00:01
You have two genes, three genes involved, b, pr, and vg.
00:08
B stands for the black body.
00:10
So black is recessive to gray body, b+.
00:14
Then you have another gene, pr +, stands for the red eye, dominant to pr, purple eye.
00:33
And then you have vestigial wing, vg +, which is the normal wing, dominant to the vestigial wing, vg.
00:42
And we know that these three genes somehow are map distance and linked.
00:53
B to pr has six map units, and pr to vg, 13 map units.
01:05
Now we know that the interference between the two genes is 0 .5.
01:11
And now we have a cross.
01:12
The fly with black body, purple, vestigial wing, basically they are triple recessive.
01:17
It's crossed with a fly homozygous for gray body, red eye, and normal wings.
01:22
So for the parent generation, you have a homozygous wild type, b +, b +, purple +, purple +, and vg +, vg +, crossed with all recessive.
01:51
Then all the f1 will be the heterozygous.
01:56
So this female obviously pick up one allele from each of the parents, so that this is why f1 is a heterozygous for all three genes, b, pr, and vg.
02:14
So this female crossed with a male that have all three homozygous recessive, lower b, pr, and vg homozygous, all recessive.
02:33
So the question asks you about out of the thousand progeny produced from this cross -cord, what will be the phenotype and portion of the genotype, not progeny.
02:45
So let's take a look at the phenotype.
02:48
So obviously there are two type of f2.
02:54
One we call parental.
03:00
The parental progeny basically come from the non -crossover gametes.
03:05
Because these three genes are linked, sometimes there is crossover between the b and pr or pr and vg, but most of the time there's no crossover.
03:18
So it will keep the same as their parents.
03:21
So that's why we call it parental.
03:23
So if you look at the distribution of the gene or the arrangement of the gene, you can tell that this is the f1, b +, pr +, and vg+.
03:37
This is on one of the chromosomes.
03:39
And then the other chromosome is b, pr, and vg.
03:44
And of course it crossed with the other parent, all three recessive, b, pr, vg, b, pr, and vg.
03:58
So again, you can see that they have no crossover between the two genes.
04:02
So it will produce two type of parental progeny.
04:06
So again, these are still the f1 parent.
04:10
So now you can see that each will give out one of the chromosomes.
04:15
This is a haploid gametes.
04:17
So the progeny that will come out, let me move it down there.
04:28
The f2 will either be b +, pr +, vg from the f1 female and then pick up another allele from the male, lower b, pr, and vg.
04:48
Or it will get the other chromosome, b, pr, or vg from f1, then the other chromosome from the male, triple recessive male, b, pr, and vg.
05:06
So these two are called parental because if you look at the phenotype and genotype, they look exactly like their parents in f1.
05:15
So you can see that they're identical.
05:17
So these two, that's why we call them parental.
05:21
And they're usually more common.
05:23
Now the second category of f2 come from the crossover.
05:29
We call this recombinant.
05:33
There will be crossover.
05:37
So basically, the idea is that you have a crossover between the b, pr, or pr, vg.
05:45
So there are different crossovers.
05:48
You have single crossover between b, pr, pr, and vg.
05:52
Or you can have double crossover, both b, pr, and pr, and vg.
05:56
So let's take a look.
05:58
So you will have a single crossover between the b and pr.
06:08
So you'll have b +, pr, vg.
06:18
And then the other is b, pr +, and vg+.
06:27
This is a single crossover between b and pr.
06:34
And as a result, it will produce two type of f2.
06:44
This is f1.
06:50
The other parent is still the same, triple recessive.
06:59
So you can see for f2, single crossover is going to produce b +, pr, vg, b, pr, vg.
07:17
Or b, pr +, vg +, and b, pr, and vg.
07:34
So this is a single crossover between the b and pr.
07:44
And then also there will be a single crossover between pr and vg.
07:52
So in that case, same thing.
07:55
You have a crossover between these two.
07:58
So now the f1 is going to look like this.
08:02
B +, pr +, but vg.
08:18
And then the other chromosome is b, pr, vg+.
08:24
Then it cross with again the triple recessive male.
08:36
The f2 will be b +, pr +, vg, b, pr, vg.
08:53
Or b, pr, vg +, b, pr, vg.
09:14
So this is a single crossover between the later two genes.
09:19
And then lastly, you have double crossover.
09:23
So eventually all three, sort of, you can see that you have double crossover between b and pr and pr and vg.
09:31
And as a result, the f1 is going to look like b +, pr, vg +, b, pr +, vg.
09:46
Then it cross with the parent triple recessive.
09:52
You get f2 double crossover...