# Crossing over bio

if crossing over does not occur, how many different gametes can produce an organism with six chromosomes?
A. 8
B.6
C.9
D.infiniite
E. 66

so 2n = 6, n =3. Then to calculate the possibilities it would be 2^n = 2^3 = 8. Hope this helps!

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Heyy!

Just a little question that came to my mind - a chromosome contains 2 chromatids which both have the same alleles, so if we have 6 different chromosomes, doesnt that give us 6 different phenotypes after meiosis?

heyyy! I had the same idea and I chose 6 when I was first solving and the answer key said it should be 8 so that’s why I was confused. I still don’t know why 6 would be wrong

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Hey Darius, The question is finding the possibilities of arranging the number of chromosomes on the metaphase plate during Metaphase 1, since there are TWO chromatids.

During meiotic division, pairing of the homologous pair of chromosomes will take place. So lets say the chromatids are I and II

Each divalent chromosomes will have two possible arrangement.

The two possibilities of arrangements are
I x II
II x I

Hence,

6 chromosomes = 3 bivalents.

Each bivalent has 2 possible arrangements when no crossing over occurs.

Therefore, the possible arrangement of the chromosomes will be 2 x 2 x 2 = 8.

Hence there are 8 possible random ways the bivalents can arrange themselves on the metaphase plate.

I hope this breaks it down properly haha :)) There are infinite possibilities if crossover does occur though.

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Ahh thanks a lot for correcting me Raya, I totally forgot about the independent assortment in meiosis and that each cell will contain 3 chromatids (chromosomes) after meiosis. Makes a lot of sense!

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