00:03
So you can see here in this pedigree, i've only drawn part of it because we only need part of it to solve the answer.
00:08
So here we have a few different families.
00:11
We have the grandparents up here and all of their offspring, these four children.
00:18
So what we see with this family is that we have one parent who has the trait and some of the offspring who also have the trait.
00:26
Now, if we're looking to see, you know, how is this trait inherited? this family up here with the grandparents and the parents is a really good place to start because we see that the dad has the trait and the mom does not but when we look at the children some of the girls have it some of the boys have it and some girls some boys don't so that tells us that this trait is likely to be autosomal because if say this was a sex link trait it would either be a y linked trait where only boys could have it but we see that here a girl has it so that can't be the case or or it would be an x -linked trait.
01:03
Now, if it was x -linked, that means that mom doesn't have it, and so couldn't pass it on, but dad does.
01:11
And only the girls would receive an x from dad, right? but since we have dad who has it and a son who has it, then this is probably not sex -linked.
01:21
It is rather autosomal.
01:23
So then, once we know that, we can compare that family with the grandparents and the parents to this family down here.
01:33
So we see that in the grandparents and parents, one of the parents has the trait and some of the offspring do.
01:42
But when we look at this new family down here, neither of the parents have it and neither of the children do, which means that this trait is likely a dominant trait because we can have a situation where some parents have it and so could pass it on but some parents don't, and that does not change the outcome, right? because if, say, a parent was dominant, then their children were going to dominate from them, and it could mask getting the recessive from the other parent.
02:17
But over here, we have two parents who do not have the trait and their children can't have it, then that means that both parents are recessive and they could not be carriers, therefore they can only give offspring recessive and all their offspring have to receive recessive from them.
02:34
So we're most likely looking at a dominant autosomal trait.
02:40
So once we know that, we can go through and determine genotypes of all the people involved.
02:45
Now, it's easiest to start with individuals who do not have the trait because we know they are homozygous recessive...