Multiple Alleles In eukaryotic organisms, each individual contains two alleles f

Question

Multiple Alleles

In eukaryotic organisms, each individual contains two alleles for each gene, however more than two alleles may exist in the population. In humans, blood types are determined by a gene having multiple alleles. The allele for A type blood is dominant. The allele for B type blood is also dominant. The allele for O type blood is recessive. A person with type A blood can have the genotype AA or AO. A person with type B blood can have the genotype BB or BO. A person with blood type AB can have the genotype AB. A person with type O blood will have the genotype OO.

Positive and negative factors for blood are determined by a separate gene. This gene is referred to as the Rh factor. We will not consider inheritance of the Rh factor in this activity.

Use the information on Multiple Alleles to complete the following questions.

8. If a man who is homozygous (AA) for A type blood marries a woman who is heterozygous (BO) for B type blood, what blood types will be possible in the children of these parents and what are the probabilities of each of these blood types in the offspring?

Genotypic Ratio –

Phenotypic Ratio –

9. A young woman accuses a male rock star of being the father of her child in a paternity suit. The woman has type B blood; her child has type O blood. The man claims that he could not be the child’s father because he has type A blood. Use the Punnett Square below to show how the man COULD be the father of the child and give genotypic and phenotypic ratios for the results.

Genotypic Ratio –

Phenotypic Ratio –

Explanation / Answer

Answer:

8. Parents: AA * BO

F1: AB, AB, AO, AO = 2 : 2

So, the blood types which are possible in the progeny of these parents are AB and A (AO).

The probabilities of these blood type = 1/2 AB and 1/2 A (AO), i.e 50% AB and 50% A (AO)

Genotypic ratio = AB : AO = 2 : 2

Phenotypic ratio = AB : A = 2 : 2

9. The man can be the father of the child only if both the mother and the father are heterozygous for the individual blood groups.

Parents: BO (Mother) * AO (Father)

F1: AB, AO, BO, OO = 1 : 1 : 1 : 1

So, under heterozygous conditions for both, the genotypic ratio of the progeny can be 1:1:1:1 with 1/4 probability that the child will have O blood group.

Phenotypic ratio = AB : A : B : O = 1 : 1 : 1 : 1

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