Final answer:
Mendel's classification had several limitations, such as incomplete dominance, linked genes, the influence of environmental factors, and a lack of knowledge about DNA and gene expression. These factors lead to deviations from the simple Mendelian inheritance patterns that Mendel described in his pea plant experiments.
Step-by-step explanation:
The limitations in Mendel's classification of inheritance patterns were related to his lack of knowledge about more complex genetic phenomena that were understood later. Specifically, these limitations included:
- Incomplete dominance - a form of inheritance where the phenotype of the heterozygote is somewhere between the phenotypes of the homozygotes, which Mendel did not observe in his pea plants.
- Linked genes - Mendel did not know about gene linkage and assumed that all genes assort independently, which is not the case when genes are located close together on the same chromosome.
- Environmental factors - The relationship between the environment and phenotype was not considered by Mendel, as he did not realize that environmental conditions could influence the expression of genetic traits.
- Lack of knowledge about DNA - Mendel worked with phenotypes and deduced the existence of underlying factors (now known as genes) governing traits, but he did not know about DNA, chromosomes, or the mechanism of gene expression.
Modern genetics has expanded upon Mendel's foundational work to include not only simple dominant and recessive inheritance patterns but also more complex interactions such as codominance, multiple alleles, and epistasis.