Gregor Mendel studied heredity by cross-fertilizing pea plants that were purple or white. In the first generation (F1), all plants were purple, showing that purple is dominant over white. When he allowed the F1 plants to self-fertilize, the second generation (F2) resulted in 3 purple plants and 1 white plant. Mendel concluded that each trait is determined by two alleles, one from each parent, and that dominance explains the phenotypes expressed. He represented alleles with letters, like P for purple and p for white, and used terms like homozygous and heterozygous to describe genetic makeup.

1. Unit 10 Lesson 2

2. Gregor Mendel = Father of Genetics
 Used peas to study heredity
 Cross fertilization: he crossed two
parent plants (P) (purple X white) and
got all purple in the first generation
(F1)
 Self fertilization: he allowed two
purple flowers from the first
generation (F1) to self-pollinate to
produce the second generation (F2)
 The end result = 3 purple and 1 white
 Purple is dominant and white is
recessive.


3.  Mendel
concluded that each flower has two
alleles (genes) that determine the
appearance.
 One allele inherited from each parent.
 We use letters to represent the alleles:
 Uppercase letter = dominant
 P = purple
 Lowercase letter = recessive
 p = white
 PP = purple
Pp = purplepp = white

4. homozygous: the alleles are the
same(identical)
 PP = purple
pp = white
 Other examples: HH
hh AA aa
heterozygous: two different alleles
for a trait
 Pp (in this case the dominant allele P is
expressed… so the flower is purple)
 Other examples: HhTtAa

5.  Alleles
can be explained in two ways…
 genotype: the letters that are used
to show the genes.
 Examples: PP, Pp, pp
 phenotype: what the organism looks
like.
 Examples:
purple or white flowers

6. Hh, Aa, Tt, Ww, Aa
brown eyes, tall, narrow
nose, bald
hh, aa, TT, WW, AA, aa, BB, bb
•heterozygous
•homozygous
•genotype
•phenotype
•heterozygous
•homozygous

8. T = tall plant
t = short plant
T
T
T
TT
TT
t
Tt
Tt

9. T = tall plant
50% T T
50% Tt
100%
Tall
t = short plant
T
T
T
TT
TT
t
Tt
Tt

10. a
a