Chapter 15 Questions Flashcards
The chromosome theory of inheritance states that _____.
- genes occupy specific positions on chromosomes
- homologous chromosomes segregate from each other during meiosis
- chromosomes assort independently during meiosis
Why did Morgan choose Drosophila for his genetics experiments?
- A single mating can produce many offspring.
- Drosophila chromosomes can be easily distinguishable under a light microscope.
Wild type refers to _____.
the most common phenotype thought to be found in the natural population
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.
What is the probability that a male will inherit an X-linked recessive allele from his father?
0%
In an X-linked, or sex-linked, trait, it is the contribution of _____ that determines whether a son will display the trait
the mother
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?
Half of their sons will have the recessive trait.
-All the sons will receive Y chromosomes from their father. The X must come from the heterozygous mother; therefore, each son has a 50% chance of inheriting the recessive allele.
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?
50%
-The female werewolf must be heterozygous, because her father has round ears. Each of her sons has a 50% chance of inheriting the round allele.
A woman is red-green color-blind. What can we conclude, if anything, about her father?
He is red-green color-blind.
-A normal male cannot father a red-green color-blind daughter.
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?
0%
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.
-Moreover, males carrying the allele have less of an opportunity to have offspring.
Hemophilia is a sex-linked disorder. The daughter of a father with hemophilia and a carrier mother has a _____ probability of having hemophilia.
50%
-The mother is XHXh, and the father is XhY. The daughter must receive Xh from the father and has a 50% chance of receiving Xh from the mother.
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?
Either her mother was a carrier or her father had hemophilia.
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.
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 _____.
X chromosome inactivation
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?
She is XXX.
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.
Which of the following best describes the function of the XIST gene in X chromosome inactivation?
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.
If two genes are linked, _____.
they are on the same chromosome
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?
The genes for hair color and eye color are linked.
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.
black-bodied, normal-winged … black-bodied, vestigial-winged
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 _____.
unlinked
-Two genes on different chromosomes assort independently.
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
-C must lie between A and B (5 +14 = 19). Similarly, D must be beyond B to be 21 units from A and 2 units from B.
In question 18, the observed distribution of offspring was as follows: black-red 1,070; black-white 177; green-red 180; green-white 1,072. Based on these data, what is the recombination frequency?
approximately 14%
-Recombination frequency = (number of recombinants)/(total offspring) × 100.
A linkage map _____.
orders genes on a chromosome based on recombination frequencies
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
- random fertilization increasing the number of possible allele combinations in an individual
need to add the concepts after 15.3.
this only has concepts 15.1,15.2, and 15.3
What can we observe in order to visualize Mendel’s Law of Segregation?
homologous chromosomes separating during meiosis I
-Homologous chromosomes each carry an allele for every gene. Those alleles may be the same or different, but they are segregated during meiosis I and distributed to each gamete.
What name is given to the most common phenotype in a natural population?
wild type
-The most common phenotype is the wild type.
