Monohybrid problems and the dihybrid cross

Order for solving a genetics problem: 1) mark traits with letters (dominant — capital, recessive — lower case); 2) write the parents’ genotypes (a recessive phenotype is always aa; a dominant phenotype A_ is AA or Aa); 3) write each parent’s gametes (a heterozygote gives two kinds, a homozygote one kind); 4) combine gametes in a Punnett square to find the offspring genotypes; 5) write the genotype and phenotype ratios and answer the question. If a recessive individual appears among the offspring, both parents carry at least one recessive allele (a). The expected ratios are probabilities: in a small number of offspring the real result can differ a little from the ratio. Keep the records tidy: P, G, F1, F2.