Long Answer
Hard difficulty • Structured explanation
Question 1
Long FormAnalyse how Mendel's experimental design ensured the validity and reliability of his results, and explain the three laws he proposed based on his findings.
- Mendel used true-breeding pea plants as parents, ensuring homozygosity and eliminating pre-existing genetic variation. His large sample sizes gave statistical credibility, and confirmation across successive generations proved his results reflected general rules rather than chance.
- Law of Dominance: In a pair of dissimilar alleles, one (dominant) is expressed in F1 while the other (recessive) is masked. This explains why all F1 plants in a monohybrid cross resemble one parent.
- Law of Segregation: Alleles of a gene pair segregate randomly during gamete formation so that each gamete carries only one allele. This explains the 3:1 phenotypic ratio and the 1:2:1 genotypic ratio at F2.
- Law of Independent Assortment: When two or more gene pairs are crossed, the segregation of one pair is independent of the other. This produces a 9:3:3:1 phenotypic ratio in F2 of a dihybrid cross.
- Mendel's use of mathematical logic to explain biological data and his analysis across multiple generations transformed genetics into a quantitative science, establishing the conceptual foundation for all subsequent developments in heredity.