Explain
What is the principle of segregation and how is this demonstrated in the results of Mendel's monohybrid crosses?
The principle of segregation, also known as Mendel's first law, states that during the formation of gametes (sperm or eggs), the traits encoded by paired genes separate, so that each gamete receives only one copy of each gene. This results in offspring receiving one copy of each gene from each parent.
In Mendel's monohybrid crosses, he studied the inheritance of a single trait, such as flower color. He performed these experiments by crossing two purebred plants with different traits (e.g., one plant with white flowers and one plant with purple flowers). These plants are called the parental generation (P generation). By crossing the P generation plants, Mendel observed the first generation of offspring, known as the F1 generation.
In the F1 generation, Mendel found that all the offspring had the same trait (in this case, purple flowers), which indicated that a dominant trait was expressed and masked the recessive trait. However, when he allowed the F1 generation plants to self-fertilize or cross-pollinate with each other, he observed the second generation of offspring, the F2 generation.
In the F2 generation, Mendel observed a 3:1 ratio of dominant to recessive traits. This result demonstrated the principle of segregation, as it showed that the recessive trait (in this case, white flowers) reappeared in a ratio of about 25% of the offspring. This ratio is consistent with the idea that each plant possesses two copies of the gene for flower color (one inherited from each parent), and during gamete formation, these genes segregate randomly so that each offspring has an equal chance of inheriting a dominant or recessive copy.
Mendel's monohybrid crosses thus demonstrated the principle of segregation by showing that genes separate and maintain their independence during the formation of gametes, which results in the appearance of both dominant and recessive traits in the offspring.