AQA Biology 2010 A-Level Question (Meiosis)

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User148
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Hi,

It's always questions like these where I get confused...

It's question 5dii here: https://mathsmadeeasy.co.uk/wp-conte...W-QP-JUN10.pdf

The answer is 8, but I don't really understand why.

If I name the gametes A, B, C (maternal) and a, b,c (paternal) then my combinations will be as follows:

A (B or b) and (C or c)
B (A or a) and (C or c)
C (B or b) and (A or a)

a (B or b) and (C or c)
b (A or a) and (C or c)
c (B or b) and (A or a)

So this is where I'm up to with my working and I'm not sure where to go to from here.

I'm guessing the working is 2 to the power of 3? But I still don't understand that. For some reason, I can't really grasp the principle.

Would really appreciate your help!
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luckybillion
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(Original post by User148)
Hi,

It's always questions like these where I get confused...

It's question 5dii here: https://mathsmadeeasy.co.uk/wp-conte...W-QP-JUN10.pdf

The answer is 8, but I don't really understand why.

If I name the gametes A, B, C (maternal) and a, b,c (paternal) then my combinations will be as follows:

A (B or b) and (C or c)
B (A or a) and (C or c)
C (B or b) and (A or a)

a (B or b) and (C or c)
b (A or a) and (C or c)
c (B or b) and (A or a)

So this is where I'm up to with my working and I'm not sure where to go to from here.

I'm guessing the working is 2 to the power of 3? But I still don't understand that. For some reason, I can't really grasp the principle.

Would really appreciate your help!
Hi,
I'll try my best to explain where you've gone wrong.
In your working you seem to assume that the maternal and paternal chromosomes are the same. for example
A (B or b) and (C or c). this is not one combination as it can be ABC, ABc, AbC, Abc
I'm sure if you went and wrote out each combination and then excluded repeats/equivalent combinations your answer would be 8
A B C
A B c
A b c
A b C
a B C
a B c
a b C
a b c

But writing out each combination can be a long process and I wouldn't recommend it, especially in a question with more chromosomes.

Instead we can look at it mathematically.
there is the formula 2^n for the possible combinations of chromosomes in gametes
where n is the number of chromosomes per gamete.
In this case n would be 3. 2^3 = 8 possible combinations


If you want more help or want to understand something/the formula further, I'll give it a shot
Hope this helps
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