genetics2 - nishi

[ArchivalUser]

1. A cloned DNA fragment, when used as a probe, reveals a restriction fragment length polymorphism
(RFLP) in the region adjacent to the centromere of chromosome 21. Four haplotypes exist: A, B,
C, and D. An AB woman and a CD man have a child with trisomy 21 who is ACC. Nondisjunction
occurred in

A. the child during the first mitotic division

B. the father during meiosis I

C. the father during meiosis II

D. the mother during meiosis I

E. the mother during meiosis II



2. Examination of a karyotype taken from a metaphase preparation reveals the presence of an extra
chromosome. Which of the following is the most common mechanism of producing this phenomenon?

A. Balanced translocation

B. Chromosomal breakage

C. Fertilization by two sperm

D. Nondisjunction

E. Unbalanced translocation


3. A 13-year-old boy is brought to a rural clinic because of poor school performance. His parents
state that he did not begin talking until after three years of age, and still does not use
language as effectively as his sister, who is 6-years-old. A careful family history reveals that
a maternal grandfather was mildly retarded. The mother has two sisters, both of whom are
apparently normal, but the mother admits that she did not do well in school, and dropped out at
the age of 16. Physical examination of the child reveals large ears, a long, narrow face, and
large testes. Which of the following genetic mechanisms most likely accounts for the observed
findings in the son?

A. Expanded trinucleotide repeat

B. Genomic imprinting

C. Robertsonian translocation

D. Trisomy 13

E. Trisomy 18


4. In a certain population, the frequency of color-blind males is 1 in 100. Assuming that the
population is in Hardy-Weinberg equilibrium at this locus, the frequency of color-blind females
is approximately

A. 0.0001

B. 0.0005

C. 0.01

D. 0.02

E. 0.025

[ArchivalUser]

1.C
2.D
3.A
4.C

[ArchivalUser]

1-C
2-E?D?
3-A
4-?

[ArchivalUser]

hey nishi,steady..or neone...is it ok if i do only q bank 2005 coz the posted 2006 q bank has ans given diffrenetly an not in order as qs...is thr a major diff in the 2 q banks? pls lemme know

[ArchivalUser]

hey docman,
i did qbank from 2005 and q book also....i dont think there is much diff....but it's ok to do 2005, since it is still very uptodated....i even compared with 2004..even that is pretty good...

[ArchivalUser]

1. The correct answer is C. The RFLP detects a region near the centromere of chromosome 21. The
region around the centromere exhibits a phenomenon called crossover suppression. Since genetic
exchange cannot happen in this area, the probe is a reliable marker for the individual
chromosomes. During meiosis II, sister chromatids, which are two identical copies of the same
chromosome, should separate. If a nondisjunction event occurs in this division, two copies of
the same chromosome are passed to the progeny. In this case, both parents are heterozygous for
the probe. The child received an A from the mother and two Cs from the father, leading us to
conclude that the problem occurred in the father during meiosis II.


2. The correct answer is D. Nondisjunction can occur in both meiosis and mitosis, and refers to a
failure of paired chromosomes to separate and go to different daughter cells. When this happens,
one daughter cell gets an extra chromosome and the other daughter cell is "short" one
chromosome.


3. AAAAAAAAAAAA

4.
The correct answer is A. Color blindness is an X-linked recessive trait. A male is hemizygous
for the X chromosome, and thus has only one copy of each trait. The frequency of an X-linked
recessive in males is thus equal to the frequency of the allele in the population. From this, we
know that q = 0.01 and p = 0.99. A female has two copies of each gene on the X chromosome, so
the equation for Hardy-Weinberg equilibrium is the same as for the autosomal traits. In this
case, a homozygous recessive female would occur at a frequency of q2 or 0.0001.