Molecular Genetics

Genetic characters segregate independently.

Facts

• The ability of pea plants to produce round seeds (R) is dominant over the production of wrinkled (r) seed.
• When homozygous tall plants that produce round seeds (TR) are crossed with short plants that produce wrinkled seeds (tr) and the progeny (F1) are self-fertilized, the F2 generation has the following phenotypic distibution of individuals: TR: Tr: tR: tr:: 9: 3: 3: 1.
• Put another way, regardless of whether plants are tall or short, there are 3 producing round seeds for every one producing wrinkled seeds. Similarly, regardless of whether the plants produce round or wrinkled seeds, there are 3 tall plants for every short plant.

Interpretations

• These genetic characters assort independently of one another.
• The independent assortment of genetic characters is Mendel's 2nd Law.
• Today, characters that assort independently are called unlinked characters.

Further information

• Mendel did a similar experiment with seed color and seed shape traits (image from media-2.web.britannica.com)
• Mendel's crossing of plants differing in two characters is an example of a dihybrid cross.
• Another view of law of independent assortment.
• Some characters do not assort independently. They are called linked characters.
• Segregation of characters in the F2 generation can be used to map multiple genetic traits if the original cross was made between homozygotes differing at many loci.