tetrad?

[Dencology]

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.29. A diploid cell (2N = 20) has how many tetrads
at metaphase I?
A. 0
B. 10
C. 20
D. 40

.

 

[ZenoVT]

20

 

[supraman]

I think its 10. A tetrad is 4 chromatids or a homologous pair of chromosomes. So 20 chromosomes lined up at metaphase 1 divided by 2 = 10

 

[Dencology]

i am not sure. lets work on this. anyone out there that would know?

 

[Sea of ASH]

10

 

[ZenoVT]

actually you are right it is 10

 

[bigstix808]

yea, its 10

 

[IDK]

I thought tetrads form at prophase I, do they continue in the metaphase I step?

If it's not 0 then it's 10 for sure😉

 

[bigstix808]

I thought tetrads form at prophase I, do they continue in the metaphase I step?

If it's not 0 then it's 10 for sure😉

tetrads DO form during prophase I. however, they are still tetrads as they are aligned during metaphase I. once anaphase starts, then the answer would be 0

 

[IWantSmile]

10

 

[Dencology]

hey, i still don't get it. One tetrade has 40 chromatides or 20 chromosomes. so what does it mean 2N=20 (i don't understand this part)? does it mean that we have 20 chromosomes?

 

[chessxwizard]

It means that there are 20 chromosomes total, or 10 pairs of chromosomes (like the haploid #). In S phase of meiosis, DNA gets replicated, causing the number of chromatids to double but the number of chromosomes to stay the same. Since homologues pair in prophase, the number of tetrads is equal to the number of chromosomes in the haploid phase, being 10 pairs in this example. If this still confuses you, draw out the replication and pairing to get a better view of what is going on.

 

[Dencology]

so does crossing over increase genetic variation?

 

[supraman]

so does crossing over increase genetic variation?

Prophase I crossing over between to homologs increases genetic variation. (the over lap of the two legs of the chromatids) are called chiasmata.

 

[Dencology]

so why does Kaplan say that it does not?
i don't get it.

 

[supraman]

Kaplan states that crossing over with one sister chromatid with the other sister chromatid of the SAME chromosome will not cause genetic variation, because it is the exact copied material. Only when it crosses with its homolog. If you are rusty on these terms, get those down.

 

[Dencology]

you are right. i got to get it down. thanks for clarification.