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tricky F1 cross with specific allele crossover

Genetics as it applies to evolution, molecular biology, and medical aspects.

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tricky F1 cross with specific allele crossover

Postby vulpes » Tue Oct 04, 2011 4:07 pm

Ok at first to me this looks like the simple dihybrid cross which is easy to find the resulting f1 generation. All of the f1 will be heterozygotes but when I do the crossover in the problem during meiosis I the gametes that I get do not match the answers to the problem. I attached the file of me drawing meiosis crossing over of allele a and B.
Image

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It cut out my crossover step. I just had an AaBb and AaBb switch a and B

Problem. Parental organisms of genotypes AABB(paternal) and aabb(maternal) were crossed. Then, meiosis occurred in the F1. In one particular meiotic cell in the F1, the chromosome carrying the maternal a allele segregated with the paternal B allele. In this meiosis, there was no crossing over between genes A or B and their centromeres. The gametes resulting from this meiosis are expected to be?

Ok so what i did as seen in the picture is cross two heterozygotes and during crossover only switch a allele with B allele and left the parental chromosome the same. My resulting gametes came out AB Bb Aa ab. THis cant be correct because on this old test question the options are:
1. AB aB Ab ab
2. AB and ab
3. aB and Ab
4. AB Ab
5. aB AB
Am I messing up in the crossover. Thanks for any help! I am going crazy.
vulpes
Garter
Garter
 
Posts: 6
Joined: Sun Sep 04, 2011 4:36 am

Postby Cat » Fri Oct 07, 2011 1:59 am

F0:

father:

-A-B-------
-A-B-------

Mother:

-a-b------
-a-b------

F1:

All progeny:

-A-B-----
-a-b-----

Meiosis:

-A-B-----
-a-b-----

then

-A-B-----
-A-B-----

-a-b-----
-a-b-----

cross-over:

-a-B-----
-A-B-----

-A-b-----
-a-b-----

Meiosis 1, meiosis 2, ...

answer is 1.
Cat
King Cobra
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