Pedigree Charts

How to work Dominant and Recessive Genetic Problems with a Pedigree Chart

Pedigree Charts

Besides showing possible gene pairings, a pedigree chart gives the probability of each pairing.

It shows how often, on the average, a given pairing will occur.

Pea Plant Characteristics

Show a cross between a tall and short pea plant Step One Write down the set of contrasting traits.

Assign the capitol letter to the dominant trait and the lower case letter to the recessive trait.

Tall T Short t

Show a cross between a tall and short pea plant Step Two

Write down possible

genotypes

and

phenotypes .

TT Tall Tt tt Tall Short

Show a cross between a tall and short pea plant Step Three

Fill in the genotypes of the parents on the pedigree chart.

P 1

Pedigree Chart

P 2 F 1

Parents

TT tt P 1 P 2 In the circle - the possible gametes of the female are listed.

In the square - the possible gametes of the male are listed

Show a cross between a tall and short pea plant Step Four

Fill in the genetic possibilities of the F

1

on the pedigree chart.

Cross between a tall and short pea plant

P 1

T T t t

P 2

T t

Take first gene from the female and first gene from F 1 the male and place in the first offspring spot.

Cross between a tall and short pea plant

P 1

T T t t

P 2

T t T t

F 1 Take first gene from the female and second gene from the male and place in the second offspring spot.

Cross between a tall and short pea plant

P 1

T T t t

P 2

T t T t T t

F 1 Take second gene from the female and first gene from the male and place in the third offspring spot.

Cross between a tall and short pea plant

P 1

T T t t

P 2

T t T t T t T t

Take second gene from the female and second gene F 1 from the male and place in the fourth offspring spot.

Show a cross between a tall and short pea plant Step Five

Write down the

genotypic ratio

and the

phenotypic ratio

.

Purebred dominant : Hybrid : Purebred recessive Tall : Short

Cross between a tall and short pea plant

P 1

T T t t

P 2

T t T t 0:4:0 4:0 Genotypic Ratio Phenotypic Ratio T t T t

F 1

Pedigree

A pedigree is a visual tool for following a trait through generations of a family.

F 1 F 2

Pedigree

Males are represented by squares and females by circles.

Male Female

Pedigree

• A completely filled circle or square shows • that the trait is seen in that person.

Half-colored circles or squares indicate carriers. A carrier is heterozygous for the trait, • and it is not seen.

An empty circle or square means they do not have the trait and they are not carriers