Download Genetics PPT #1

MENDEL’S LEGACY
CH. 11
Gregor Mendel (1823-1884)
The Father of
Modern
Genetics!
 Once:
he crossed peas and
mice of different varieties “for
the fun of the thing”
 He
determined several “laws”
of inheritance....
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 (each genotype has
2 alleles)
 Capital letters denote dominant
traits
 HH
or hh are pure strains. They
are called HOMOZYGOUS
 Hh are mixed strains (hybrid)
....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