Biology Forums - Study Force

Here are the crosses:

1) Albino 1 x Black
F1 = all black
F2 = 3 black
1 albino

2) Albino 2 x Agouti
F1 = all agouti
F2 = 3 agouti
1 albino

3) Agouti x Black
F1 = all agouti
F2 = 3 agouti
1 black

4) Albino 2 x Black
F1 = all agouti
F2 = 9 agouti
3 black
4 albino

5) Albino 1 x Agouti
F1 = all agouti
F2 = 9 agouti
3 black
4 albino

I deduced that the mice have the following genotypes:
Albino 1: aabbcc
Albino 2: AAbbcc
Agouti: AAbbCC
Black: aaBBCC

Is this correct?


Also, I am really unsure about the genotypes I predicted at the B locus.  Could someone please just explain which crosses I need to look at and why in order to deduce the genotype at this locus?

Thanks!

Albinism is an autosomal recessive condition (so aa).

1)

     a    a
A  Aa  Aa

A  Aa  Aa

All Black, 0 Albino

    A   a
A Aa Aa

a Aa aa

3 Black, 1 albino

What do you mean about Albino 2

Ok, I am actually looking to predict the genotype of the mice at 3 different loci (A, B, and C) not just one. 

The pathway goes C -> A -> B.  C stands for colorless, A stands for agouti, and B stands for black (in this experiment).  If the mouse has a dominant C, it can show color.  If it has two recessive alleles at C, it is albino.  If a mouse has a dominant C and a dominant A, it is agouti.  If a mouse has at least one dominant C and both recessive A's and at least one dominant B, it is black.   

So, in summary, with these five crosses, I need to figure out the genotype for every one of the parent mice (agouti, black, albino 1, and albino 2) at all 3 of the loci (A, B, and C).  My guesses are:

Albino 1: aabbcc
Albino 2: AAbbcc
Agouti: AAbbCC
Black: aaBBCC

But I don't know if these are correct.  I do KNOW for sure that the genotypes of the 4 mice at the A and C loci are correct, but I am really just looking for someone to help with the B locus.  Can someone please help me figure this out?

K, I'm not totally sure but I tried to find some sources that may help you to answer these questions:

http://tiny.cc/ly5sx (http://tiny.cc/ly5sx)

http://tiny.cc/mdiak (http://tiny.cc/mdiak) (Question 7, scroll down for the answer).

See Attachments:

Ok, so after looking again at the albino 2 x black cross, I can deduce that both parents are homozygous dominant for the B locus or else there would be variation in the F2 generation (black and brown mice, not just black).   


So now all that I am looking for is the genotype at the B locus for albino 1 and agouti.  Anyone know how to figure this out?

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That's exactly right.  Thanks for taking a look at it bio_man.

Okay, I asked a friend of mine who studies genetics.

They said if you have the parental line aaBBCC x AABBcc, in the first gen. you get aABBCc (All agouti). In the F2 generation, you will get 9 agouti, 3 black, and 4 albino. I'm not a geneticist so maybe you can make sense of these numbers and explain them to me?

This is if locus A is agouti, locus B is black, and C is albino...

She also mentioned that

Alleles at A and C interact (called epistasis in genetics):

- If the mouse is aaCx it is not agouti and not albino (in our case a black mouse)
- If the mouse is AxCx it is agouti and not albino
- If the mouse is xxcc it is albino no matter what the alleles at the agouti locus are because they are irrelevant

Thanks!  That makes a lot of sense to me.  The phenotypic ratio that you get in the F2 generation is just because of epistatic interactions.  Thus, instead of the 9: 3 : 3 : 1 ratio that you would normally get, there is a 9 : 3 : 4 ratio because the gene at the C locus is epistatic over the other genes at the A and B loci.  I assume that, because of the similar ratio in the agouti x albino 1 cross, those parents must also be homozygous dominant for B or else we would see some brown mice in the F2.

Thanks for the help bio_man!

Pleasure.