Mendel, Genes, and Inheritance

Mendel, Genes, and Inheritance
Chapter 12

Why It Matters
 Red blood cells in sickle-cell disease

One amino acid in the wrong position causes the disease

12.1 The Beginnings of Genetics: Mendel’s Garden Peas
 Mendel chose true-breeding garden peas for his experiments  Mendel first worked with single-character crosses  Mendel’s single-character crosses led him to propose the principle of segregation  Mendel could predict both classes and proportions of offspring from his hypotheses

12.1 (cont.)
 Mendel used a testcross to check the validity of his hypotheses  Mendel tested the independence of different genes in crosses  Mendel’s research founded the field of genetics  Sutton’s chromosome theory of inheritance related Mendel’s genes to chromosomes

Blending Theory of Inheritance
 Popular belief until about 1900
• Hereditary traits blend evenly in offspring through mixing of parents’ blood

 Does not explain some observations:
• Extremes do not gradually disappear • Offspring sometimes have different traits than either parent

Gregor Mendel
 Founder/Father of genetics  Austrian monk (18221884)  First to use scientific method to study inheritance

Pea Experiments
 Garden pea (Pisum sativum)
• Easy to grow • Clearly defined characters or traits • True-breeding varieties
• Self-fertilized plants (same trait each generation)

• Easy to cross
• Cross-pollination between parents

Garden Pea

Animation: Crossing garden pea plants

Pea Characters

Single-Character Crosses
 P generation (Parents)
• Each pea produced contains an embryo

 F1 generation (Filial)
• First generation

 F2 generation
• Second generation

Flower Color Cross
 P generation
• Purple flowers crossed with white flowers

 F1 generation
• All F1 seeds formed purple flowers • Purple flower offspring crossed

 F2 generation
• Purple flowers (75%) • White flowers reappeared (25%)

Mendel’s First Hypothesis

 Genes