Final answer:
Expected Progeny Differences (EPD) predict genetic contribution to offspring's traits, and deviations from expected ratios, such as 9:3:3:1 in dihybrid crosses, can be due to linkage or gene interactions. Environmental conditions and sample size can also affect observed outcomes.
Step-by-step explanation:
Expected Progeny Differences (EPD) account for the genetic differences in offspring based on parental traits. EPDs are especially useful in animal breeding and agriculture for predicting the performance of future progeny. They take into account the heritability of traits and the average effect of allelic substitutions, providing a quantitative measure of an animal's genetic contribution to its offspring for specific traits.
When it comes to a dihybrid cross, the expected phenotypic ratio is 9:3:3:1. This ratio sometimes deviates from the expectation due to various reasons, such as linkage of genes, which can occur when alleles do not assort independently because they are located on the same chromosome. In such cases, the expected Mendelian dihybrid ratio is not observed.
In the shepherd's-purse plant example, the observed ratio might differ from the expected dihybrid 9:3:3:1 ratio if the alleles for the traits are linked or if there are interactions between genes (epistasis). Such deviations suggest that the inheritance of traits in this plant does not follow simple Mendelian genetics.
If far fewer plants were used, the results could display more variance due to genetic drift and sampling error. Factors like extreme environmental conditions, such as strong winds, could introduce experimental error by affecting the actual pollination or survival of the plants in unpredictable ways, thereby altering the expected ratios.