Biology – Chapter 11 – Introduction to Genetics Section 1 – The work of Gregor Mendel

I. Genetics – the scientific study of the ways in which hereditary information is passed on from parents to offspring.

A. Gregor Mendel – Austrian monk that pioneered the scientific study of heredity.

1. Pea plants were the basis for Mendel’s studies a. 1857-1865 – Mendel investigated inheritance of certain traits in pea plants. b. Why pea plants?

1. They are easy to grow 2. They mature quickly. 3. Their traits are contrasting and easily seen 4. They have an enclosed structure of flower for self-pollination Pea plants are true breeding – if allowed to self pollinate, they produce offspring identical to

themselves Thus, Mendel could control their pollination.

B. Genes and Dominance

1. Trait – a specific characteristic that varies from one individual to another. 2. Mendel studied 7 contrasting traits:

1. White flower/purple flower 2. yellow pod/green pod 3. yellow seed/ green seed 4. round seed/ wrinkled seed 5. Short/ tall plants 6. Grey/white seed coat 7. Axial/ terminal flower position

C. Mendel’s Experiments

1. He named the original pair of plants in each trait study the parental generation; or “P” 2. Their offspring are the filial generation; or F1 3. Hybrid – offspring of crosses between pure parents with different traits 4. When Mendel did crosses between pure plants:

a. The offspring showed one contrasting trait – known as the dominant P1 generation pure tall x pure short F1 generation produces all tall plants

5. Mendel made two conclusions: a. Biological inheritance is determined by factors passed from one generation to the next.

1. Factors determining traits are called genes. 2. Alleles are different forms of a gene

b. Principle of Dominance - Some alleles are dominant and some are recessive. 1. Dominant alleles always show themselves 2. Recessive alleles exhibit that form ONLY when the dominant allele is not present.

D. Segregation

1. Alleles occur in pairs that are separated from each other during gamete (sex cell) formation 2. The alleles from one parent combine with the alleles of the other parent at fertilization 3. Each gamete carries one copy of each gene