Genetics Question...

[Thomas6]

I stumbled upon a genetics question in a practice PCAT. It reads:

The following phenotypes are seen as a result of a genetic cross: purple flowers smooth seeds, purple flowers wrinkled seeds, white flowers smooth seeds, and white flowers wrinkled seeds. What are the parental genotypes?

a) PPSS x ppss
b) PpSs x PpSs
c) ppss x ppss
d) PpSs x ppss

The answer they give is: "B. the only way to get all four phenotypes (dominant and recessive) is to have both parents heterozygous for both dominant & recessive traits."

But wouldn't D also work?

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[bottlecap1990]

I stumbled upon a genetics question in a practice PCAT. It reads:

The following phenotypes are seen as a result of a genetic cross: purple flowers smooth seeds, purple flowers wrinkled seeds, white flowers smooth seeds, and white flowers wrinkled seeds. What are the parental genotypes?

a) PPSS x ppss
b) PpSs x PpSs
c) ppss x ppss
d) PpSs x ppss

The answer they give is: "B. the only way to get all four phenotypes (dominant and recessive) is to have both parents heterozygous for both dominant & recessive traits."

But wouldn't D also work?

Yes I think so. I tried doing a punnet squares and I got 4 phenotypes
purple smooth, purple wrinkle, white smooth, and white wrinkle.

choice D) PpSs x ppss

possible gametes of PpSs is PS, Ps, pS, ps
possible gametes of ppss is ps

cross these two possible gametes and I got

Genotypes = PpSs: Ppss : ppSs : ppss

purple smooth: Purple wrinkle: white smooth: white wrinkle (1:1:1:1 Phenotypic ratio)

a typo perhaps? is it kaplan?

 

[Thomas6]

Thanks.

It's on the January 2010 Dr. Collin's update (biology, problem #29 I think).

 

[bottlecap1990]

Thanks.

It's on the January 2010 Dr. Collin's update (biology, problem #29 I think).

When are you taking the PCAT?
I'm taking mine next year june 2011.

 

[Thomas6]

August 21st, 2010

 

[roziak]

Got the same answer as well.

Good luck to both of you!