Final answer:
The expected ratio of phenotypes for offspring from a cross between homozygous recessive and heterozygote individuals, assuming complete dominance, is 1:1. With a tetrahybrid cross, the probability of offspring having the dominant phenotype at all loci is 81/256. For a single gene cross, involving a pea plant's height, the resulting phenotypic ratio using a Punnett square is also 1:1.
Step-by-step explanation:
Explanation of Phenotypic Ratio From Crosses
When considering a cross between a homozygous recessive individual and a heterozygote, the expected ratio of phenotypes in their offspring, assuming complete dominance, would be 1:1. This means that half of the offspring will display the dominant phenotype and half will display the recessive phenotype. If we use the letters 'A' and 'a' to denote the alleles, where 'A' is dominant and 'a' is recessive, the genotypic makeup of the offspring will be Aa and aa in equal proportions. The Aa individuals will express the dominant phenotype, while the aa individuals will express the recessive phenotype.
For a tetrahybrid cross where individuals differ at four loci, the expected proportion of offspring with the dominant phenotype at all loci can be calculated using genotypic proportions as described. The sum and product rules of probability apply. Each locus has a 3/4 chance of displaying the dominant phenotype (either homozygous dominant or heterozygous), and the combined probability across all four loci is 3/4 × 3/4 × 3/4 × 3/4, or 81/256. This calculation represents the proportion of offspring with the dominant phenotype for all four loci.
Regarding a Punnett square prediction for a cross between a homozygous recessive (dwarf) and a heterozygous (tall) pea plant, the phenotypic ratio is expected to be 1:1, similar to the first example discussed. The offspring will be either dwarf (recessive phenotype) or tall (dominant phenotype) in equal proportions as the heterozygote parent can pass on either the dominant or recessive allele.