Final answer:
Mendel's law of segregation describes that paired unit factors, or genes, segregate equally into gametes, ensuring each gamete receives one allele with equal likelihood.
Step-by-step explanation:
Mendel's law of segregation states that during the formation of gametes, the paired unit factors (that is, genes) segregate independently so that each gamete receives one or the other with equal likelihood. This fundamental genetic principle means that every possible combination of alleles is equally likely to occur. The expression 'segregate independently' refers to the fact that each allele for a gene ends up in a different gamete during the process of meiosis, which is the division of sex cells. This ensures that offspring have an equal chance of inheriting any combination of parental factors. For example, if a pea plant has one allele for yellow seeds and one for green seeds, each gamete (egg or sperm) produced by that plant will carry only one of these alleles.
Moreover, Mendel observed that true-breeding pea plants with contrasting traits could produce offspring that might express either trait. The principle underlying this is that alleles can be either dominant or recessive. Heterozygous genotypes arise when an offspring inherits different alleles from each parent, leading to a blend of traits that may result in the dominant trait being expressed. Thus, Mendel demonstrated that traits are not blended in the offspring, but instead, inherited as discrete units.