Final answer:
When crossing a female with genotype rrAa and a male with genotype RRaa, all the offspring will have one dominant R allele and at least one recessive a allele. The offspring genotypes will be either RrAa or Rraa, leading to phenotypic ratios of 100% R phenotype and a 1:1 ratio for the A:a phenotypes, depending on which trait is visible or measurable in the organism.
Step-by-step explanation:
The question asks about the proportions of offspring for a cross between two individuals, one with genotype rrAa and the other with genotype RRaa. This is a classic Mendelian genetics problem that involves predicting the phenotypic and genotypic ratios of the offspring when two individuals mate. It involves understanding how the laws of segregation and independent assortment apply to the alleles for two separate genes
The cross between rrAa (female) and RRaa (male) will result in all offspring carrying at least one R allele since R is dominant and the male is homozygous for it (RR). All offspring will also carry at least one a allele because both parents carry the recessive a allele. Therefore, the offspring will have the following genotypic ratio: RrAa and Rraa. The offspring cannot possess the genotype rr since there is no rr allele coming from the male.
As for the A and a alleles, since the female provides either A or a and the male only provides a recessive a allele, the offspring have a 50% chance of being Aa and a 50% chance of being aa. This results in two possible genotype combinations for the offspring: 50% RrAa and 50% Rraa. If we look at phenotypic ratios, all offspring will be R- which is the dominant phenotype, thus 100% of the offspring will exhibit the dominant R phenotype, while for the A and a alleles, since A is dominant over a, neither phenotype will be visible in the case of aa genotype. Therefore, 50% of the offspring would express the A phenotype while the other 50% would express the a phenotype. However, the actual visible traits would depend on what the R, A, and a alleles code for in terms of the organism's physical characteristics.