MENDEL’S LEGACY

CH. 9

Gregor Mendel (1823-1884)

The Father of Modern Genetics!

Mendel taught natural science to High School Students. Once: he crossed peas and

mice of different varieties “for the fun of the thing”

He determined several “laws” of inheritance....

Mendel’s work became the foundation for Modern Genetics.

Mendel’s peas

MENDEL chose a common garden pea (Pisum) for his first experiments in hybridization

Mendel’s Procedure

Step ONE: find plants that are “pure” for one trait (like height).

Call them: P1

Step TWO: take opposites for the trait (like tall X short) & cross pollinate/fertilize

Step 3: grow offspring and record results. (F1 = filial = offspring)

Step 4: Allow self-pollination & grow the grandchildren of P1. Call this group F2. Record results.

P1 = HH (tall) X hh (short)

Results: All F1 grew tall!

F1 X F1 = F2

Results, 3/4th peas were tall, 1/4th peas were short!

Mendel discovered...

...some traits are “masked”...they are RECESSIVE and may skip generations.

...some traits are DOMINANT...they occur often in the population.

...traits are determined by a pair of factors.

Alleles

Mendel determined...

The pair of “factors” are sorted independently of each other.

These factors are separated when the gametes are formed.

HOW TO PLAY GENETICS “GAMES” Traits are expressed as letters

of the alphabet. HH or hh Capital letters denote dominant

traits

HH or hh are pure strains. They are called HOMOZYGOUS

Hh are mixed strains....carriers of the recessive gene, but do not look recessive. They are called HETEROZYGOUS

EXAMPLES

H = TALL h = short HH = homozygous tall hh = homozygous short Hh = heterozygous tall

More vocabulary....

genotype = the letters we use to express traits = genetic makeup

phenotype = what something looks like.

Phenotypes

fat pod, smooth peas

or...

skinny pods, wrinkled peas