GeneticsGenetics

Gregor MendelGregor Mendel

“Father of Genetics”1866- published findings on plant breeding and inheritance

(During American Civil War)Not discovered until early 1900s

“Father of Genetics”1866- published findings on plant breeding and inheritance

(During American Civil War)Not discovered until early 1900s

Keys to SuccessKeys to SuccessUsed “True-Breeding” pea plants (“purebreds”)Always produce offspring with only one form of a trait

Studied only 1 characteristic at a time

Analyzed data mathematically

Used “True-Breeding” pea plants (“purebreds”)Always produce offspring with only one form of a trait

Studied only 1 characteristic at a time

Analyzed data mathematically

Pea Plant ReproductionPea Plant Reproduction

1. Self-pollination Pollen fertilizes egg cells on

same flower 1 parent

2. Cross-pollination Pollen from flower of one plant

fertilizes egg cells on another plant

2 parents

1. Self-pollination Pollen fertilizes egg cells on

same flower 1 parent

2. Cross-pollination Pollen from flower of one plant

fertilizes egg cells on another plant

2 parents

Mendel controlled breeding by cross-pollinating

To prevent self-pollination, Mendel removed male parts from a flower and dusted the flower with pollen from a different pea plant

Mendel controlled breeding by cross-pollinating

To prevent self-pollination, Mendel removed male parts from a flower and dusted the flower with pollen from a different pea plant

Genetics:The science of heredity

Heredity:The biological inheritance of traits from parent to offspring

Genetics:The science of heredity

Heredity:The biological inheritance of traits from parent to offspring

Genetics used for:Genetics used for:

1.Preventing & treating diseases

2.Developing tougher plants to increase food production

1.Preventing & treating diseases

2.Developing tougher plants to increase food production

GenerationsGenerations1. P generation: parent generation

“true - breeding”

2. F1 generation First generation of offspring

3. F2 generation Second generation produced

when f1 generations are crossed

1. P generation: parent generation “true - breeding”

2. F1 generation First generation of offspring

3. F2 generation Second generation produced

when f1 generations are crossed

AlleleThe different forms of a gene2, 3, or even 12 possible alleles per gene

AlleleThe different forms of a gene2, 3, or even 12 possible alleles per gene

Dominant

Form of the gene that is expressed

Capital letter: T

Dominant

Form of the gene that is expressed

Capital letter: T

Recessive

Form of a gene (allele) that is only expressed in homozygous state

Lowercase letter: t

Recessive

Form of a gene (allele) that is only expressed in homozygous state

Lowercase letter: t

Homozygous

2 identical alleles for the same trait

Homozygous dominant: TTHomozygous recessive: tt

Homozygous

2 identical alleles for the same trait

Homozygous dominant: TTHomozygous recessive: tt

Heterozygous

2 different alleles for the same trait

Tt : dominant trait will be expressed

Also called a “hybrid”

Heterozygous

2 different alleles for the same trait

Tt : dominant trait will be expressed

Also called a “hybrid”

Genotype

Genetic make-up of an organism

The “letters”Tt or TT or ttAa or AA or aa

Genotype

Genetic make-up of an organism

The “letters”Tt or TT or ttAa or AA or aa

Phenotype

Physical expression of a trait

Ex: Tall or Short

Phenotype

Physical expression of a trait

Ex: Tall or Short

Examples:

TT = genotypeTall = phenotype

tt = genotypeShort = phenotype

Examples:

TT = genotypeTall = phenotype

tt = genotypeShort = phenotype

Law of segregationLaw of segregation

The two alleles for each trait separate during meiosis

So, for each gene, an organism receives one allele from each parent - during fertilization

The two alleles for each trait separate during meiosis

So, for each gene, an organism receives one allele from each parent - during fertilization

Part 2Part 2

Seed ColorSeed Color P generation cross: (“true -

breeding”)Yellow peas x Green peas

F1 generation:All yellow

F2 generation:6022 yellow : 2001 green3 yellow : 1 green

P generation cross: (“true - breeding”)Yellow peas x Green peas

F1 generation:All yellow

F2 generation:6022 yellow : 2001 green3 yellow : 1 green

Monohybrid crossMonohybrid cross

Use a Punnett square to cross 2 hybrids:

Yy x Yy What are the possible

genotypes?

What is the genotypic ratio?

What is the phenotypic ratio?

Use a Punnett square to cross 2 hybrids:

Yy x Yy What are the possible

genotypes?

What is the genotypic ratio?

What is the phenotypic ratio?

Law of Independent Assortment

Law of Independent Assortment

Genes on separate chromosomes sort independently during meiosis

Alleles for seed shape separate independently from seed color alleles

So, seed shape is not connected to seed color

Genes on separate chromosomes sort independently during meiosis

Alleles for seed shape separate independently from seed color alleles

So, seed shape is not connected to seed color

Dihybrid crossDihybrid cross

A Special type of two - factor cross

YyRr x YyRr (heterozygous for both traits)

You will always find the same phenotypic ratio. What is this ratio?

A Special type of two - factor cross

YyRr x YyRr (heterozygous for both traits)

You will always find the same phenotypic ratio. What is this ratio?