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SBI 3U
Ms. Girvan
Genetics Practice Problems
Name: _____________________
Date: ___________________
Instructions: Please complete the following genetics problems on threering binder paper. These are the types of problems you will see on your
test next week.
HELPFUL HINTS:
Purebred = homozygous
Hybrid = heterozygous
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1. A woman who has blood type A is suing a man who has blood type B for paternity. The
woman’s child has blood type O. (a) Can this man be the child’s father? (b) If the man
actually is the father of this child, specify the genotypes of both parents. (c) If it was
determined that it was impossible for the man to be the child’s father, state what the
man’s genotype would be.
2. Red-green colour blindness is controlled by a sex-linked recessive allele in humans. A
woman with normal vision (whose father was colour blind) marries a colour blind man.
(a) What genotypes are possible for the mother of the colour blind man? (b) What is the
probability that the first child from this marriage will be a colour blind boy? (c) What
percentage of the female offspring is expected to be colour blind? (d) What percentage
of the offspring will be normal?
3. In lemmings, there exists a lethal recessive allele for “cliff jumping”. Hybrids do not die;
they are only “puddle jumpers”. Cross 2 puddle jumpers. What is the probability of
having (a) normal lemmings? (b) puddle jumpers?
4. In cattle, the alleles for coat colour displays co-dominance. When a red-coated animal is
crossed with a white-coated animal, the calf produced is roan-coloured (red and white).
Find the offspring when two roan cattle are mated together and state the phenotypic ratio.
5. Sherry, Sheila and Shelley are sisters. Sherry has blood type A. Sheila has blood type
AB. Shelley has blood type O. Their mom has blood type B. Give the genotype of all
three girls and their parents. What is the dad’s phenotype?
6. A naturalist visiting an island in the middle of a large lake observes a species of small
bird with three distinct types of beaks. Those with short, crushing beaks (BB) consume
hard shelled nuts, those with long, delicate beaks (bb) pick the seeds from pine cones, and
those with intermediate beaks (Bb), consume both types of seeds though they are not as
good at either. Assume that this difference in beak morphology is the result of
incomplete dominance. State the phenotypic and genotypic ratios that would result from
a cross between a bird with a short, crushing beak and a bird with an intermediate beak.
7. Use the Pedigree for Trait A to determine the genetic basis of this trait.
a. Does a dominant or recessive allele produce the trait? Explain.
b. Is it autosomal or sex-linked? Explain.
c. What is the genotype of individual IV-2? Explain.
d. What is the genotype of individual IV-6? Explain.