Definition of recessive

The term "recessive" is commonly used in genetics to describe an allele (alternative form of a gene) that is less likely to be expressed when inherited. This term originated from the concept of dominant and recessive traits in genetics, which were first observed in pea plant breeding experiments conducted by Gregor Mendel in the 19th century. In Mendel's sister chromatid exchange experiment, he crossbred pea plants with different colored flowers (such as yellow and purple). He observed that the first generation (F1) always expressed the dominant trait (such as yellow), but the offspring of the F1 generation (F2) exhibited a more diverse range of phenotypes (observable characteristics). This phenomenon was later explained by the concept of genetic segregation, where the parent's dominant trait hid the recessive allele, but in the F2 generation, the recessive allele was expressed due to the law of segregation. The term "recessive" comes from the idea that the expression of this allele is 'recessive' and requires two copies of the gene (one from each parent) to be expressed. In contrast, the "dominant" allele only requires a single copy to be expressed. This concept explains why certain recessive traits, such as brown eyes or curly hair, may be less observed in certain populations because they require both parents to carry the recessive allele. In summary, "recessive" is a term used in genetics to describe an allele that is less likely to be expressed when inherited, and its origin can be traced back to the late 19th century and the experiments conducted by Gregor Mendel.