Final answer:
In pedigree analysis, the genotypes are determined by the pattern of inheritance shown. For a mating between two heterozygous individuals for a recessive lethal allele, the expected surviving offspring genotypic ratio would be 1:2:0. A cross between a homozygous recessive dwarf pea plant and a heterozygous tall pea plant would yield a 1:1 phenotypic ratio of tall to dwarf plants.
Step-by-step explanation:
Understanding Pedigrees and Genetic Ratios
Genotypes in traditional pedigree analysis are denoted by letters where a dominant allele is represented by 'A' and a recessive allele by 'a'. A homozygous dominant individual has the genotype 'AA', a heterozygous individual 'Aa', and a homozygous recessive 'aa'. In a pedigree where the genotypes of individuals labeled are 1-aa, 2-AA, 3-AA, individuals 1 is homozygous recessive, while individuals 2 and 3 are homozygous dominant.
When two heterozygous individuals mate, with a recessive lethal allele that expresses in utero, genotypic ratios can be affected since the homozygous recessive genotype might not survive to birth. Typically, the genotypic ratio would be 1:2:1 (homozygous dominant:heterozygous:homozygous recessive), but with a lethal allele, the homozygous recessive individuals would not appear in the phenotype, altering the expected ratio.
Considering a cross between a dwarf pea plant (homozygous recessive) and a tall pea plant (heterozygous), the phenotypic ratio of the offspring will be 1:1 (tall to dwarf) since the dwarf plant can only contribute a recessive allele and the tall plant can contribute a dominant or a recessive allele, so each offspring has a 50% chance of being tall.
A human male cannot be a carrier of red-green color blindness; as it is a sex-linked condition, a male will either have the condition or not since the gene for color blindness is located on the X chromosome and males only have one X chromosome.
An allele is a form of a gene present at a particular locus on a chromosome. The recessive allele affects the phenotype only in the homozygous condition, whereas a dominant allele can affect the phenotype in both homozygous and heterozygous conditions. It's not always true that individuals with the same phenotype share the same genotype, as a heterozygous individual can exhibit a dominant phenotype.
For the tetrahybrid cross question, the expected proportion of offspring with a dominant phenotype at all four loci is calculated through probabilities. The genotype proportion that results in a dominant phenotype can be homozygous dominant or heterozygous at each locus and using the sum rule and product rule, the cumulative proportion is 81/256.