Mendelian genetics

Gregor Mendel

• Father of modern genetics

• Researched with pea plants

•

Gregor Mendel

• Father of modern genetics

• Researched with pea plants

• Developed ideas of dominance and trait segregation

Phenotype

• Phenotype – Physical

characteristics

Genotype

• Phenotype – Physical

characteristics

• Genotype – Genes we inherit

from our parents

Phenotype

– Facial structure

Notice the similarities:

Phenotype

– Facial structure– Eyes

Notice the similarities:

Phenotype

– Facial structure– Eyes– Smile

Notice the similarities:

Phenotype

– Facial structure– Eyes– Smile– Ears

Notice the similarities:

Phenotype

– Facial structure– Eyes– Smile– Ears– Nose

Notice the similarities:

Phenotype

– Facial structure– Eyes– Smile– Ears– Nose– Neck

Notice the similarities:

Mendelian Genetics

Mendel studied a number of characteristics in pea plants including:

• Height - short or TALL

Mendelian GeneticsMendel studied a number of characteristics in pea plants including:

• Height - short or TALL• Seed color - green or YELLOW

Mendelian Genetics

Mendel studied a number of characteristics in pea plants including:

• Height - short or TALL• Seed color - green or YELLOW• Seed shape - wrinkled or ROUND

Mendelian Genetics

Mendel studied a number of characteristics in pea plants including:

• Height - short or TALL• Seed color - green or YELLOW• Seed shape - wrinkled or ROUND• Seed coat color - white or GRAY

Mendelian Genetics

Mendel studied a number of characteristics in pea plants including:

• Height - short or TALL• Seed color - green or YELLOW• Seed shape - wrinkled or ROUND• Seed coat color - white or GRAY • Pod shape - constricted or SMOOTH

Mendelian Genetics

Mendel studied a number of characteristics in pea plants including:

• Height - short or TALL• Seed color - green or YELLOW• Seed shape - wrinkled or ROUND• Seed coat color - white or GRAY • Pod shape - constricted or SMOOTH• Pod color - yellow or GREEN

Mendelian Genetics

Mendel studied a number of characteristics in pea plants including:

• Height - short or TALL• Seed color - green or YELLOW• Seed shape - wrinkled or ROUND• Seed coat color - white or GRAY • Pod shape - constricted or SMOOTH• Pod color - yellow or GREEN• Flower position - terminal or AXIAL

Mendelian Genetics

We will work with the following three:

• Height - short or TALL• Seed color - green or YELLOW• Seed shape - wrinkled or ROUND• Seed coat color - white or GRAY • Pod shape - constricted or SMOOTH• Pod color - yellow or GREEN• Flower position - terminal or AXIAL

Predicting Inheritance

To determine the chances of inheriting a given trait, scientists use Punnett squares and symbols to represent the genes.

UPPERCASE letters are used to represent dominant genes.

lowercase letters are used to represent recessive genes.

Predicting Inheritance

For example:T = represents the gene for TALL in pea plantst = represents the gene for short in pea plants

So:TT & Tt both result in a TALL plant, because T is dominant over t. t is recessive. tt will result in a short plant.

Remember there are two genes for every trait! One from each parent.

Predicting Inheritance

For example:T = represents the gene for TALL in pea plantst = represents the gene for short in pea plants

So:TT & Tt both result in a TALL plant, because T is dominant over t. t is recessive. tt will result in a short plant.

Remember there are two genes for every trait!

Mendels’ Principle of Dominance

Some genes (alleles) are dominant and others are recessive. The phenotype (trait) of a dominant gene will be seen when it is paired with a recessive gene.

Predicting Inheritance

Let’s cross a totally dominant tall plant (TT) with a short plant (tt).Each plant will give only one of its’ two genes to the offspring or F1 generation.

TT x tt

T T t t

Predicting Inheritance

Let’s cross a totally dominant tall plant (TT) with a short plant (tt).Each plant will give only one of its’ two genes to the offspring or F1 generation.

TT x tt

T T t t

Mendels’ “Law” of Segregation

Each gene (allele) separates from the other so that the offspring get only one gene from each parent for a given trait.

Punnett Squares

Tt Tt

Tt Tt

The genes from one parent go here.

The genes from the other parent go here.

Punnett Squares

T T

t Tt Tt

t Tt Tt

Punnett Squares

T T

t Tt Tt

t Tt Tt

Punnett Squares

T T

t Tt Tt

t Tt Tt

Punnett Squares

T T

t Tt Tt

t Tt Tt

Punnett Squares

T T

t Tt Tt

t Tt Tt

Punnett Squares

T T

t Tt Tt

t Tt TtF1 generation

Interpreting the ResultsThe genotype for all the offspring is Tt.The genotype ratio is:

Tt - 4/4

The phenotype for all the offspring is tall.The phenotype ratio is:

tall - 4/4

Punnett Squares

T t

T ?? ??

t ?? ??

Your Turn!!

Punnett Squares

T t

T TT Tt

t Tt ttF2 generation

Punnett Squares

T t

T TT Tt

t Tt tt

Next, give the genotype and phenotype ratios of the offspring (F2 generation).

Punnett Squares

T t

T TT Tt

t Tt tt

Genotype ratio: TT - 1

Punnett Squares

T t

T TT Tt

t Tt tt

Genotype ratio: TT - 1, Tt - 2

Punnett Squares

T t

T TT Tt

t Tt tt

Genotype ratio: TT - 1, Tt - 2, tt - 1

Punnett Squares

T t

T TT Tt

t Tt tt

Genotype ratio: TT - 1, Tt - 2, tt - 1

Phenotype ratio: Tall - 3

Punnett Squares

T t

T TT Tt

t Tt tt

Genotype ratio: TT - 1, Tt - 2, tt - 1

Phenotype ratio: Tall - 3, short - 1

Punnett Squares

T t

T TT Tt

t Tt tt

This is a monohybrid cross. We worked with only one trait. The height of the plant.

Punnett Squares

T t

T TT Tt

t Tt tt

This is a monohybrid cross. We worked with only one trait. The height of the plant.

Later we will work with a dihybrid cross, using the height of the plant and either seed color or seed shape.

two