Text lesson

Unit 3 — Variation of Traits in Living Organisms

Science — Third Preparatory

1.4 Mendel and the discovery of the laws of heredity

In the nineteenth century the scientist Gregor Mendel (1822–1884) carried out systematic experiments on pea plants. Why peas?

They show clear, contrasting traits that are easy to tell apart: seed colour (yellow/green), seed shape (round/wrinkled), plant height (tall/short), flower colour (purple/white), flower position (axial/terminal), pod shape (inflated/constricted), pod colour (green/yellow).
Pollination can be controlled easily.

Mendel crossed (hybridised) plants that differ in one trait after making sure each parent was purebred (always gave the same trait).
Analysing his results he concluded that inherited traits do not appear at random but follow regular patterns that can be explained scientifically and used to predict the probability of traits in offspring.
This was the foundation of modern genetics.
Pairs of contrasting traits in pea plants (dominant / recessive):

Genetic notation→P = parents; ♂ = male; ♀ = female; × = cross; G = gametes; F₁ = first generation; F₂ = second generation.

Unit 3 — Variation of Traits in Living Organisms · 5 / 24

1.4 Mendel and the discovery of the laws of heredity