PUNNETT PRACTICE

PREDICTING INHERITANCE

• Punnett Squares: diagram that determines the probable distribution of inherited traits in the offspring.

• UPPERCASE letters are used to represent dominant genes (traits).

• lowercase letters are used to represent recessive genes (traits).

HOMOZYGOUS VS. HETEROZYGOUS

Homozygous: Both alleles are the same. Either both capitols (dominant) or both lower-cased (recessive)Example:

• BB (homozygous dominant) • bb (homozygous recessive)

HOMOZYGOUS VS. HETEROZYGOUS

Homozygous: Both alleles are the same. Either both capitols (dominant) or both lower-cased (recessive)Example:

• BB (homozygous dominant) • bb (homozygous recessive)

Heterozygous: Both alleles are different. One capital letter and one lower-cased letter. Example: Bb

WHITE BOARD PRACTICE

WRITE HET OR HOM FOR THE FOLLOWING GENOTYPES

1. RR=

2. Ll=

3. gg=

4. Ee =

WRITE THE GENOTYPES FOR THE FOLLOWING ORGANISMS. USE THE LETTER R

1. A fish is homozygous recessive for fin color

2. A cat is heterozygous for tail length.

WRITE THE GENOTYPES FOR THE FOLLOWING ORGANISMS. USE THE LETTER R

1. A turtle is homozygous dominant for shell color.

2. A polar bear is homozygous recessive for claw length.

WHITE BOARD PRACTICE

SAMPLE PROBLEMSWrite the 3 possible genotypes for eye color. Green eyes are dominant to blue eyes

(use the first letter of the dominant trait)

1. ________

2. ________

3. ________

SAMPLE PROBLEMSWrite the 3 phenotypes for eye color.

Green eyes are dominant to blue eyes

GG=

Gg=

gg=

SAMPLE PROBLEMS

Write the 3 possible genotypes and phenotypes for the following:

Curled toes are dominant to straight toes

(use the first letter of the dominant trait)

1. ________= ________

2. ________= ________

3. ________= ________

PRACTICE PROBLEM #1

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

TT x tt

T T t t

MENDELS’ LAW OF SEGREGATION

T T t t

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

T T t t

TT x t t

CROSS TT X tt BY USING A PUNNETT SQUARE

Tt Tt

Tt t

The genes from one parent go here.

The genes from the other parent go here.

T T

t Tt Tt

t Tt Tt

CROSS TT X tt BY USING A PUNNETT SQUARE

T T

t Tt Tt

t Tt Tt

If a box receives a capital letter and a lower-cased letter we write the capitol letter first

CROSS TT X tt BY USING A PUNNETT SQUARE

INTERPRETING THE RESULTS

Possible offspring Genotype =

Possible offspring Genotype = Tt.What percent of offspring will have the following genotypes:

TT=Tt=tt=

INTERPRETING THE RESULTS

INTERPRETING THE RESULTS

Possible offspring Genotype = Tt.What percent of offspring will have the following genotypes:

TT= Tt= tt=

INTERPRETING THE RESULTS

Possible offspring Genotype = Tt.What percent of offspring will have the following genotypes:

TT= 0%Tt= 100%tt= 0%

Possible offspring phenotype =

INTERPRETING THE RESULTSPossible offspring Genotype = Tt.What percent of offspring will have the following genotypes:

TT= 0%Tt= 100%tt= 0%

Possible offspring phenotype = tall.What percent of offspring will have the following phenotypes:

Tall=Short=

INTERPRETING THE RESULTSPossible offspring Genotype = Tt.What percent of offspring will have the following genotypes:

TT= 0%Tt= 100%tt= 0%

Possible offspring phenotype = tall.What percent of offspring will have the following phenotypes:

Tall= 100%Short= 0%

PRACTICE PROBLEM #2

Black rabbits are dominant to brown. Two heterozygous rabbits have offspring. Predict what percentage of their offspring will be brown.

PRACTICE PROBLEM

Black rabbits are dominant to brown. Two heterozygous rabbits have offspring. Predict what percentage of their offspring will be brown.

Step 1: Determine the genotype of parents. Always use the first letter of the dominant trait. ____________x _____________

Step 2: Set up a Punnett SquareStep 3: Complete Punnett SquareStep 4: Predict offspring phenotype

PRACTICE PROBLEMBlack rabbits are dominant to brown. Two heterozygous rabbits have offspring. Predict what percentage of their offspring will be brown?

% Black= _____% Brown= _____

WHITE BOARD PRACTICE

Tall plants are dominant to short. Cross two heterozygous pea plants.

1. Determine parent’s genotype and write on whiteboard

Set up a punnett square and fill it in.

Hold up whiteboard

PUNNETT SQUARES

T t

T TT Tt

t Tt tt

Determine the genotype percentages and write on whiteboard

1. TT=2. Tt=3. Tt=

Determine the Phenotype percentages and write on whiteboard

• Tall=• Short=

ONE MORE WHITEBOARD PRACTICERound seeds are dominant to wrinkled seeds.

Rr x rr    What percentage of the offspring will be round? _______________