Final answer:
The expected phenotypic ratio for a mating between two heterozygous individuals for a recessive lethal allele is 1:2:0 for the surviving offspring because the homozygous recessive individuals will not survive to be observed.
Step-by-step explanation:
The question asked pertains to predicting the expected phenotypic ratios from genetic crosses between parents with specific genotypes. When dealing with simple Mendelian inheritance, typical ratios such as 3:1 or 9:3:3:1 can be expected for monohybrid and dihybrid crosses, respectively. However, when a mating occurs between two individuals heterozygous for a recessive lethal allele, the phenotypic ratio for surviving offspring deviates from Mendel's expected ratios due to the non-viability of homozygous recessive individuals.
For a mating between two individuals that are heterozygous for a recessive lethal allele that is expressed in utero (Aa x Aa), the expected genotypic ratio would be 2:1 for the surviving offspring, since the homozygous recessive (aa) genotype would not be viable, and there would be no homozygous recessive individuals alive to express the phenotype. Thus, the correct genotypic ratio is 1:2:0, when considering only the surviving offspring, which also reflects the phenotypic ratio as there would be no phenotypic expression of the recessive lethal allele in the population. This results in a presence of only the dominant phenotype (represented as 'A') and the heterozygous phenotype (represented as 'Aa').