Question

Which of the following correctly describes this cross? Choose all that apply.

Now determine the genotypes of the possible gametes and set up a Punnett square for the cross between two double heterozygotes, as you did before in a previous question (no need to attach that Punnett square). From your Punnett square, determine how many individual kernels have the genotypes and phenotypes shown in the table below. Enter your answers as a number (e.g. 7) not a word (e.g. seven)

X

Y

Z

W

In Mendel’s pea plants, the dominant flower color was purple, which we can indicate as P. The recessive color, white, can therefore be expressed as p. If you were given a random pea plant with purple flowers, how would you be able to tell if the plant was homozygous (PP) or heterozygous (Pp)? The answer lies in the fact that even though purple flowers can be PP or Pp, white flowers can only be pp. So the genotype of an individual expressing the recessive allele is always known. Determine the outcome of two crosses to a white flower: in one case hypothesize that the purple parent is homozygous, and in the other hypothesize that it is heterozygous.

Hypothesis 1: The purple parent is homozygous, PP. What would be the offspring's genotype and phenotype after a test cross between this parent and a homozygous recessive pp organism?

In Mendel’s pea plants, the dominant flower color was purple, which we can indicate as P. The recessive color, white, can therefore be expressed as p. If you were given a random pea plant with purple flowers, how would you be able to tell if the plant was homozygous (PP) or heterozygous (Pp)? The answer lies in the fact that even though purple flowers can be PP or Pp, white flowers can only be pp. So the genotype of an individual expressing the recessive allele is always known. On the Punnett squares below determine the outcome of two crosses to a white flower: in one case hypothesize that the purple parent is homozygous, and in the other hypothesize that it is heterozygous. Write the genotypes of the white parent along the top of the square and that of the purple parent along the side.

Hypothesis 2: The purple parent is heterozygous, Pp. If the test cross is between this parent and the homozygous recessive pp individual, what would be the genotype and phenotype of their offspring?

Answer 1

Answer:

If testcross ratio is 1:1 (purple : white), it means that the hybrid genotype would be Pp (heterozygous). See punnet square.

Pp (hybrid) x pp (white)---Testcross

	p
P	Pp (purple)
p	pp (white)

Phenotypic ratio = Purple (1) : White (1)

If testcross ratio produces only purple phenotype progeny, it means that the hybrid genotype would be PP (homozygous). See punnet square.

PP (hybrid) x pp (white)---Testcross

	p
P	Pp (purple)

Phenotypic ratio= All progeny are purple.