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Transcript 
Gregor Mendel
Book:
“Experiments in Plant
Hybridization”
Why Mendel was successful…



He studied single traits
He used LARGE sample sizes
Introduced Ratios
Terms to KNOW






Allele: 1 of 2 or more different forms of a gene.
Represented as a letter. 2 alleles make a genotype.
Genotype: Genetic Make-up represented as 2
alleles, one from each parent. Ex: “AA, Aa, aa”
Phenotype: Physical Characteristic. Ex: Blue eyes.
Dominant: Allele that will be expressed.
Represented as a capital letter. Ex: “A”
Recessive: Allele that is “hidden.” Represented as
a lower case letter. Ex: “a”
Homozygous: 2 of the same alleles


Example: AA or aa
Heterozygous: 2 different alleles

Example: Aa
MORE Terms to Know

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Monohybrid: Individual that is heterozygous
for one trait. Ex: Aa
Monohybrid Cross: Genetic Cross between
2 heterozygotes. Ex: Aa x Aa
First and Second Parental Generations


P1 and P2
First and Second Filial Generations
(offspring- filial means child in Latin)

F1 and F2
Law of Dominance: If a dominant allele
is present, the dominant phenotype will be
expressed.
Model
Genotype
symbol
Genotype
description
Phenotype
Type of
organism
that exhibits
genotype
RR
Homozygous
Dominant
Round
Pure bred
rr
Homozygous
recessive
Wrinkled
Pure bred
Rr
Heterozygous Round
Hybrid
Law of Segregation

During the formation of gametes (in meiosis),
alleles of gametes separate (segregate).
Each G allele has
separated from the other.
Punnett Square

Diagram showing the possible
combinations of offspring from a genetic
cross
r
r
R
Rr
Rr
Parents
Offspring
R
Rr
Rr
Pisum sativum Pea Plants
P1= round (RR) x wrinkled (rr)
F1 = round (Rr)
r
r
R
Rr
Rr
R
Rr
Rr
P2= round (Rr) x round (Rr)
F2 = 5,474 round, 1,750 wrinkled
R
r
R
RR
Rr
r
Rr
rr
Types of Ratios
1.
2.
Genotypic

Homozygous Dominant : Heterozygous: Homozygous
Recessive
Phenotypic

Dominant : Recessive
Example: genotypic ratio
R
R
r
R
RR RR
Rr Rr
2:2:0 or
________
1:1:0
; phenotypic ratio
4:0 or
_______
1:0
Monohybrid Cross Ratios
R
r
Genotypic Ratio:
R
RR
Rr
1:2:1
Phenotypic Ratio:
r
Rr
rr
3:1
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