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What is the probability distribution of offspring genotypes resulting from a cross between two parents with specific genotypes?

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To determine the probability distribution of offspring genotypes resulting from a cross between two parents, we typically use a Punnett square. The specific genotypes of the parents will dictate the possible combinations of alleles in their offspring.

Let's use a general example to illustrate how to do this:

Example Cross

Assume we have two parents with the following genotypes:

  • Parent 1: Aa (heterozygous)
  • Parent 2: Aa (heterozygous)

Step 1: Determine Alleles

Each parent can contribute one of two alleles (A or a). If we label the alleles as follows:

  • A = dominant allele
  • a = recessive allele

Step 2: Set Up a Punnett Square

The Punnett square for this cross would look like this:

         A      a
      ----------------
   A |   AA   |  Aa   |
      ----------------
   a |   Aa   |  aa   |
      ----------------

Step 3: Determine Offspring Genotypes

From the Punnett square, we can see the possible genotypes of the offspring:

  1. AA (homozygous dominant)
  2. Aa (heterozygous)
  3. Aa (heterozygous)
  4. aa (homozygous recessive)

Step 4: Calculate Probabilities

Now, we count the occurrences of each genotype:

  • AA: 1
  • Aa: 2
  • aa: 1

Total offspring = 4

So, the probabilities for each genotype are:

  • P(AA) = 1/4 = 0.25
  • P(Aa) = 2/4 = 0.50
  • P(aa) = 1/4 = 0.25

Conclusion

In this example, the probability distribution of offspring genotypes from a cross between two heterozygous parents (Aa x Aa) is:

  • 25% AA
  • 50% Aa
  • 25% aa

General Method

You can use the same method for any parental genotype combinations by adjusting the alleles accordingly and constructing a Punnett square to find the ratios of the possible genotypes.