Final answer:
Alleles for different genes are often inherited together due to linkage, which occurs when alleles are located close on the same chromosome and are passed down as a unit, affecting inherited trait combinations and the expected Mendelian ratios.
Step-by-step explanation:
Sometimes alleles for different genes are inherited together due to the linkage phenomenon, where alleles located in close proximity on the same chromosome are more likely to be inherited together. This occurs because genes that are close to each other on a chromosome have a lower probability of being separated by crossover events during meiosis. Therefore, these linked genes tend to be transmitted as a unit, resulting in the inheritance of specific combinations of traits, like certain eye colors with certain hair colors. Multiple alleles, like those for ABO blood type, with alleles IA, IB, and i, increase the genetic diversity in populations.
Linkage can disrupt the expected Mendelian ratios as seen in a Punnett square, especially in a dihybrid cross. For example, if genes for flower color and plant height were next to each other on a chromosome, the classical 9:3:3:1 outcome would not apply. Instead, the offspring would more likely exhibit the parental genotypes. Geneticists use the proportion of recombinant gametes to create linkage maps to determine the relative positions of genes on a chromosome.