Final answer:
The phenotype of offspring for a maternal effect trait is determined by the mother's genotype. In Mendelian inheritance and monohybrid crosses, phenotypic ratios follow Mendel's laws, but maternal effect traits bypass these and reflect the mother's genes alone, including those in mitochondrial DNA.
Step-by-step explanation:
For a maternal effect trait, the phenotype of all offspring is determined by the genotype of the mother. This is distinct from most trait inheritance where both parents contribute to the offspring's traits. In the context of the product rule, the probability of two independent events occurring simultaneously can be calculated by multiplying the individual probabilities of each event occurring alone. This rule, however, does not apply to maternal effect traits since the phenotype is exclusively determined by the mother's genes.
When Mendel performed monohybrid crosses, he noticed that all the F1 offspring exhibited the traits of one parent and the resulting F2 offspring displayed a 3:1 phenotypic ratio. This demonstrates a typical Mendelian inheritance pattern, and with large numbers of crosses, Mendel was able to calculate probabilities that fit his model of inheritance—predicting outcomes of other crosses. However, with maternal effect traits, the mother's genotype solely affects the offsprings' phenotypes, regardless of Mendelian inheritance patterns.
Moreover, it's important to note that some maternally inherited traits are encoded by mitochondrial DNA, which is exclusively inherited from the mother, such as mitochondria. This is a special case separate from nuclear DNA inheritance, and these traits would follow maternal inheritance patterns as well.