Chapter 12 Flashcards
The human body contains __ chromosomes that come in __ homologous pairs
46
23
Two examples of diseases inherited on the x chromsome
color blindness
hemophilia
Is baldness caused by a recessive or dominant allele?
recessive
Sex-linked traits are said to _____ a generation
skip
Meiosis is responsible for producing _____ ________ cells from one original cell
four
haploid
failure of chromosomes to separate from each other during either round of meiosis; can occur in either meiosis or mitosis in either sex
Nondisjunction
Nondisjunction is responsible for syndromes such as
turner syndrome
down syndrome
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
A linkage map __________.
orders genes on a chromosome based on recombination frequencies
A 1:1:1:1 ratio of offspring from a dihybrid testcross indicates that ___________.
the genes are not linked or are more than 50 map units apart
The chromosome theory of inheritance states that __________.
genes occupy specific positions on chromosomes, homologous chromosomes segregate from each other during meiosis, and chromosomes assort independently during meiosis
A wild type is ___________.
the phenotype found most commonly in nature
When a person has Down syndrome, he or she has an extra chromosome 21. Therefore, Down syndrome is a kind of __________ and results from __________.
aneuploidy; nondisjunction of chromosome 21 during meiosis I
The recombination frequency between two gene loci __________.
increases as the distance between the two loci increases
Why did Thomas Hunt Morgan choose Drosophila for his genetics experiments?
A single mating can produce many offspring, and Drosophila chromosomes can be easily distinguishable under a light microscope.
In which of the following structures would you expect to find a Barr body?
a liver cell of a woman
Which of the following is the only known viable human monosomy?
XO
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
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 __________.
inversion
During meiosis, homologous chromosomes sometimes “stick together” and do not separate properly. This phenomenon is known as __________.
nondisjunction
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.
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 __________.
translocation occurred
A woman is red-green color-blind. What can we conclude, if anything, about her father?
Her father is red-green color-blind.
In an X-linked, or sex-linked, trait, it is the contribution of __________ that determines whether a son will display the trait.
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.
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 molecules that bind to that same chromosome and effectively cover it up.
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.
Individuals with an extra X chromosome __________.
may have subnormal intelligence or be at risk for learning disabilities
In werewolves, 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%
Hemophilia is a sex-linked disorder. The daughter of a father with hemophilia and a carrier mother has a __________ probability of having hemophilia.
50%
