TPR-Genetic Recombination

[G1SG2]

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From the TPR Genetics chapter:

"The height and color gene in pea plants are on the same chromosome as a third gene for big or small flowers. The alleles of flower size are a dominant B (big) and recessive b (small). The color gene (G, green or g, yellow) is studied in relation to the flower size gene. In the first cross, pure-breeding homozygous BBGG plants are crossed with bbgg plants. If a small flower green plant is observed in the F1 generation, was recombination responsible?"

Answer: The small flower green phenotype could not be produced by recombination. These alleles do not exist together in either parent and so could not be recombined together in the gametes. This must be the result of mutation.

Uh, why can't this be attributed to genetic recombination? Of course these alleles do not exist together in either parent-that's why it's called recombination?

 

[matth87]

Recombinant phenotypes would be pea's that do no exhibit the same phenotype as their parents. There is also another part to this definition. These recombinant must still lay within the boundries of the expected ratios.

Parent:
BBGG x bbgg
- Expected Ratio in F1 - 1
- The only possible genotypes are BbGg
- All of these will be Big and Green so there are no possible chances for any recombinants in this cross.
- Any varying phenotypes must be mutations, since it is impossible to get anything other then BbGg.

F1 Cross:
BbGg x BbGg
- Expected Ratio in F2 - 9:3:3:1
- 9 will be Big and Green
- 3 will be small and Green
- 3 will be Big and yellow
- 1 will be small and yellow
- The small/green and big/yellow are recombinants because they fall with in the expected ratios but do not exhibit the same phenotype as the parents.

If the recombinants display ratios that vary from the 9:3:3:1 then you can think of it like the genes are sticking together preventing recombination and this is caused by linkage of genes.

Hope this helps. Stop trying to think about it so hard haha I bet your head is about to explode. Yeah genetics can be very confusing until you get all this **** straight in your head.

 

[G1SG2]

Recombinant phenotypes would be pea's that do no exhibit the same phenotype as their parents. There is also another part to this definition. These recombinant must still lay within the boundries of the expected ratios.

Parent:
BBGG x bbgg
- Expected Ratio in F1 - 1
- The only possible genotypes are BbGg
- All of these will be Big and Green so there are no possible chances for any recombinants in this cross.
- Any varying phenotypes must be mutations, since it is impossible to get anything other then BbGg.

F1 Cross:
BbGg x BbGg
- Expected Ratio in F2 - 9:3:3:1
- 9 will be Big and Green
- 3 will be small and Green
- 3 will be Big and yellow
- 1 will be small and yellow
- The small/green and big/yellow are recombinants because they fall with in the expected ratios but do not exhibit the same phenotype as the parents.

If the recombinants display ratios that vary from the 9:3:3:1 then you can think of it like the genes are sticking together preventing recombination and this is caused by linkage of genes.

Hope this helps. Stop trying to think about it so hard haha I bet your head is about to explode. Yeah genetics can be very confusing until you get all this **** straight in your head.

OHH lol, okay I get it now. Thanks! Hahaha, I'll try not to think about it so hard, but you know sometimes that's impossible