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OCR A Biology

I^A I^B Multiple Alleles Results Prod I^O Gene

Multiple alleles occur when more than two alleles exist for a gene within a population, though an individual only possesses two. Blood groups, determined by codominant alleles I^A and I^B and recessive allele I^O, exemplify this, leading to blood types A, B, AB, and O based on allele combinations.

Multiple alleles exist when a gene has more than two allele forms in a population, although an individual only carries two. Human blood groups are an example, determined by alleles I^A, I^B, and I^O. I^A and I^B are codominant, while I^O is recessive. Blood types are A (I^A I^A or I^A I^O), B (I^B I^B or I^B I^O), AB (I^A I^B), and O (I^O I^O).

Front multiple alleles
Back
  • some genes coded for by multiple alleles (more than 2) but organism can only carry 2 versions of the gene (one on each homologous chromosome)
  • blood group determined by immunoglobulin gene has multiple alleles that code for diff antigens on RBC surface, I^A allele results in prod of antigen A, I^B allele results in prod of antigen B and I^O allele results in prod of neither antigen, I^A and I^B are codominant and I^O recessive, different combos of blood groups are;
  • A (I^A I^A or I^A I^O)
  • B (I^B I^B or I^B I^O)
  • AB (I^A I^B)
  • O (I^O I^O)

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