mendelian

Mendelian refers to the principles of heredity first described by Gregor Mendel in the 19th century, based on experiments with pea plants. Mendel proposed that traits are controlled by discrete heritable units that come in alternative forms called alleles. When organisms reproduce, they pass one allele for each trait to their offspring, leading to predictable patterns of inheritance.

Central to Mendelian genetics are two core laws. The law of segregation states that allele pairs separate during gamete formation, so offspring inherit one allele from each parent. The law of independent assortment holds that the alleles of different genes assort independently during gamete formation, provided the genes are on different chromosomes or far apart on the same chromosome. These ideas explain how genetic variation arises and how certain trait combinations occur with expected frequencies, often modeled with Punnett squares.

Mendelian inheritance also highlights dominant and recessive relationships, where a dominant allele can mask the expression of a recessive one in the phenotype. However, many traits do not follow simple Mendelian patterns. Incomplete dominance, codominance, multiple alleles, polygenic inheritance, and gene linkage can produce deviations from the classic rules. Environmental factors and epigenetic effects can also influence phenotype.

In contemporary genetics, Mendelian patterns remain a foundational concept for single-gene (monogenic) traits and form part of a broader framework that includes chromosomal behavior, molecular biology, and probabilistic modelling. The term “Mendelian” is commonly used to describe inheritance that closely follows these simple, unit-allele patterns.