00:01
If we know that there are three different genes, e, f, and d, in that order, e and f are 0 .6 map units apart, f and d are 0 .4, what would we expect for all of the different offspring? right, and the individuals that we're crossing, one of them is heterozygous, and so i'm going to say that one of the chromosomes has dominant alleles, and the other chromosome has recessive alleles, and the person we're crossing them with has only recessive alleles on both chromosomes.
00:43
So then, to determine what we would expect for the offspring, we're going to have to individually calculate what we expect for double crossover events, single crossover events, and because we're dealing with three genes, that's single crossover of e to f, and then single crossover of f to d, or two options, and then we will calculate the non -recombinant types.
01:10
So when we calculate all of these, we have to start with double crossovers.
01:14
So in order to do this, we are going to take the recombination frequency of genes e to f, and if they are 0 .6 map units apart, then the recombination frequency is going to be 0 .006.
01:34
We just move our decimal place a couple times to the left.
01:36
So that recombination frequency is 0 .006, and we're going to multiply that by the recombination frequency of f to d, which if the distance between them is 0 .4, then that recombination frequency is 0 .004, and then we'd multiply it by the number of offspring.
02:00
Now, since we're not told how many offspring we should expect in this set of offspring, in this generation, we're just going to multiply it by 100%.
02:11
So that way the answers that we get are percentages, and then you can apply it to whatever you need to.
02:17
And so then we just do that math.
02:20
Right on your calculator, 0 .006 times 0 .004 times 100%, it comes out to a very small number of 0 .0024 % of the offspring should be double crossovers, and we'll come back to that in a minute.
02:36
But next we're going to find out how many should be single crossovers from e to f.
02:41
The way we're going to do that is take the recombination frequency of e to f, and then multiply it by that 100%, and we're going to skip the recombination frequency of f to d, because we don't need to know about those, just e to f, but we will subtract our number of double crossovers, because double crossover includes crossover of e to f, and if we want to look at single crossovers of e to f, we want just the single crossovers, not the double crossovers who have something similar, but extra.
03:12
So then 0 .006 times 100 % minus the 0 .0024%, and it comes out to be 0 .5976 % single crossovers of e to f.
03:27
Single crossovers of f to d are the same thing, we just replace recombination frequency with that of f to d.
03:35
So we're going to multiply that times 100 % minus double crossovers, comes out to 0 .3976%.
03:46
And then lastly, non -recombinant types, we take the total, which is 100%, and then subtract all of the numbers that we've calculated.
03:56
So non -recombinants are just those who don't experience any crossover, they don't experience double crossover or single crossover.
04:02
So we just subtract all those numbers, so 100 % minus the 0 .0024 minus 0 .5976 minus 0 .3976 comes out to be 99 .0024 % non -recombinants.
04:19
And then when we look at each of these different kinds, we can describe them based on the chromosomes of our heterozygous individual, because that will determine their phenotype.
04:29
Since the other individual in this cross has only recessive alleles, they do not determine phenotype...