In german cockroaches curved wings c v are recessive to...

In German cockroaches, curved wings $(c v)$ are recessive to normal wings $\left(c v^{+}\right) .$ A homozygous cockroach having normal wings is crossed with a homozygous cockroach having curved wings. The $\mathrm{F}_{1}$ are intercrossed to produce the $\mathrm{F}_{2}$. Assume that the pair of chromosomes containing the locus for wing shape is metacentric. Draw this pair of chromosomes as it would appear in the parents, the $\mathrm{F}_{1}$, and each class of $\mathrm{F}_{2}$ progeny at metaphase I of meiosis. Assume that no crossing over takes place. At each stage, label a location for the alleles for wing shape $\left(c v \text { and } c v^{+}\right)$ on the chromosomes.

Transcript

00:01 All right, so reported to answer this question, there are actually two pieces of information you need to know first.

00:07 First is the shape of the chromosome.

00:10 It tells us that the chromosomes are metacentric, and so this just means that the centromere is located right in the middle.

00:20 So of these four types of chromosomes, it is the metacentric type.

00:27 And then secondly, it asks you to draw what they, would look like during the metaphase 1 part of myosis.

00:38 So if we go back over mitosis and meiosis, mitosis you start and finish with the essentially identical cells.

00:46 They're pretty much exactly the same.

00:49 Myosis, you're going to half the number of chromosomes in the cell.

00:54 So during myiosis 1, we have crossing over, we have the homologous pairs separate, and we end with half the number of chromosomes.

01:03 And then myosis 2, you just have sister chromatid separate and it's really close to essentially what happens in mitosis.

01:11 So, myosis 1, in order for crossing over in homologous pairs to separate, you have your chromosomes lined up right next to each other and they're metacentric, so they will look like this, more or less, with their centrimures in the middle.

01:31 And then, you're, and different parts on the same chromosomes will overlap.

01:37 But this question says that assume no crossing over appears.

01:42 So now we know that is the formation the chromosomes will be in, and this is their shape.

01:51 So let's go ahead and look at what we're dealing with.

01:57 So it says one of the parents is homozygous for curved wings, and one is homozygous for normal wings.

02:06 So we're just going to label that here.

02:09 One parent is homozygous, cv, cv, for curved wings, which doesn't have a plus.

02:16 And then one is homozygous for normal wings, which has a plus.

02:24 And says the curved wings are the recessive one.

02:26 So i'll just put an r for recessive.

02:29 So over here we have our cross.

02:31 So they're offspring because both of these are homozygous.

02:35 They will get one copy of each.

02:45 Cv, cv, cv plus, cv plus.

02:51 And so all their offspring will have the dominant trait because they don't have two of the recessive trait.

02:55 So all of their offspring will have normal wings...

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