The Work of Gregor Mendel (Ch 11.1)

The Experiment Where do we get our characteristics from? Heredity: the inheritance of characteristics that have been passed on through generations Genetics: the scientific study of heredity Gregor Mendel  Father of Genetics Famous experiment  garden peas  known as “the model system” Model system Easy to study Can indicate how other organisms function

Garden Pea Experiment Plants have to reproduce by means of sexual reproduction How do we know they are reproducing sexually instead of asexually? Fertilization: male and female reproductive cells join together Pea plants Self pollinating (true-breeding)  the plants can pollinate themselves and create identical copies of the parents Trait: a specific characteristic of an individual (example: height or color)(gene) In order to examine how traits were determined, he needed to cross breed his plants (Why?) Each seed had 2 characteristics (alleles) of the same category (example: round vs. wrinkled) Hybrids: the offspring of crosses of parents with different traits

Genes and Alleles Genetic Cross P = Parent generation (1st generation)  Grandparents F1 = 1st offspring (2nd generation)  Parents F2 = 2nd generation (3rd generation)  You Pea Experiment F1 = only one characteristic present (example: round X wrinkled = all round) Mendel’s Conclusions: 1. An individual’s characteristics are determined by factors that are passed from one parental generation to the next Gene: factors that are passed from one parent to the offspring (example: plant color) Alleles: different forms of a gene ( example: trait 1 = yellow / trait 2 = green)

Dominant vs. Recessive Alleles Mendel’s Conclusions Cont. 2. Principle of Dominance: some alleles are dominant (more likely to show) while others are recessive (less likely to show) dominant alleles: alleles that directly affect phenotype—more likely to show (GG) recessive alleles: alleles that are masked unless there are two recessive alleles present—less likely to show (gg) What happens if the genotype is Gg; what is the phenotype? Genotype: genetic makeup Phenotype: physical appearance 2 dominant alleles = dominant phenotype 1 dominant allele + 1 recessive allele = dominant phenotype 2 recessive alleles = recessive phenotype

Segregation F1: Second Generation Cross Mendel wondered about the recessive alleles; were they still present in the plants? Mendel crossed F1 plants to get the F2 generation (third generation) Recessive alleles reappeared in the F2 generation (1/4) Conclusions Segregation: separation of alleles Gametes: sex cells During gamete formation, the alleles for each gene segregate from each other so that each gamete carries only one allele for each gene.

Parent 1 Segregation F1 generation Parent 2