Genetics Problems 3
1. A woman is heterozygous for both type A blood and for Rh factor. If she had a baby with a man
who has O+ (0 positive) blood and is fully homozygous for these traits, what are the possible
blood types of their children?
The Punnett Square
? The cross: ?
X
Blood types possible in children?
(Put a in empty squares if there are fewer possibilities than blanks.)
Why can you get the correct results with the Punnett square shown (with only one row for the
man, but four for the woman)? (Explain.)
2. Hemophilia is a recessive, sex-linked trait. If a woman who is a carrier for hemophilia marries a
normal man, what are the odds their sons will have hemophilia? What are the odds that their
daughters will have hemophilia? What are the odds their daughters will be carriers of the
hemophilia gene? Use the following genes for this problem: XN = X gene for normal blood
clotting ; Xn = X with hemophilia gene; Y = Y chromosome.
The Punnett Square
?
? The cross: ?
X
?
Odds of sons with hemophilia?
out of
Odds of daughters with hemophilia?
Odds of carrier daughters?
out of
out of
Genetics Problems 3
In shorthorn cattle the gene for red coat (R) is not dominant over that for white coat (Rn Cattle
heterozygous for this gene are roan colored (In other words, inheritance of these traits is governed by
incomplete dominance). The gene that codes for the polled condition of the horns (P) is clearly
dominant over the gene that codes for long horns (p). (In other words, inheritance of these traits is
governed by simple dominance.)
a. Write out the genotype for a cow that is heterozygous for both traits. What would this
cow look like with respect to these traits?
Genotype
Phenotype
b. Do a Punnett square which illustrates the potential offspring for a cross between the
cow above and a bull with the same genotype.
?
?
c. On average what percentage of the calves of numerous similar crossings would have
each of the following sets of characteristics?
1) A red coat and polled horns.
2) A white coat and long horns.
3) A roan coat and polled horns.

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