Final answer:
The offspring produced by one parent with BB genotype and the other with Bg genotype has a 75% chance of having brown eyes. This is due to the dominance of the B allele and the possible genetic combinations revealed by using a Punnett square.
Step-by-step explanation:
The possibility that the offspring produced will have brown eyes, given one parent with genotype BB and the other Bg, is 75%.
The explanation for this is based on classic Mendelian genetics and the use of a Punnett square. The parent with genotype BB can only contribute a B allele to the offspring, whereas the parent with genotype Bg can contribute either a B or a g allele with equal probability. When you create a Punnett square for this cross, you find that there are four possible combinations of alleles in the offspring: BB, BB, Bg, Bg. Out of these combinations, three (BB, BB, Bg) result in a brown-eyed phenotype, as the B allele is dominant over the g allele. Thus, the probability of the offspring having brown eyes is 3 out of 4, or 75%.
Regarding the student's question about how two brown-eyed parents can produce a green-eyed child, the correct answer is that both parents are heterozygous, having the green trait on the green-blue eye gene. This means both parents have one dominant brown allele and one recessive green allele (Bb). The Punnett square model would predict a 25% chance of the offspring being homozygous recessive (bb) and thus having green eyes, which is genetically possible.