Biology Question (1 Viewer)

[Khan.Paki]

Hey guys,

Can someone please help with part (b) in this question. Keep getting confused.

Cheers

 

[Fiction]

A, B, a and b are all alleles. An allele is just a gene found on homologous chromosomes, in corresponding positions or loci.
So possible combinations of alleles in that question could be: Ab, AB, aB or ab

 

[Mr_Kap]

A, B, a and b are all alleles. An allele is just a gene found on homologous chromosomes, in corresponding positions or loci.
So possible combinations of alleles in that question could be: Ab, AB, aB or ab

sucess one has: BD, bD, ae, Bd,bd, AE

 

[Mr_Kap]

anyone know which answer is correct for part 2.

 

[Flop21]

What is actually happening here? a)? They've lined up ready to split... only one pair of chromosomes have 'crossed over'? So then cell splits, then splits again, resulting in 4 haploid daughter cells.

So then the combination would just be AB, Ab... etc. ?? Or have I missed something above??^

 

[Fiction]

sucess one has: BD, bD, ae, Bd,bd, AE

Oh opps, I didn't read the question properly. The diagram shows 2 stages of meiosis. You look at the second diagram. I haven't touched this in a while but basically in meiosis (and mitosis) your chromosomes/ chromatids swap alleles (crossing over), line up on the equator, then get pulled apart by chromosomes. The difference between mitosis and meiosis simplistically, is that in meiosis this process repeats again so you end up with 4 haploid cells from 1 parent diploid cell. You also don't get crossing over happening during mitosis.

From the sounds of things, you're just looking at the crossing over process in this question. So basically get corresponding chromosomes, mentally line them up, then get any allele combination. Essentially you're doing the same thing the question has done from the first diagram to the second diagram. Notice how in the first diagram all allele combinations are all caps or all lowercase, then in the second diagram you have cases of one cap and one lowercase letter combinations? (Bb) Just do that.

 

[Flop21]

Oh opps, I didn't read the question properly. The diagram shows 2 stages of meiosis. You look at the second diagram. I haven't touched this in a while but basically in meiosis (and mitosis) your chromosomes/ chromatids line up on the equator, swap alleles (crossing over), then get pulled apart by chromosomes. The difference between mitosis and meiosis simplistically, is that in meiosis this process repeats again so you end up with 4 haploid cells from 1 (or two, I can't remember) parent diploid cell.

From the sounds of things, you're just looking at the crossing over process in this question. So basically get corresponding chromosomes, mentally line them up, then get any allele combination. Essentially you're doing the same thing the question has done from the first diagram to the second diagram. Notice how in the first diagram all allele combinations are all caps or all lowercase, then in the second diagram you have cases of one cap and one lowercase letter combinations? (Bb) Just do that.

Why has only 2 chromosomes crossed over in diagram? Do not all chromosomes cross over?

 

[Fiction]

Why has only 2 chromosomes crossed over in diagram? Do not all chromosomes cross over?

I don't have the faintest clue; I haven't touched blueprint of life in a very long time lol. The only reason I can think of why not all chromosomes may cross over is because you get more genetic diversity that way. And since meiosis is all about variation, it seems plausible. But that's assuming not all chromosomes cross over.

TBH I'm more curious about why there's a BD in variation. Assuming b is the corresponding allele of B, how can D be also a corresponding allele of B? To my understanding, alleles are variations of genes on corresponding positions on homologous chromosomes. That implies there's only 2.

 

[Fiction]

I don't have the faintest clue; I haven't touched blueprint of life in a very long time lol. The only reason I can think of why not all chromosomes may cross over is because you get more genetic diversity that way. And since meiosis is all about variation, it seems plausible. But that's assuming not all chromosomes cross over.

JOKES
I lied.
I didn't read the question properly (yet again); soz haha

Basically the question has shown you when prophase - metaphase 1 occurs (line up at equator). It's asking you what the resulting 4 daughter cells would look like, provided diagram 1/ circle 1 is the parent cell. So you know that in meiosis, 1 parent cell = 4 daughter cells. Therefore prophase, metaphase, telephase all occur twice in meiosis.

The second diagram shows a cell about to undergo anaphase/ being pulled apart by the spindles to opposite poles of the cell where telephase can occur and you get two cells. Essentially the left side of the second cell = one new cell, and the right side of the second cell = another new cell. Therefore you can't have AA and Bb crossing over with aa Bb for example (since they aren't going to be in the same cell)

Taking the left side of the second diagram for example, since AA Bb and EE, DD are all alleles that are going to be in one cell. Since you know in meiosis, a second propase, metaphase and telephase occurs, during the second crossing over process, AA will switch with EE and Bb will switch with DD, so you end up with AE, AE, BD and bD. Which comes down to 3 combinations since AE is a repeat.

Then do the same with the right side of the second diagram and you get your answer