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Genetic Crosses
Level I – Answers
1.
A. What is the ratio of offspring with rough coat to
smooth coat? Explain.
r
Rough to smooth is 1:1, because two of four
offspring will have rough coat (Rr) and two
will have smooth coat (rr). Rough coat is
dominant over smooth.
B. What is the probability of getting an offspring
with a smooth coat? Explain.
50% because 2 out of four equals 50%.
2. A.
r
R
Rr
Rr
r
rr
rr
What is the genotype of the offspring?
RW
W
W
R
RW
RW
R
RW
RW
B. What is the probability of getting a red flower
from this cross?
0%
because none are RR
C. What is the probability of getting a white flower
from this cross?
0% because none are WW
D. What is the phenotype of the offspring?
Pink all are RW. This is an example of incomplete dominance.
3. A.
What are the possible blood types of the offspring?
AB, AO, BO, OO
B. What is the probability of the offspring having
type A blood? Explain.
25% because one out of four has AO blood
and A is dominant.
C. What is the probability of the offspring having
type AB blood? Explain.
25% because one out of four has AB blood.
A
B
O
O
AB
BO
AO
OO
D. What is the probability of the offspring having
type B blood? Explain.
25% because one out of four has BO blood and B is dominant.
E. What is the probability of the offspring having
type O blood? Explain.
25% because one out of four has OO blood and O is recessive.
4.
A. What percentage of daughters is normal?
50% because one out of two daughters are XX
B. What percentage of daughters has hemophilia?
0% because none are XhXh
C. What percentage of daughters are carriers?
50% because one out of two areXhX. This is
A carrier because Xh is recessive.
D. What percentage of sons has hemophilia?
50% because one out of two are XhY
E. What percentage of sons is normal?
50% because one out of two are XY
XH
h
X
XH
Y
XH XH
XH Y
XHXh
XhY
Genetic Crosses
Level II – Answers
1.
R
r
r
Rr
rr
r
Rr
rr
R = red
r = yellow
50% are red because two out of four are Rr and R is dominant over r.
50% are yellow because two out of four are rr and r is recessive.
2.
RR = red cattle
RW= roan cattle
WW = white cattle
R
R
R
RR
RR
W
RW
RW
0% is white because none of the offspring are WW.
50% are red because two out of four are RR.
50% are roan because two out of four are RW which shows incomplete dominance.
3.
A
B
O
AO
BO
O
AO
BO
0% will have type AB blood because none are AB.
0% will have type O blood because none are OO.
50% will have type A blood because two out of four are AO and A is dominant over O.
50% will have type B blood because two out of four have BO. And B is dominant over
O.
Xc
4.
Y
XC
XCXc
XC Y
Xc
XcXc
XcY
50% of the daughters will be colorblind because one out of two is XcXc.
50% of the daughters will be carriers for colorblindness because one out of two is XcX.
0% of the daughters will be normal because none are XX.
50% of the sons will be colorblind because one out of two is XcY and the recessive gene
is not part of the Y chromosome, so it is expressed here.
50% of the sons will be normal because one out of two isXY.
Genetic Crosses
Level III – Answers
1.
T
t
T
t
TT
Tt
Tt
Tt
When two hybrids are crossed the recessive trait can be produced 25% of the time. The
dominant trait will be produced 75% of the time (25% pure TT, 50% hybrid).
2.
A
A
O
AO
AO
O
AO
AO
When the father is homozygous for type A blood (AA) and the mother is homozygous
for type O blood (OO), this represents a cross between a homozygous dominant and a
homozygous recessive. In this case all of the offspring will be heterozygous (AO).
Therefore all the offspring will have type A blood.
3. Both parents have black hair (heterozygous) and brown eyes (heterozygous).
Genotype of father BbEe
Genotype of mother BbEe
Complete the Punnett Square
B
B
b
BB
b
E
Bb
E
Bb
bb
e
One out of sixteen
e
EE
Ee
Ee
ee
1/ 16 or 6.25% will have blonde hair and blue eyes.
The phenotype ratio of individuals with brown hair and brown eyes, brown hair and
blue eyes, blonde hair and brown eyes, and blonde hair and blue eyes is:
9:3:3:1
because 9 out of 16 will have brown hair and brown eyes, 3 out of 16 will have brown
hair and blue eyes, 3 out of 16 will have blonde hair and brown eyes, and 1 out of 16
will have blonde hair and blue eyes.