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Help with Phenotype and Genotype.?

In this packet I got from my teacher (I’m in 9th grade), and I received a packet containing questions such as the following:

In poultry, rose comb is controlled by a dominant allele and its recessive allele controls single comb.
a. Give the genotype and the phenotype produced from crossing a pure-breeding rose comb chicken with a pure-breeding single comb chicken.
b. Give the results of the backccross of the F1 hybrid with both pure-breeding parents.

Guys, I’m so lost! Could someone thoroughly explain this whole process to me?
My packet was just questions, no explanation or anything.
Thank you so much erin!

This is a pretty common question type. It’s governed by the Punnet square, which I’ll describe below.

First, rose comb, since it’s dominant, we’ll abbreviate as ‘R’ and single, since it’s recessive, we’ll abbreviate as ‘r’. So a pure bred dominant would have a genotype (the way the genes look) of RR while a purebred recessive would have a genotype of rr. When we cross these, we have to do the Punnet square:

R R
r Rr Rr
r Rr Rr

Can you see from the above that when a RR combines with an rr, you get four possibilities: Rr, Rr, Rr and Rr. Therefore, the genotype of all the young, or the F1 generation, would be Rr while the phenotype (the way it looks) would be rose colored since the R is dominant!

Next: We’ll cross the F1 generation (the Rr) with the pure bred parents, to keep it simple, we’ll put the F1 generation on the top of the Punnet square and the parent on the left (although you can reverse these, it doesn’t matter)

The pure bred dominant (RR)

R r
R RR Rr
R RR Rr

So here, you have two possible genotypes: RR and Rr, both will have the same phenotype.

The pure bred recessive (rr)

R r
r Rr rr
r Rr rr

You see that when you cross the F1 with the recessive pure bred, you get two possible genotypes: Rr and rr, but now you have two phenotypes: rose and single comb.

Hope this helps!

4 thoughts on “Help with Phenotype and Genotype.?

  1. agarcia says:

    rose comb dominant A
    single comb recessive a

    a)genotype
    pure breed rose comb AA
    pure breed single comb aa
    =Aa
    phenotype is the description.
    =rose comb

    i’m not too sure about b so i don’t want to try and do it wrong. there should be something in your packet it about it.
    References :

  2. cathaychris says:

    phenotype = observable trait, genotype = actual alleles
    Let’s call rose comb ‘R’ and single comb ‘r’.
    a.
    You’re crossing pure-breeding rose comb (RR) with single comb (rr). That’s RR x rr which produces, after drawing a Punnett square or doing it in your head, all Rr (only one possible gamete per mate). The genotype is Rr, but the phenotype (what you see) is rose-combed, because the dominant allele takes over.
    b.
    This question is a little confusing. Do you mean the cross of Rr x Rr? If so, there will be 1/4 RR, 1/2 Rr, and 1/4 rr. That’s 3/4 rose comb and 1/4 single comb.
    References :

  3. erin62178 says:

    This is a pretty common question type. It’s governed by the Punnet square, which I’ll describe below.

    First, rose comb, since it’s dominant, we’ll abbreviate as ‘R’ and single, since it’s recessive, we’ll abbreviate as ‘r’. So a pure bred dominant would have a genotype (the way the genes look) of RR while a purebred recessive would have a genotype of rr. When we cross these, we have to do the Punnet square:

    R R
    r Rr Rr
    r Rr Rr

    Can you see from the above that when a RR combines with an rr, you get four possibilities: Rr, Rr, Rr and Rr. Therefore, the genotype of all the young, or the F1 generation, would be Rr while the phenotype (the way it looks) would be rose colored since the R is dominant!

    Next: We’ll cross the F1 generation (the Rr) with the pure bred parents, to keep it simple, we’ll put the F1 generation on the top of the Punnet square and the parent on the left (although you can reverse these, it doesn’t matter)

    The pure bred dominant (RR)

    R r
    R RR Rr
    R RR Rr

    So here, you have two possible genotypes: RR and Rr, both will have the same phenotype.

    The pure bred recessive (rr)

    R r
    r Rr rr
    r Rr rr

    You see that when you cross the F1 with the recessive pure bred, you get two possible genotypes: Rr and rr, but now you have two phenotypes: rose and single comb.

    Hope this helps!
    References :

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