Codominance
In many ways Gregor Mendel was lucky in discovering his genetic laws because they happened to have a number of easily observable traits. When studying he thought that one allele happened to be dominant & the other recessive. Though, things aren't always so clear-cut & "simple," such as Codominance.
Codominance is a relationship between two versions of a gene. Individuals receive an allele from each parent. If the alleles are different, the dominant allele usually will be expressed, while the effect of the other allele, called recessive, is masked. In other words, codominance is a homozygous individual. In codomiance you will find that an individual can get, for example, black fur, white fur, or black AND white fur. In many cases you will find that codominance problems have to do with blood type and before starting any blood type problem you should know the following : Type A blood --> AA or Ao Type B blood --> BB or Bo Type O blood --> OO Type AB blood --> AB |
Here is a sample problem for Codominance:
If a man with type O blood marries a woman with type AB blood, what will be the expected blood types of the offspring? Unlike Mendelian Genetics, we don't need to know which trait is dominant or recessive because codomiance is already all homozygous dominant. So, the man with type O blood is homozygous dominant and the woman with type AB blood is also homozygous dominant. Now that we know this information, we have to put it into a punnett square to find the expected blood types of their children. After completing the punnett square, we need to write the ratios for genotype and phenotype. Possible genotypes are AO, BO, or O and possible phenotypes are type B, type A, or type O. According to this square, there is a 50% chance that the offspring will be type A blood and a 50% chance that it will be type B blood.
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