MENDEL MEIOSIS Gregor Mendel Austrian Monk 1822 1884

MENDEL & MEIOSIS

Gregor Mendel • Austrian Monk • 1822 -1884 • Father of Genetics

Genetics • Branch of biology that studies heredity.

Heredity • The passing on of characteristics from parents to offspring.

Traits • Characteristics that are inherited –Eye color –Size –Hair, skin color –etc.

Choosing a subject • Mendel chose garden peas because –Easy to grow –Produce many offspring –Can be self-pollinated

See drawing of typical flower • Garden peas produced both egg and sperm. • Gametes - sex cells

• Pollination - transfer of male pollen grains to pistil of flower. –Self pollination - occurs when pollen is transferred to the pistil of the same flower or plant.

• Cross pollination - occurs when the pollen of one plant is transferred to the pistil of a different plant.

• Fertilization - the uniting of the male and female gametes.

• Pure breed - an organism that is true breeding for a trait. • Hybrid - offspring of parents that have different forms of a trait.

• Monohybrid crosses - A cross between two parents differing by one trait. • See example.

Seven Traits • Seed shape, Seed color • Flower color, Flower position • Pod color , Pod shape • Plant height

Mendels Principles • Principle of Dominance • Principle of Segregation • Principle of Independent assortment

Principle of Dominance • One gene in a pair may mask the other gene, preventing it from having an effect.

Principle of Segregation • The two factors for a characteristic segregate or separate during formation of eggs and sperm.

Principle of Independent Assortment • Traits are inherited independently of each other.

Allele • Different manifestation of a trait. –Example: Trait = height –Different manifestations are tall and short.

Phenotype • Outward manifestation of a trait. • It is what you see. • The plant is: Tall, Blue, smelly, etc.

Genotype • Actual gene combination from both parents. • Example: TT, Tt, tt.

Homozygous • Both alleles for a trait are the same. • Example: tt, TT

Heterozygous • The two alleles for a trait differ from one another. • Example: Tt

Monohybrid cross • A cross between two parents differing by a single trait. • Example: short pea plant crossed to a tall pea plant

Dihybrid cross • A cross between two parents involving two different traits. • Example: Round yellow seeds crossed to wrinkled green seeds.

Reginald Punnett, 1905 • Developed the Punnett square. • Shortcut method for finding expected proportions of possible genotypes.

Calculating probability • Divide the number of desired outcomes by the total number of possible outcomes. • Example: Heads or tails = 2 possible outcomes. Heads desired = 1 desired outcome. 1/2 =1: 2

Test cross • Used to determine if an organism is homozygous dominant or heterozygous. • Cross the unknown with a homozygous recessive.