If two parental organisms of genotype pp and PP were crossed, what percentage of F1 offspring would be homozygous recessive? (Assume simple Mendelian pattern of inheritance and unlinked alleles.)
Zero, all offspring would be Pp.
Do you know how to use a Punnett square?
http://en.wikipedia.org/wiki/Punnett_square
75
To determine the percentage of F1 offspring that would be homozygous recessive, we need to understand how the genotype of the parental organisms and the pattern of inheritance will affect the offspring.
In this case, the parental organisms have genotypes pp and PP. The lowercase 'p' represents the recessive allele, while the uppercase 'P' represents the dominant allele.
When two organisms with different genotypes are crossed, the resulting offspring show the dominant phenotype if they inherit at least one dominant allele. On the other hand, to exhibit the recessive phenotype, an organism must carry two copies of the recessive allele.
Since the parental organisms have the genotypes pp and PP, they would produce offspring that are all heterozygous (Pp) in terms of genotype. Heterozygous individuals have one dominant allele and one recessive allele, and the dominant allele masks the recessive allele, resulting in the dominant phenotype being expressed.
Therefore, none of the F1 offspring would be homozygous recessive (pp) in this scenario. All F1 offspring would carry one dominant allele (P) and one recessive allele (p).