Multiple alleles and codominance are important concepts in genetics. The ABO blo
ID: 300272 • Letter: M
Question
Multiple alleles and codominance are important concepts in genetics. The ABO blood groups represent a well-known example of these concepts. Answer the following questions to gain a greater understanding of these concepts:
What blood type(s) can a child born to a mother with B- blood type and a father with A+ blood type have? Explain your answer fully. Be sure to focus on the concepts of dominant and recessive alleles, multiple alleles, and codominance in your explanation.
Are there any special concerns this mother should consider?
How do you think O can be the most common blood type when O is recessive?
Describe another trait in humans that shows multiple alleles.
Although the human population as a whole share the same 29 known blood systems, not all ethnic groups have the same ratios of blood types in their populations. Discuss this fact from an evolutionary perspective.
Explanation / Answer
The child can have A,B,AB or O blood types.Since mother is B - , she could be BB or BO.Similarly, father is A+ ,he could be AA or AO,So, there are 4 possibilities, A,B,AB or O blood type for the child.If IA allele gives A blood type , IB allele gives B blood type and i allele gives O blood type, then it should be notes that IA and IB are dominant over i.
Special concerns for the mother : Since the mother is Rh- and father is Rh + , the child will be Rh +.During pregnancy, the mother's immune system will recognise the Rh protein in the foetus blood as foreign and start producing antibodies against it.This could cause birth defects in the child , miscarriage and death.Usually the first pregnancy is not affected to much extent as the mother is not exposed to the foetus blood till delivery.However the antibodies already prepared in the mother's blood could cause future miscarriages when pregnant.So the mother should avoid future pregnancy after the birth of the first child.
O is the most common blood type when O is recessive because i, IA and IB alleles do not occur in equal frequency.Also,i allele is more commonly found than IA or IB .ii pairing occurs more frequently than iIA or iIB pairing as a result of which O becomes the most common blood type.
Another trait that shows multiple alleles is the hair color.In this case, different alleles do not express dominance over each other but they express strongly than others as a result of which the hair color varies.
From an evolutionary perspective, it can be said that migration and distribution of human population leads to variation that in turn results in different ratios of blood types in their populations.
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