00:01
Here we're trying to read pedigrees and figure out probabilities of certain traits being passed on.
00:08
And this is a tree for a recessive trait.
00:11
And we want to sort out how different combinations of people mating might create different probabilities of the trait appearing.
00:24
Okay, so we are to assume that people marrying into the family don't carry the trait and that's proven otherwise.
00:30
So here with number five having the trait, that means number four must be a carrier.
00:43
Okay, so we know that they're going to be a carrier, but otherwise number two, six and eight, we should assume are just going to be homozygous dominant.
01:00
And we also know since number one has this recessive trait, that means both their alleles are going to be homozygous recessive.
01:10
Then all of the offspring that don't show the trait will be carriers and such.
01:22
Okay, so then we're really just being asked questions about the third and fourth generations.
01:27
And so, since we also have five having the trait, we know that dad or great -great -grandpa also has it.
01:46
So if we think about a, we want to look at 3 -1 and 312 and figure out that probability.
02:16
Okay, well, so the parents here were assuming number two is homozygous dominant, which means one -fourth of these genes are the recessive, right? so there's three dominant genes and one recessive one, and there should be then just a one -fourth chance of this point.
02:54
Person having that recessive gene.
03:02
And then here we see, you know, basically half of these parent genes are recessive, right? 50 % of them.
03:13
So it means there's a 50 %.
03:22
I mean, we know that this person is going to be a carrier and all of those aspirins will be.
03:39
Okay, so what we get is one -fourth times one -half is equal to one -eight.
03:52
Okay...
