00:01
Hey there.
00:02
So to recap briefly, drosophila eye -color genetics is x -linked, meaning that it is found on only the x chromosome, and as such, the sex of the drosophila and any offspring it may have, is tied in a way to some degree to the phenotype that is displayed by eye -color genetics.
00:24
So to recap, the wild type eye color for drosophila is red as represented here.
00:33
And of course, this is the dominant allele, meaning you only need one copy of this in order to display the phenotype of red eye color.
00:41
In contrast, the recessive equivalent would be white eye color, which you need, of course, two copies of this allele in order to display the phenotype.
00:49
So with all that in mind, let's take a look at the reciprocal cross that was mentioned between, the white -eyed female and the red -eyed male.
01:00
Of course, if it's a white -eyed female, the only possible genotype would be this, since it's a recessive allele.
01:09
And now incorporating this into our punnet square, we have for the red -eyed drosophila male, the only possible genotype would be this.
01:21
Since males have a y chromosome taking the place of the second x chromosome, the only the determining factor of the drosophila's eye color would have to be that singular x chromosome and whatever allele came along with it.
01:34
And since the eye color is stated to be red, we can safely assume that this drosophila male would have this particular genotype.
01:45
So taking a look at the offspring that this cross produces, we have for the females, this genotype, and for the males, this genotype.
02:07
Again, so we have a roughly 50 to 50 ratio or one -to -one ratio of the f1 progeny being female and male, and among the females, all of them would have red eyes due to the fact that the dominant red -eye color allele would take precedence over the white eye colored allele.
02:27
And so what we end up with here is half of the total offspring, that is, being red -eyed females.
02:38
Down here for the males, since the only x chromosome that's influencing anything is one with a white eye color allele, we can safely say that we end up with all of the male offspring being white -eyed.
02:55
And so this is pretty consistent with what the problem tells us.
02:58
The problem says that in the reciprocal cross, we have half of the offspring of the f1 progeny being red -eyed females and the other half being wide -eyed males.
03:08
Now that we have that in mind, let's go back to the original question that was being asked.
03:14
What happened when a red -eyed female is being crossed with a white -eyed male? the white -eyed male's genotype is pretty easy to figure out again, because the fact that they only have one x chromosome to deal with being the determining factor, and since it's white -eyed, that means that the only x -chromosome that this male has has to contain the white -eye color allele.
03:38
Now drawing a punnet square for...
