What are multiple alleles?

Multiple alleles refer to a gene having more than two allele options, although only two can be present in an individual.

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Why can an individual only have two alleles for each gene with multiple alleles?

An individual can usually still only have two alleles for each gene with multiple alleles because each person typically inherits only one allele from each parent.

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What is an example of multiple alleles in humans?

The ABO blood group system, determined by the immunoglobulin (I) gene, which has three alleles:

IA, IB, and IO.

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How many different blood group phenotypes are there, and what are the genotypes that code for them?

  1. Blood group A - coded for by the genotype IAIO or IAIA
  2. Blood group B - coded for by the genotype IBIO or IBIB
  3. Blood group AB - coded for by the genotype IAIB only
  4. Blood group O - coded for by the genotype IOIO only

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What antigens do the alleles IA, IB, and IO each produce?

  1. The IB allele leads to the production of antigen B on red blood cells.
  2. The IA allele leads to the production of antigen A on red blood cells.
  3. The IO allele does not lead to the production of any antigens.

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Which allele is recessive in the ABO blood group system?

The IO allele is recessive to both IA and IB.

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Which alleles are codominant in the ABO blood group system?

IA and IB are codominant alleles.


This means that both alleles are simultaneously expressed, producing both antigen A and antigen B and the blood group AB.

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