00:01
Starting with a parental cross between homozygous dominant and homozygous recessive, the proportion of heterozygous in the f2 generation progeny will be.
00:13
So anytime you cross a homozygous dominant with homozygous recessive, all of the children are going to be heterozygous because the homozygous dominant parent only has a dominant allel to give, and the homozygous recessive parent only has a recessive allel to give.
00:31
So each offspring is going to get one dominant from the dominant parent and one recessive from the recessive parent.
00:39
So then what proportion of heterozygous in the f2 progeny will be? so we are, so we're crossing two offsprings from our first cross, our f2 generation, which we've talked about was heterozygous.
00:54
So if we just do a quick, punnet square, and it says what proportion are heterozygous? this one here and this one here.
01:11
That is two out of four of our children, or one half.
01:17
So looking through our answers, letter d is the correct answer.
01:24
Mating two organisms produces a three to one ratio of the phenotype in the progeny.
01:30
The parental genotypes are.
01:32
So we're looking at phenotype, not genotype.
01:39
And taking a quick glance through our answers, looking at the last two, when you cross these two homozygous dominant, the only offspring you're going to get are the exact same.
01:50
We're homozygous dominant because every offspring is going to get a dominant allele from both parents.
01:57
So all of the offstrings are going to be the exact same.
02:00
So therefore, it's going to be a four to zero ratio.
02:04
We can mark off this one and it's the same with letter e, except they'll be recessive instead of dominant...