1 Two black guineapigs are mated together on

1. Two black guinea-pigs are mated together on several occasions and their offspring are invariably black. However, when their black offspring are mated with white guinea pigs, half of the mating result in all black litters and the other half produce litters containing equal numbers of black and white babies. From these results, deduce the genotypes of the parents and explain the results of the various mating, assuming that color in this case is determined by a single pair of alleles.

Answers • BB x BB/BB XBb _ possibly parents genotype X B BB BB b Bb Bb • BB/Bb X bb

2. Two black rabbits thought to be homozygous for coat color were mated and produced a litter which contained all black babies. The F 2, however, resulted in some white babies, which meant that one of the grandparents was heterozygous for coat color. How would you find out which parent was heterozygous?

Answers • Crossing parents with white rabbit • Parents genotype are BB and Bb Crosses Litters genotype BB X bb ------------ Bb X bb ----------

3. What are the possible blood groups likely to be inherited by children born to a group A mother and a group B father? Explain your reasoning.

Answers • AO/AA------------mother • BO/BB-------------father Crosses offspring genotype – AO X BO – AO X BB – AA X BO – AA X BB -------------------------------------------------

• 4. A Woman of blood group A claims that a man of blood group AB is the father of her child. A blood test reveals that the child’s blood group is O. Is it possible that the woman’s claim is correct? Could the father have been a group B man? Explain your reason.

Answers • Mother’s possible blood group genotype – AA/AO • Father’s blood group genotype – AB Crosses Offspring genotype AB X AA -----------AB X AO ------------ • He could not the father

5. A red cow has a pair of alleles for red hairs. A white bull has a pair of alleles for white hairs. If a red cow and a white bull are mated, the offspring are all ‘roan’, i. e. they have red and white hairs equally distributed over their body. a)Is this an example of codominance or incomplete dominance? b)What colors would you expect among the offspring of a mating between two roan cattle?