Question

1. Define test cross Answer

2. You mate two organisms one with a dominant phenotype and one with a recessive phenotype. For which organism are you sure of the genotype and for which are you unsure of the genotype. Explain your answers. Answer

3. A geneticist crosses a green pea plant with a yellow pea plant and all the offspring are yellow. He accidentally mixes the seeds.

a. What is the dominant phenotype and which is the recessive phenotype Answer

What test can he do to figure out what seeds are homozygous and what seeds are heterozygous? Answer

b. Write down the phenotypes of the cross Answer

c. Write down the possible genotypes of the cross Answer b.

4. Brown fur in rabbits is dominant to white fur - do not give letters use either homozygous or heterozygous. a. If you cross a brown rabbit with a white rabbit and all the offspring are brown then the parent with the unknown genotype must be Answer b. If you cross a brown rabbit with a white rabbit and some of the offspring are brown then the parent with the unknown genotype must be Answer

Answer 1

1) A test cross is a cross which is used to test the genotype of an individual/organism by crossing it with a known homozygous recessive type.

2) The genotype of an organism with a recessive phenotype is sure because there is only one case in the cross which is homozygous recessive (aa). Whereas, the genotype of an organism with dominant phenotype is unsure as it can be by both homozygous dominant (AA) and heterozygous (Aa).

3-a) Yellow pea plant is the dominant phenotype and green pea plant is the recessive as the cross between yellow and green pea plants leads to the production of only yellow pea plants and no green pea plants.

AA/aa	a
A	Aa (yellow pea plant)

He can do a test cross in order to find out what seeds are homozygous and what seeds are heterozygous. If we cross the homozygous dominant with the homozygous recessive, then all the offspring will be heterozygous dominant. But if we cross a heterozygous with a homozygous recessive, then 50% will be heterozygous dominant and 50% will homozygous recessive.

b) The phenotype of the cross will be:-

Yellow pea plant X Green pea plant

c) The genotypes of the cross will be:-

Homozygous dominant (AA) X Homozygous recessive (aa)

4) The parent with unknown genotype will be homozygous because cross between the unknown and recessive type produces 100% dominant type and 0% percent recessive type as the homozygous does not provide recessive allele to the cross.

If cross between a brown rabbit and a white rabbit produces some of the offspring are brown then the parent with the unknown genotype must be Heterozygous because this cross will produce 50% dominant type (brown) and 50% recessive type (white) as heterozygous provides recessive allele to the cross.