THE ORIGINS OF GENETICS Genetics – the branch of biology that focuses on heredity Heredity – the passing of traits from parents to offspring Traits – characteristics such as eye color, hair color, height

Gregor Mendel An Austrian monk who carried out experiments in which he bred different varieties of the garden pea. He was the first to develop rules that accurately predict patterns of heredity. He used peas because (1) several traits existed in two clearly different forms, (2) you could control mating, and (3) the garden pea is small, grows easily, matures quickly, and produces many offspring.

Seven Pea Characteristics

Three Steps of Mendel’s Experiment: 1. Mendel allowed each variety of garden peas to self-pollinate for several generations to produce a true-breeding parental generation or P generation. 2. Mendel then cross-pollinated two P generation plants that had contrasting forms of a trait, such as purple flowers and white flowers. The offspring were the first filial generation or F1 generation. 3. Finally, Mendel allowed the F1 generation to self-pollinate. The offspring of the F1 generation plants were called the second filial generation or F2 generation. (Fig. 3)

Ratio 3:1

Mendel’s Results F1 plants – showed only one form of the trait; the other trait disappeared F2 plants – the missing trait reappeared *For each of the seven traits Mendel studied, he found a 3:1 ratio of plants expressing the contrasting traits in the F2 generation

Genes – pieces of DNA that code for a particular character or trait MENDEL’S THEORY Genes – pieces of DNA that code for a particular character or trait

Mendel’s Theory of Heredity: 1. For each inherited trait, an individual has two copies of the gene – one from each parent. 2. There are alternative versions of these genes – the different versions of the gene are called alleles. 3. When two different alleles occur together, one of them may be completely expressed, while the other may have no observable effect on the organisms appearance. dominant – the expressed form of a trait recessive – the trait not expressed, unless two are present

4. When gametes are formed, the alleles for each gene in an individual separate independently of one another. Thus, gametes carry only one allele for each inherited trait. When gametes unite during fertilization, each gamete contributes one allele.

The Laws of Heredity: 1. Law of Segregation – states that the two alleles for a character or trait segregate (separate) when gametes are formed 2. Law of Independent Assortment - states genes for different traits are sorted separately from one another so that the inheritance of one trait is not dependent on the inheritance of another 3. Law of Dominance – states an organism with alternate forms of a gene will express the form that is dominant.

More Vocabulary: homozygous – the two alleles of a particular gene are the same ex: PP or pp heterozygous – the two alleles of a particular gene are different ex: Pp genotype – the set of alleles (genes) for a trait ex: PP, Pp, pp phenotype - the physical appearance of a trait ex: purple flower, white flower