Mendel and

Meiosis

Learning Goal:predict possible outcomes of various genetic combinations such as monohybrid crosses

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.

Genotypes and Phenotypes PhenotypePhenotype – the way that the

organism lookslooks and behaves.

PhenoPheno (physical) (physical) typetype (model) (model)

Genotypesenotypes – the combination of alleles (genes)alleles (genes) in the organism.

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

Genotypes and Phenotypes AlleleAllele – the different forms of a gene

ex: Blue eyes or Brown eyes Alleles can be dominant or recessive

DominantDominant The trait covers up (masks) the

recessive trait Symbol is a capital letter (T)

RecessiveRecessive The trait is masked by the dominant

allele Symbol is a lowercase letter (t)

Genotypes and Phenotypes

PhenotypePhenotype

Genotype Genotype

AllelesAlleles

Genotypes and Phenotypes Homozygous dominant:

Homo (same)

Homozygous recessive:

Heterozygous: Hetero (different)

Crossing 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 crosses were called dihybriddihybrid crosses.

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

Parent generat

ion

Filial (son or

daughter) generation

2nd Filial

generation

Grandchildren

Children

Parents

Law of segregation:Law of segregation: the 2 alleles for each trait (on homologous chromosomes)will segregatesegregate (separate)(separate) with the formation of the gametes gametes during meiosis.

Mendel’s Laws of Inheritance

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.

Punnett Squares In 1905, Reginald PunnettPunnett, an

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

These are called Punnett squares.

Monohybrid crosses

Genotypes

Phenotypes

Bb: 100% Bb

100% White

B: White

b: Black

BB

bb

Bb Bb

Bb Bb

B B

b

b

gametes

Monohybrid crosses

Genotypes

Phenotypes

BB: 25%Bb: 50%bb: 25%

White: 75%(BB and Bb)black: 25%

B: White

b: BlackBB Bb

Bb bb

Genotypic ratio1:2:1

Phenotypic ratio3:1

B b

B

b

gametes

Monohybrid crosses

Genotypes

PhenotypesBB: 0%

Bb: 50% bb: 50%

Genotypic ratio

0:1:1

50% White50% Black

Phenotypic ratio

1:1

BB: White

bb: Black

Bb

bb

B b

b

b

Bb bb

Bb bb

gametes