Which Mendelian principle explains that the two alleles for a gene separate during gamete formation?

• A. Law of Independent Assortment
• B. Law of Segregation
• C. Law of Dominance
• D. Law of Crossing Over

Answer: (B)

The fundamental idea being tested is that the two alleles for a single gene separate when gametes are formed, so each gamete receives only one allele. This occurs during meiosis as homologous chromosomes segregate into different gametes, ensuring one allele from each pair ends up in a gamete and fertilization can restore the pair in the offspring. This is Mendel's Law of Segregation, describing how allele pairs separate and recombine randomly in offspring. The other principles don’t capture this specific separation: independent assortment talks about how different genes sort independently, not the two alleles of one gene; dominance explains how alleles are expressed in the phenotype, not how they segregate; and crossing over involves exchanging chromosome segments and creating new allele combinations, but it doesn’t describe the basic separation of alleles into gametes.