Some practice genetics problems ANSWER KEY
1. How many different combinations of maternal and paternal chromosomes can be packaged in gametes made
by an organism with a diploid number of 8?
A. 2
B. 4
C. 8
D. 16
E. 32
2. An organism with the genotype of AaXx can produce which combination of gametes if the two genes A &
X are unlinked.
A. Aa, Xx
B. AX, Ax, aX, ax
C. AaXx
D. AX or ax
E. A, a, X, x
3. What are the possible genotypes of a female child from the union of a woman who is heterozygous for
hemophilia and a man who has normal blood clotting characteristics?
A. XHXH or XHXh
B. XHXh
C. XHYH
D. Hh
4. A recessive gene for color blindness is located on the X chromosome in humans. Assume that a woman with
normal vision (but her father is color-blind) marries a color blind male. What are the chances that this
couple’s first son will be color blind?
A. 1/2
B. 0
C. 1/4
D. 1
E. ¾
5. One form of hemophilia is caused by a sex-linked recessive gene. Assume that a man with the disease
marries a woman who is phenotypically normal but whose father had the disease. What is the probability
that the couple’s first son will have the disease?
A. 1/16
B. 1/2
C. 1/8
D. 3/4
E. ¼
6. Which of the following represents the possible genotype(s) resulting from a cross between an individual
homozygous for black hair(BB) and an individual homozygous for blond hair(bb)?
A. BB and Bb
B. BB, Bb, and bb
C. BB only
D. Bb only
.
The following map consists of four genes on a chromosome.
For the genetic map above, between which two genes would you expect the highest frequency of
recombination?
A. A and W
B. W and E
C. A and G
D. A and E
8. Determine the sequence of genes along a chromosome based on the following recombination frequencies:
A-B, 8 map units; A-C, 28 map units; A-D, 25 map units; B-C, 20 map units; B-D, 33 map units; D-C, 53
map units (HINT: It may be helpful to sketch a diagram similar to the one in question 9 before determining
a solution)
Solution: D-A-B-C