Mendelian Genetics

Responsible for the Laws governing Inheritance of Traits

?

Gregor Mendel(1822-1884)

Gregor Johann Mendel

Austrian monk

Studied the inheritance of traits in pea plants

Between 1856 and 1863, Mendel cultivated and tested some 28,000 pea plants

He found that the plants' offspring retained traits of the parents

Called the “Father of Genetics"

Particulate Inheritance

Mendel stated that physical traits are inherited as “particles”

Mendel did not know that the “particles” were actually DNA and Chromosomes

Genetics

Genetics - study of heredity

Heredity

the passing of traits from parent to offspring

Monohybrid cross + Dihybrid cross

Monohybrid cross - cross involving a single traite.g. flower color

Dihybrid cross - cross involving two traits e.g. flower color & plant height

Dominant
Recessive

stronger of two genes expressed in the hybrid therefore trait shows over other trait; represented by a capital letter (R)

gene that shows up less often in a cross; represented by a lowercase letter (r)

Genotype

gene combination or make up for a trait (e.g. RR, Rr, rr)

Phenotype

the physical feature (what you see) resulting from a genotype (e.g. red, white)

Homozygous genotype
Heterozygous genotype

gene combination involving 2 dominant or 2 recessive genes (e.g. RR or rr); also called pure - remember homo means ‘same’

gene combination of one dominant & one recessive allele (e.g. Rr); also called hybrid

Why peas, Pisum sativum?

Can be grown in a small area

Produce lots of offspring

Produce pure plants when allowed to self-pollinate several generations

Can be artificially cross-pollinated

Mendel’s Experimental Methods

Mendel hand-pollinated flowers using a paintbrush

He could snip the stamens to prevent self-pollination

Covered each flower with a cloth bag to prevent cross pollination

He traced traits through the several generations

How Mendel Began

Mendel produced pure strains by allowing the plants to self-pollinate for several generations

Eight Pea Plant Traits

Seed shape --- Round (R) or Wrinkled (r)

Seed Color ---- Yellow (Y) or Green (y)

Pod Shape --- Smooth (S) or wrinkled (s)

Pod Color --- Green (G) or Yellow (g)

Seed Coat Color ---Gray (G) or White (g)

Flower position---Axial (A) or Terminal (a)

Plant Height --- Tall (T) or Short (t)

Flower color --- Purple (P) or white (p)

Parental P1 Generation
F1 generation
F2 generation

= the parental generation in a breeding experiment. The first set of individuals mated.

= the first-generation offspring in a breeding experiment. (offspring from the P1 – often referred to as 1st filial generation)

= the second-generation offspring in a breeding experiment. (From crossing individuals from the F1 generation) (2nd filial generation)

He noticed that some traits even skipped generations.