Multiple alleles

Multiple alleles Up until now we have been looking at genes that come in two different forms, e.g. tall (T)or short (t). These different expressions of the same gene are called Alleles. Because each person gets one gene from their mother and one gene from their father an individual always has two alleles. (Except for sex linked traits).

One person carries 2 alleles but………. If you look at an entire population, however, there may be more than 2 kinds of alleles. This type of inheritance is called Multiple Alleles. The one you are most familiar with is blood types. There are three alleles: A B O

Patterns of inheritance: 6 Possible Genotypes 4 Possible phenotypes (Blood type) A A   Type A A O B B Type B B O A B Type AB O O Type O A is dominant over O B is dominant over O O is always recessive A and B are codominant.

A Marley and Justin have 4 children. The father has type A blood A Marley and Justin have 4 children. The father has type A blood. Three of their children have type a blood and one has type O. What is the genoptype of each parent? What is the genotype of each child? Given : offspring have 3:1 ratio and one recessive type O. Therefore each parent must have 1 O. The Justin must also have 1 A. The Marley must also in order to get the 3: 1 phenotypic ratio.

Find the cross that gives a 3 (A): 1 (o) phenotypic ratio Answer: Parents Cross = AO x AO Children genotype= 1 AA: 2 AO: 1 OO Gametes A O AA AO OO