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

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

symbolGenotype 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 SquareDiagram showing the possible

combinations of offspring from a genetic cross

r r

R Rr Rr

R Rr Rr

Parents

Offspring

R r

R RR Rr

r Rr rr

r r

R Rr Rr

R Rr Rr

Pisum sativum Pea PlantsP1= round (RR) x wrinkled (rr)

F1 = round (Rr)P2= round (Rr) x round (Rr)

F2 = 5,474 round, 1,750 wrinkled

Types of Ratios1. Genotypic

Homozygous Dominant : Heterozygous: Homozygous Recessive

2. Phenotypic Dominant : Recessive

Example: genotypic ratio ________ ; phenotypic ratio _______

RR RR

Rr Rr

R

R

r

R

2:2:0 or 1:1:0

4:0 or 1:0

Monohybrid Cross Ratios

RR Rr

Rr rr

R

R

r

r

1:2:1Genotypic Ratio:

Phenotypic Ratio:

3:1