Top Posters
Since Sunday
5
o
5
4
m
4
b
4
x
4
a
4
l
4
t
4
S
4
m
3
s
3
New Topic  
Shamrock Shamrock
wrote...
Posts: 22
Rep: 0 0
13 years ago
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!
Read 3017 times
9 Replies
Replies
wrote...
Staff Member
13 years ago
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
- Master of Science in Biology
- Bachelor of Science
Shamrock Author
wrote...
13 years ago
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?
wrote...
Staff Member
13 years ago Edited: 9 years ago, duddy
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/mdiak (Question 7, scroll down for the answer).

See Attachments:
 Attached file 
Thumbnail(s):
You must login or register to gain access to this attachment.
- Master of Science in Biology
- Bachelor of Science
Shamrock Author
wrote...
13 years ago
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?
Answer accepted by topic starter
bio_manbio_man
wrote...
Valued Member
Educator
Top Poster
Posts: 33224
13 years ago Edited: 13 years ago, bio_man
Sign in or Sign up in seconds to unlock everything for free
1

Related Topics

Shamrock Author
wrote...
13 years ago
That's exactly right.  Thanks for taking a look at it bio_man.
wrote...
Valued Member
Educator
13 years ago
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
Shamrock Author
wrote...
13 years ago
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!
wrote...
Valued Member
Educator
13 years ago
Pleasure.
New Topic      
Explore
Post your homework questions and get free online help from our incredible volunteers
  1144 People Browsing
Related Images
  
 9989
  
 166
  
 82