __________.
A: X chromosome inactivation
Q: When a person has Down syndrome, he or she has an extra chromosome 21. Therefore, Down syndrome is a kind of __________ and results from __________.
A: aneuploidy ... nondisjunction of chromosome 21 during meiosis I
Q: 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.
A: black-bodied, normal-winged ... black-bodied, vestigial-winged
Q: Which type of chromosomal alteration is responsible for the cri du chat syndrome?
A: deletion
Q: The chromosome theory of inheritance states that __________.
A: genes occupy specific positions on chromosomes homologous chromosomes segregate from each other during meiosis chromosomes undergo independent assortment during meiosis
Q: The recombination frequency between two gene loci is __________.
A: greater as the distance between the two loci increases
Q: Which of the following would result in genetic variation by way of new combinations of alleles?
A: independent alignment of homologous chromosomes during meiosis I the exchange of alleles between homologous chromosomes during meiosis I random fertilization increasing the number of possible allele combinations in an individual
Q: 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 __________.
A: inversion
Q: Because the frequency of crossing over is not uniform along the length of a chromosome, __________.
A: map units do not necessarily correlate to physical distances along the chromosome
Q: Individuals with an extra X chromosome __________.
A: may have subnormal intelligence or be at risk for learning disabilities
Q: During meiosis, homologous chromosomes sometimes "stick together" and do not separate properly. This phenomenon is known as __________.
A: nondisjunction
Q: A linkage map __________.
A: orders genes on a chromosome based on recombination frequencies
Q: As an expecting mother of 42 years of age, you are saddened to learn that the results of a prenatal test came back positive for trisomy 21. Although you are distraught by your circumstances, you are somewhat relieved to find out that the Prenatally and Postnatally Diagnosed Conditions Awareness Act was enacted to __________.
A: 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
Q: "Wild type" refers to __________.
A: the most common phenotype thought to be found in the natural population