Gregor Mendel was a 19th century Moravian monk who demonstrated that the inheritance of traits (i.e. genes) follow particular laws:
- Law of Segregation: Each hereditary characteristic is controlled by two alleles which separate into different gametes
- Law of Independent Assortment: The separation of alleles for one gene is independent to allele separation for another gene
- Principle of Dominance: In pairs of alleles that are different, one allele will mask the effect of the other allele
These ‘laws’ are now known to be due to key events that occur during meiotic division:
- The law of segregation describes how homologous chromosomes (and hence allele pairs) are separated in meiosis I
- The law of independent assortment describes how homologous pairs align randomly (as bivalents) during metaphase I
Through the elucidation of the process of meiosis, we now know that there are certain exceptions to Mendel’s laws:
- Genes that are on the same chromosome (linked genes) will not undergo independent assortment (unless recombination occurs)
- Not all genes display a dominance hierarchy – certain traits may display codominance or incomplete dominance
The Role of Meiosis in Mendelian Inheritance
