Final answer:
The probability of offspring being homozygous recessive (bb) when both parents are homozygous recessive (bb) is 100%, as each parent can only contribute a recessive b allele to the offspring.
Step-by-step explanation:
When two parents with homozygous recessive genotypes (bb) mate, the genetic outcome for their offspring is predetermined, as each parent can only contribute the recessive b allele. This scenario is a classic example of Mendelian inheritance, and the resulting genotype of the offspring will be homozygous recessive (bb).
The use of a Punnett square, a visual tool in genetics, reinforces the predictable outcome in this case. Each parent can only pass on the recessive b allele, and all combinations in the Punnett square yield offspring with the genotype bb. The squares of the Punnett square represent all possible combinations of alleles from both parents, and in this specific scenario, each square shows the offspring inheriting the recessive b allele from both parents.
The application of the sum and product rules for inheritance further elucidates the probability of the offspring having the genotype bb. In this case, the probability is calculated as 1 (from the mother) times 1 (from the father), which equals 1. The probability of the offspring having the genotype bb is therefore 1 (or 100%).
This high probability reflects the certainty associated with the genetic outcome when both parents are homozygous recessive. The simplicity of this scenario, where each parent contributes the same recessive allele, aligns with Mendel's laws of inheritance and provides a clear illustration of the principles governing genetic transmission in specific mating situations.