Mendel and

Meiosis

Gregor Mendel HeredityHeredity is the passing of

characteristics from parents to offspring.

GeneticsGenetics is the study of heredity or how those traits are inherited.

Gregor Mendel was the first person to succeed in predicting how traits were inherited thus he became known as the Father of Genetics.Father of Genetics.

Gregor Mendel Gregor Mendel is best known for his

study of pea plantspea plants. He used pea plants because they

have 2 distinct sex cells called gametesgametes.

Mendel pollinated the flowers himself by transferring the male pollen to the stigmastigma of the flower (pollination).(pollination).

Pollen

Uniting of the male and female gametes is called fertilizationfertilization.

Mendel cross-pollinatedcross-pollinated pea plants in order to study the various traits:

DominaDominantnt: the trait that was

observed

RecessiveRecessive: the trait

that disappear

ed.

Crossing traits PurebredPurebred: a cross between plants with

identical traits. HybridHybrid: a cross between plants with different

traits like tall and short. Mendel’s first cross he called a monohybridmonohybrid

cross. (Mono means one) Later Mendel began crossing plants with 2

traits. These crossed were called dihybriddihybrid crosses.

Testcross: Breeding an individual of unknown genotype to a homozygous recessivehomozygous recessive individual to reveal the unknown genotype

Parent generat

ion

Filial (son or

daughter) generation

2nd Filial

generation

Grandchildren

Children

Parents

Genotypes and Phenotypes?? PhenotypePhenotype – the way that the

organism lookslooks and behaves.PhenoPheno (physical) (physical) typetype (model) (model)

Genotypesenotypes – the combination of genesgenes in the organism.

GenGen (birth) (birth) typetype (model) (model)

Genotypes and Phenotypes

PhenotypePhenotype

GenotypeGenotype

Genotypes and Phenotypes Homozygous dominant:

Homo (same)

Homozygous recessive:

Heterozyous: Hetero (different)

Mendel’s Laws of Inheritance Law of segregation:Law of segregation: the 2 genes

for each trait will segregatesegregate during the formation of the gametesgametes.

Mendel’s Laws of Inheritance Law of independent assortment: Law of independent assortment:

Each trait (or gene) is inherited Each trait (or gene) is inherited independently of the other independently of the other traitstraits.

In other words, all blondes do not have blue eyes.

Punnet Squares In 1905, Reginal PunnetPunnet, an

English biologist, devised a shorthand way of predicting the outcomes of the various crosses.

These are called Punnet squares.

Monohybrid crosses

Genotypes

Phenotypes

BB: 1…25%Bb: 2…50%bb: 1…25%

White: 3…75%(BB and Bb)black: 1…25%

BB: White

bb: Black

Dihybrid crosses