1. Multiple Alleles

2. What are multiple alleles Sometimes more than two different alleles exist for a given gene. This condition, known as multiple alleles, explains the existence of the four most common human blood groups. The blood group gene has three alternative alleles – I A (A), I B (B), i or I O (O) that form the ABO blood grouping system. The inheritance of human blood groups shows multiple alleles expressed as complete dominance and co-dominance.

3. I A and I B are co-dominant. I A and I B are both completely dominant to i. GenotypePhenotype I A A I A i (or I A I O )A I B B I B i (or I B I O )B i i (or I O I O )O I A I B AB

4. Feather colour in chickens Feather colour in chickens is controlled by the three following dominant alleles and seven recessive alleles: E, E R, E R – Fayoumi, e Wh, e +, e b, e s, e bc, e y and e q. Each individual chicken still inherits only two alleles for this gene. However, having multiple alleles increases genetic variation in chickens. With a number of different alleles for a gene in the gene pool, an individual can show one of several phenotypes and not just one or two phenotypes as is the case with complete dominance.