*Mendel and the Gene Idea homework help*?

Question

I'm not asking for anyone to do it for me. I just need someone to expain it to me, but if you know what to do, by all means go right ahead.

You are handed a "mystery" pea plant with long stems and axial flowers, and asked to determine its genotype as quickly as possible. You know the allele for long stems (L) is dominant to that for dwarf stems (l) and that the allele for axial flowers (A) is dominant to that for terminal flowers (a).

1. What are all the possible genotypes for you mystery plant?

2. Describe the one cross you would do, out in your garden, to determine the exact genotype of your mystery plant.

3. While you are waiting for the results of your cross, you go back inside and sit at your desk. You make a seperate prediction of results for each possible genotype listed in part one. How do you do this?

Make these predictions, using the following format: "If the genotype of my mystery plant is _____, the plants resulting from cross will be____."

5. If one-half of your offspring plants have long stems with axial flowers and one-half have long systems with terminal flowers, what must be the genotype of your mystery plant?

6. Explain why the activities you peformed in parts 3 and 4 were not "doing a cross."

I know it's alot but I'm not asking anyone to do this. I just posted all of it so that you guys would know what I was talking about. I have an idea on how to do this, but I need someone elses view, you know what I mean. So any little explaination will do. Please Help.

Answer 1

1. The original plant could be LLAA, LlAA, LLAa or LlAa
2. I would do a "test cross" which is a cross of your plant with a completely recessive plant (llaa).

3. If your plant is LLAA, then all of the offspring will be LlAa and will have the same phenotype as your mystery parent.
If your plant is LlAA, then half will be LlAa and half will be llAa.

You can work out the other 2 possible sets of offspring from the different genotypes of original plants.

The test cross is used to determine the genotype of an individual.

Answer 2

Because the plant you have is long with axial flowers it has to have both the dominant alleles L and A. Therefore the possible phenotypes are LLAA, LlAa, LLAa, or LlAA. Crossing this plant with a full recessive (llaa) would be the test I would use. The possible results you can figure using a punnet square. If any of the offspring are recessive you know you have some hidden recessive alleles in the parent.

Answer 3

Go to this website and work through it. You need the punnett square for analysis. The genotype for a homozygote plant would be either LLAA or LlAa. Either genotype would produce a log plant with axial flowers. Now work the punnett squares with LLAA versus LLAA and LlAa versus LiAa and LLAA versus LlAa. remember, the gametes for each would be a mix of the length gene L and the flower gene A so a gamete in the punnet square would look like LA or La or lA or la.