GENETICS PROBLEMS
1. A man with a widow’s peak (WW) marries a woman with a continuous hairline (ww). What kind
of hairline will their children have?
a. Genotype of gametes produced: male = ___W___________, female = ____w_________
b. Show the cross here:
w
w
W
Ww
Ww
W
Ww
Ww
c. Children’s: genotype = _____all_Ww_________, phenotype = _all widow’s peak_____
2. Suppose one of the children from the above problem (Ww) marries someone who is also
heterozygous (Ww). What type of hairline will their children have?
a. Genotype of gametes produced: male = ___W or w______, female = ___W or w______
b. Show the cross here:
W
w
W
WW
Ww
w
Ww
ww
3. Children’s: genotype = _WW, Ww, ww_______, phenotype = _widow’s peak & continuous__
4. A woman is homozygous dominant for short fingers (SS). She marries a man who is
heterozygous for short fingers (Ss).
a. Genotype of gametes produced: male = ___S__________, female = ___S or s_______
b. Show the cross here:
S
s
S
SS
Ss
S
SS
Ss
c. Will any of their children have long fingers(ss), yes or no? ___no____________
d. Could any of the grandchildren of the above couple potentially have long fingers? Why
or why not? (Hint: It may help to show any possible crosses.)
Yes, if one of the heterozygous children (Ss) marry another heterozygous (Ss) or
homozygous recessive individual (ss), then it would be possible.
5. Jane and John are expecting a baby and know that they are both carriers (i.e. heterozygous) of
cystic fibrosis (Cc). What is the probability that their child will have cystic fibrosis (cc)? What is
the probability that their child will be a carrier of cystic fibrosis?
Chance of child being:
___25%_______ disease free; genotype = __CC_____________
___50%_______ cystic fibrosis carrier; genotype = ____Cc_____
___25%_______ cystic fibrosis; genotype = ______cc_________
6. You have freckles and dimples (FfDd). Your significant other has freckles but no dimples (Ffdd).
What is the chance your child would have both recessive phenotypes: no freckles and no
dimples (ffdd)? (Hint: do a dihybrid cross using the foil method)
a. Genotype of gametes produced: male = _FD, Fd, fD, or fd__, female = __Fd or fd___
b. Show the cross here:
FD
Fd
fD
fd
Fd
FFDd
FFdd
FfDd
Ffdd
fd
FfDd
Ffdd
ffDd
ffdd
Fd
FFDd
FFdd
FfDd
Ffdd
fd
FfDd
Ffdd
ffDd
ffdd
c. % no freckles and no dimples: _____2/16 = 1/8___________
7. All the offspring of a cross between a black-eyed mendelien and an orange-eyed mendelien
have black eyes. What is the expected phenotypic ratio of a cross between two orange-eyed
mendeliens?
Black eyes are dominant (B), orange eyes are recessive (b)
b
b
b
bb
bb
b
bb
bb
1; all orange
8. Hemophilia is a recessive genetic disorder whose disorder allele, which we’ll call a, is located on
the X chromosome. What are the chances that parents with the following genotypes will have a
child with hemophilia?
A
a
A
A
a. XAXA x XaY : 0%
b. XAXa x XaY : 50%
A a
A
c. X X x X Y : 25%
d. XaXa x XAY : 50%
A
X
X
B
X
X
Xa
XAXa
XAXa
Xa
XAXa
XaXa
Y
XAY
XAY
Y
XAY
XaY
C
XA
Xa
D
Xa
Xa
XA
XAXA
XAXa
XA
XAXa
XAXa
Y
XAY
XaY
Y
XaY
XaY
9. If blue flower color (B) is dominant to white flower color (b), what are the genotypes of the
parents in the following genetic cross: blue flower x white flower yields only blue-flowered
offspring?
B
b
b
Bb
bb
b
Bb
bb
10.
B
B
b
Bb
Bb
b
Bb
Bb
Not all blue offspring if blue phenotype parent was heterozygous (Bb)
Mother’s genotype: ___Bb_________ Father’s genotype: ___bb_________
11. The fruit pods of peas can be yellow or green. In one of his experiments, Mendel crossed plants
that were homozygous for the allele for yellow fruit pods with plants that were homozygous for
the allele for green fruit pods. All fruit pods in the F1 generation were green. Which allele is
dominant, the one for yellow or the one for green? Briefly explain why, it may help to show the
crosses for each.
G
G
g
Gg
Gg
g
Gg
Gg
Y
Y
y
Yy
Yy
y
Yy
Yy
Green is dominant because it is the only way that all offspring would be green. If yellow were
dominant, then all offspring would be yellow.
12. Color-blindness is a sex-linked gene carried on the X chromosome. A color-blind man and his
wife, with normal vision, have a color-blind daughter. What is the probability that their newborn
son will also be color blind?
N
n
XnY
x
X
X
Xn
XNXn
XnXn
Y
XNY
XnY
XNXn
50%
Only way to have a colorblind daughter would be if mother is heterozygous. This would give a
50:50 chance of a son being colorblind too.
13. Use this pedigree of to determine the genotypes for the following individuals. The trait is
recessive (rr).
Female
Male
Rr
rr
rr
Rr
Rr
rr
rr
rr
Rr
rr
Rr
Affected
(rr(
Unaffected