Question

Two organisms, with genotypes BbDDand BBDd, are mated. Assuming independent assortment of the B/band D/dgenes, write the genotypes of all possible offspring from this cross and use the rules of probability to calculate the chance of each genotype occurring.

Short answer

Both organisms are heterozygous for one gene. The individual containing genotype BbDD will produce gametes having genotype BD and bD, while the individual containing BBDD will produce gametes having genotype BD and Bd.

After the fusion of these gametes, genotypes of the offspring will be BBDD, BBDd, BbDd, BbDD. According to the rule of probability, the chance of probability of all genotypes obtained will be 25 percent.

Step-by-step solution

Independent assortment:

Independent assortment is the principle given by John Gregor Mendel that states that different genes on the chromosomes assort or separate independently to the gametes when reproduction occurs.

It was discovered during the dihybrid cross in pea plants. It occurs during meiosis when homologous chromosomes separate and are distributed in daughter cells.

Step 2: Rule of the probability

Probability rules explain about chances of occurrence of a specific event in the total number of opportunities of the event. It was used by Mendel in his observations in monohybrid and dihybrid crosses in pea plants.

For example, in a genetic event of the production of round seeded pea plants in the F1 generation, the probability was 50 percent. However, in the F2 generation, it was 75 percent.

Step 3: Genotypes of all possible offspring from the cross between BbDD and BBDd:

Both are heterozygous for one gene, so the number of gametes produced by both parents will be 2n, where n is the number of traits having heterozygosity. BbDD will produce gametes having BD and bD genotypes. BBDd will produce gametes having genotypes BD and Bd.

So after cross-fertilization, offspring produced will be having genotypes: BBDD, BBDd, BbDD, BbDd.

All possible genotypes in offspring will have one probability in four possible genotypes, which means there is a 25 percent probability of having all possible genotypes in offspring.