Got Milk? Pedigree Charts 

We use pedigree charts to figure out whether the gene of interest is dominant or recessive, and sometimes whether it is on an X or a Y chromosome (which is called sex-linked). In this lesson we will focus on a family that has either a dominant or a recessive mutation affecting their digestion of milk.

You will need to review the Punnett Square activities from the previous classes. The vocabulary of pedigree charts is slighty different. A heterozygous individual with a recessive mutation is called a carrier, because although they do not show the mutation, their children may.

Heritage pattern hints

Look to see if two parents without a trait have a child with the trait. We will explain that next:

If two parents do not show the trait and have a child who does, then the trait is almost certainly a recessive trait and the parents are heterozygous carriers.

It is unikely that a child showing a dominant trait is born to parents who both do not show the trait. This is because one or both parents would have to have passed down the trait to the child, so would have to have at least one allele with the dominant trait. And so this parent would show the trait since it is dominant. Which contradicts what happened.

The only way these scenarios are not true is if an entirely new mutation happened, and we assume that this does not occur in our pedigree charts.