Mendel's experiments — A/L Biology

What must I remember about Mendel's experiments?

• Gregor Mendel established classical genetics using true-breeding garden pea plants (Pisum sativum) studying seven discrete pairs of contrasting traits.
• Mendel's First Law (Law of Segregation): Alleles of a gene segregate during gamete formation so that each gamete carries only one allele for each gene.
• Monohybrid cross ratios: Crossing two heterozygous individuals (F1: Tt × Tt) produces a phenotypic ratio of 3:1 (dominant:recessive) and genotypic ratio of 1:2:1 (TT:Tt:tt).
• Mendel's Second Law (Law of Independent Assortment): Alleles of two or more different genes assort independently of each other into gametes during meiosis (valid for unlinked genes on different chromosomes).
• Dihybrid cross phenotypic ratio: Crossing dihybrids (RrYy × RrYy) yields a classic 9:3:3:1 phenotypic distribution in the F2 generation.

Test yourself (1 minute)

1. Test cross principle

   Crossing an individual showing a dominant phenotype with a homozygous recessive individual (e.g., T_ × tt) to determine whether the dominant genotype is homozygous (TT) or heterozygous (Tt).

2. Punnett square construction

   Always show parental genotypes, gamete types in circles, and clear offspring genotype/phenotype distinctions to earn full structured essay marks.

3. Reasons for Mendel's success

   Pisum sativum was self-pollinating, easy to cultivate, had short generation times, and exhibited clear, non-overlapping contrasting traits.

Practise Mendel's experiments questions today

Source: NIE G.C.E. (A/L) Biology Syllabus & Resource Book, Unit 6

What comes next?

Next in the syllabus

Where does Mendel's experiments fit in the syllabus?

Year 1 · Term 2