New combinations of characters in the F2 progeny arise primarily due to Mendel’s Law of Independent Assortment and the Law of Purity of Gametes. Independent assortment ensures that alleles for different traits segregate independently during gamete formation, leading to various combinations. The law of purity of gametes states that each gamete contains only one allele for each trait, contributing to the diverse combinations in the F2 generation.
Here’s a more detailed explanation:
Independent Assortment:
When considering two or more traits, the alleles for each trait separate independently during the formation of gametes (sperm or egg cells). For example, if a plant inherits alleles for both round/wrinkled seeds and yellow/green seeds, these alleles don’t necessarily have to remain together in the same gamete. They can segregate independently, leading to combinations like round-green and wrinkled-yellow, which might not be present in the parental generation.
Law of Purity of Gametes:
Each gamete, as it is being formed, carries only one allele for each trait. This ensures that when two gametes fuse during fertilization to form a zygote, the zygote will receive one allele from each parent for each trait, resulting in a new combination of traits in the F2 progeny.
Resulting Combinations:
These mechanisms lead to new combinations of traits in the F2 generation. For instance, if you cross a plant with round, yellow seeds (RRYY) with a plant with wrinkled, green seeds (rryy), the F1 generation will all have round, yellow seeds (RrYy). However, when these F1 plants are crossed, you can get combinations like round, green (RrYy) and wrinkled, yellow (rrYy), which were not present in the parental generation.