Genetics Homework - Bio 105 Fall 2011
Answers
Always provide a key for your letters
1. A homozygous yellow pea plant is crossed with a homozygous green pea plant, Yellow is the
dominant trait for pea plants:
A) Key:
Y=yellow
y=green
_YY_____
C) Genotype of green pea plant: __yy_____
B) Genotype of yellow pea plant:
D) Draw the Punnett square of the cross
Y
Y
y
Yy
Yy
y
Yy
Yy
E) What percentage of the offspring will be yellow? ____100%_______
2. In people, freckles are dominant over not having freckles, it is an autosomal trait. Two people who
are both heterozygous for freckles get married.
A) Key:
F = freckles
f = no freckles
___Ff_____
C) Genotype of the wife: ____Ff____
B) Genotype of the husband:
D) Draw a Punnett square of the cross between the two people.
F
f
F
FF
Ff
f
Ff
ff
E) What is the probability that they will produce an offspring that has freckles? 75% or 3/4
3. Brown eyes are dominant over blue eyes, it is an autosomal trait. A brown-eyed couple gets married,
the husband is homozygous for brown eyes and the wife is heterozygous.
A) Key:
B = brown
b = blue
_BB_______
Genotype of the wife: _Bb_______
B) Genotype of the husband:
C) Draw a Punnett square of the cross between the two people.
B
BB
B
BB
BB
b
Bb
Bb
D) What is the probability that the couple will have a child with blue eyes? 100%
4. Cystic fibrosis has been found to be inherited through a recessive autosomal allele. A man with
cystic fibrosis marries a woman who does not have cystic fibrosis, but her mother had the disease.
A) Key:
C= normal
c = cystic fibrosis
B) Genotype of the wife: Cc
C) Genotype of the husband:
___cc___
D) Draw a Punnett square of the cross between the two people.
C
c
c
Cc
cc
c
Cc
cc
B) What is the probability that their next child would be expected to have the disease? 50% or 2/4
5. What are the possible genotypes of the children if the mother has Type B blood and the father has
type O blood? (Draw a Punnett square to verify your answer, you may need more than one Punnett
square.)
___ BB or Bo ____
B) Genotype of the father: ____ oo ____
A) Genotype (or genotypes) of the mother:
C) Draw a Punnett square(s) of the cross between the two people.
B
B
o
Bo
Bo
o
Bo
Bo
B
o
o
Bo
oo
o
Bo
oo
6. A mother has blood type O, her child is type O. She claims a man of type AB is the father. Could he
be? __no_______________ Draw a Punnett Square of the cross.
A
B
o
Ao
Bo
o
Ao
Bo
Could a man of type A, type B, or type O be the father? __ yes if the are Ao or Bo or oo____________.
Draw the punnett squares of the crosses
B
o
o
Bo
oo
o
Bo
oo
o
o
o
oo
oo
o
oo
oo
B
o
o
Bo
oo
o
Bo
oo
7. Sickle cell anemia is an autosomal recessive disease. A couple comes to you for advice. Both of
their fathers had sickle cell anemia but neither the husband nor the wife have the disease.
A) Key:
S=normal
s=sickle cell anemia
_ _____
B) Genotype of the couple: Ss
C) Draw a Punnett square of the cross between the two people.
S
s
S
SS
Ss
s
Ss
ss
D) What is the probability that their child will have the disease ___25% or 1/4____________
E) What is the probability that their child will be a carrier for the disease. __50% or 2/4_______
8. Red-green color blindness is due to a sex-linked recessive allele on the X chromosome.
Two normal visioned parents produce a color-blind son.
A) Key:
XB = normal
Xb = color blind
___X X _____
C) Genotype of the husband: __ X Y______
B
B) Genotype of the wife:
b
B
D) Draw a Punnett square of the cross between the two people.
XB
Y
XB
XBXB
XBY
Xb
XB Xb
XbY
E) What is the probability that their next child will be color blind? __25%________
9. Huntingtons disease is a dominant autosomal disease. What is the probability that a couple will have
a child that will develop huntingtons if the husband is heterozygous for Huntingtons and the wife is
homozygous recessive.
A) Key:
H=huntingtons
h=normal
__hh____
C) Genotype of the husband: _Hh_______
B) Genotype of the wife:
D) Draw a Punnett square of the cross between the two people.
H
h
h
Hh
hh
h
Hh
hh
E) What is the probability that a couple will have a child that will develop huntingtons? 50% or 2/4