Pioneer of Genetics: Gregor Mendel Gregor Mendel was an Austrian monk whose experiments with garden peas laid the foundation for the science of genetics Mendel’s work provided a basis for understanding heredity 1822 - 1884

Why did Mendel choose the garden pea? Identifiable characteristics Page 130, Fig 2 Plant reproduction: self and cross-fertilizing

Plant reproduction Male – Stamen Female – Carpel Fertilization occurs when pollen produced by the stamen attaches to the carpel, this is known as pollination

Mendel cross-pollinated the pea plants Started with pure breeding plants – those that only produce identical offspring. Ex) tall plants only produce other tall plants

The first generation was all purple! The purple trait masked the white flower trait! F1 generation or first filial

Mendel’s explanation He called the purple trait dominant because it masked the white trait. He represented it with a capital P He called the white trait recessive and represented it with a lower case p Each copy of the trait (gene) is called an allele, one allele comes from each parent. These alleles separate, or segregate, during the formation of sex cells.

Some more terminology Genotype refers to the alleles an organism contains for a particular trait (Pp) Phenotype refers to the observable trait (purple) Homozygous: a genotype in which the alleles of a pair are the same Heterozygous: a genotype in which the alleles of a pair are different Monohybrid cross: a cross that involves only one trait

Mendel created a second generation by allowing the F1s to self-pollinate F1 generation Pp Pp Meiosis occurs. Each gamete has one of the homologous chromosomes. P p P p PP Purple Pp Purple Pp Purple pp White F2 generation inherits alleles from the gametes of the F1 75% purple, 25% white

Cross simulation using Punnett squares Cross 1 (pure breeding plants) White parent pp p P Gametes Pp Phenotypic Ratio 100% purple PP Purple parent

Cross simulation using Punnett squares Cross 2 (self pollination) Purple parent Pp P p Gametes PP Pp Phenotypic Ratio 75% purple 25% white Pp Pp pp Purple parent

Mendel’s Laws of Inheritance Each parent contributes one allele. If a pure-breeding plant self-fertilizes, each offspring receives two copies of the same allele. Dominant alleles are always expressed when a recessive allele is present. Each pair of alleles segregates during the formation of sex cells.