Learning Goal 1 The Work of Gregor Mendel Background on Gregor Mendel Details - Reasons for Choosing Peas - Mendel’s Experimental Design His Pea Experiment - Mendel’s Results - Mendel’s Laws Law of Dominance - Law of Segregation - Law of Independent Assortment - Genetic Terms Alleles - Homozygous - Heterozygous - Genotype - Phenotype -

Unit IV Learning Goal 1 Describe the research of Gregor Mendel and predict the outcome of genetic crosses.

Background on Gregor Mendel Details Austrian monk with an interest in gardening and a good knowledge of mathematics. In the 1840’s he experimented with the traits of garden peas (Pisum sativum).

Reasons for Choosing the Garden Pea Many varieties exist. Easy to observe contrasting traits. They self-pollinate. They reproduce quickly.

Mendel’s Experimental Design His Pea Experiment He allowed each variety to self-pollinate for several generations to ensure that they were true-breeding (offspring always exhibited the same trait). He called this the P 1 (parent) Generation. He took two of these parent plants with contrasting forms of the same trait and cross- pollinated them. The plants that resulted from this cross were called the F 1 Generation. Mendel then allowed the F 1 plants to self-pollinate to produce the F 2 Generation.

Mendel’s Results For every trait, one form would disappear from the F 1 generation. The disappearing trait reappeared in the ¼ of the F 2 generation. This was true of all seven traits that Mendel looked at. He used the term dominant to refer to the form of the trait exhibited in the F 1 generation and recessive to refer to the disappearing trait.

Mendel’s Laws Law of Dominance – One form of each trait is dominant and one is recessive.

Law of Segregation Members of each gene pair (alleles) separate during gamete formation (meiosis).

Law of Independent Assortment The genes for different traits separate independently from one another during gamete formation.

Genetic Terms Alleles – members of a gene pair symbolized by letters. Dominant alleles are capital letters, and recessive alleles are lower case. Homozygous – the alleles of a gene pair are identical (RR or rr). Heterozygous – the alleles of a gene pair are different (Rr). Genotype – describes the types of alleles of a gene pair Phenotype – describes the expression of the trait in the appearance.