Class 28

Today in class we learned how to read pedigree charts to predict if the offspring or parents were infected. We were shown many different pedigrees.
We first had to determine whether it was dominant or recessive

First, if there are two parents without the trait, but their children have it, then the gene must be recessive, because if it were dominant, and the two parents both are homozygous recessive, then there is no why their children could have the trait. Their genotype must both be Aa, so that there is a possibility that one child could have the trait.
Note: if, in the second generation, there is an offspring that does not have the trait, and married someone who also doesn't have the trait and have kids that don't have it either, you still cannot be sure that the offspring is homozygous dominant, because there is a chance that they could be Aa.
If you have one parent that doesn't have the trait and one who does, and most or all of their children have the trait, then the gene must be dominant. If most of the offspring have the trait and some don't, then it is still possible that the gene could be recessive, but because MOST have it, it is more likely that it is dominant.
If you have both parents that have the trait, and their children either have the trait or not, then it is most definitely dominant. If it were recessive, then those parents could only ever have children who have the gene. And if they had children who don't have the gene as well, then both parents genotype must be Aa, and the normal children's genotype is aa.

Then we had to determine whether the pedigree was autosomal or sex linked.

 

Sex linked means of the X chromosome. Females have two X chromosomes, so as long as they have one "normal" X chromosome, they would appear normal. Males are XY, so they receive one X chromosome from their mother. If that X chromosome is the "disease" one, then the male is infected. So, a female with the "disease" will ALWAYS give her sons the disease. The pedigree chart will show this. 
A female with the disease will give ONE X chromosome to her daughters. The daughters get the other X chromosome from their fathers. If the father is normal, the daughter will be a carrier only. 
If the father has the disease too, the daughters will ALWAYS have the disease. The pedigree chart will show this also.