- The Law of Segregation assumes that each organism only has two copies of a gene. And for the majority of plants and animals this is correct. However, there are exceptions. The peas he worked with do, in fact, have 2 sets of chromosomes (this is known as being diploid, or a 2N organism). However, other nearby plants were not. Apples can have an odd number of chromosomes (3N). Tobacco is a tetraploid (4N). It was fortunate that Mendel didn’t turn his attention to these plants since their crosses can get more complicated.
- Secondly, we now know that the Law of Independent assortment is not an absolute rule. When Mendel was working he assumed that each gene was free-floating and totally free from any other gene. This is not correct. Genes are tied together through their sequences into large collections of proteins and DNA known as chromosomes. And while chromosomes can switch around their genes with neighboring sister chromosomes during sperm or egg development, genes that are too close can affect each other’s chances.
Mendel worked with seven visible traits when he looked at peas. Each one just happened to be on a different chromosome and free from any possible interference or linkage.
Saying that Gregor Johann Mendel was lucky in his work will be devaluation of his hard work and dedication. His experiments had a large sampling size, some 10000 Pea plants. This gives greater credibility to his data. Further, he was the first to use statistical analysis and mathematical logic in solving problems in biology.