In the case of complete linkage and no crossing over, what is the expected phenotypic ratio from a heterozygote and a homozygote?

In a genetic cross involving complete linkage and no crossing over, the expected phenotypic ratio from a heterozygous individual crossed with a homozygous individual depends on the arrangement of alleles. When a heterozygote (for example, AaBb) is crossed with a homozygote (AABB), all offspring will inherit one complete set of linked alleles from the heterozygote and one complete set from the homozygote. This results in the offspring displaying the dominant phenotype associated with the dominant alleles from the homozygous parent.

Under these specific conditions, the phenotypic ratio that arises is 1:1. This means that half of the offspring will show the dominant phenotype and the other half will show the recessive phenotype, but because the genes are completely linked and no crossing over occurs, the offspring will not exhibit any recombinant types. Thus, the expected outcome will show only the parental phenotypes in equal proportions, aligning perfectly with a 1:1 ratio.

This understanding is crucial when dealing with linked genes, as it highlights the deviation from typical Mendelian ratios due to linkage and the absence of crossing over.