Ch 12: Chromosomal Basis of Inheritance Flashcards
During meiosis, homologous chromosomes sometimes “stick together” and do not separate properly. This phenomenon is known as __________.
nondisjunction
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.
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.
In which of the following structures would you expect to find a Barr body?
a liver cell of a woman
In an X-linked, or sex-linked, trait, it is the contribution of __________ that determines whether a son will display the trait.
the mother
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.
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
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.
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
A wild type is ___________.
the phenotype found most commonly in nature
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 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%
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
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
