1. Punnett Squares
JH-KEADLE

2. Punnett Square
When Gregor Mendel studied pea plants, he noticed patterns in some of the traits.
In some cases, you can predict what traits offspring will have based on the parent’s genetics.
A Punnett Square is a useful tool for predicting traits.

3. Punnett Square
Punnett square – a graphic used to predict the possible genotypes of offspring in a given cross.
Each parent has two alleles for a particular gene.
An offspring receives one allele from each parent.

4. Punnett Square
To set up a Punnett Square, decide which trait is dominant.
dominant trait = capital letter
recessive trait = lower case letter
One parent’s alleles are placed at the top.
The other parent’s alleles are placed along the side.

6. Results of the Punnett Square
Each individual from the Punnett Square will have a genotype and a phenotype.
genotype – what the genes are (the letters).
phenotype – what the trait looks like.

7. homozygous- both alleles are dominant or both are recessive
homozygous- both alleles are dominant or both are recessive. (so you see either two uppercase or two lower case letters.
heterozygous – each allele is different. (You will see one capital and one lower case).

8. P P p p Pp Pp Pp Pp Punnett Square Use P for purple flower color
Use p for white flower color
homozygous P P p Pp Pp
homozygous p Pp Pp

9. P p P p PP Pp pp Pp Punnett Square Cross two heterozygous plants

10. Results of the Punnett Square
Punnett Results
Genotype
Phenotype PP
Homozygous dominant
Purple Flowers Pp
Heterozygous pp
Homozygous recessive
White Flowers

12. Results of the Punnett Square
The results of a Punnett square will give you the probability of certain outcomes.
Results are usually written as a ratio or a percent.

14. Complete dominance
complete dominance – the dominant allele hides the recessive. The phenotype will be the dominant characteristic.
You can use a Punnett square and will have two genotypes. RR rr Rr X =

15. Punnett Square Practice
A dog breeder is mating a brown heterozygous lab to a black homozygous lab. Brown is dominant. Set up a Punnett Square and decide what percent of the offspring will be black and brown. ? X =

16. b B b Bb bb Bb bb b Bb One parent is heterozygous brown
B = brown
b = black Bb
One parent is heterozygous brown
One parent is homozygous black bb b B b Bb bb Bb bb b

17. Bb Bb bb bb 50% are brown, 50% are black brown brown black black
Phenotype
Genotype Bb
brown Bb
brown bb
black bb
black
50% are brown, 50% are black

19. Incomplete Dominance = X
Some traits are not dominant or recessive
incomplete dominance – each allele can affect the phenotype. These traits will blend when heterozygous.
You can use a Punnett square and will have 3 genotypes instead of two RR rr Rr = X

20. Punnett Square Practice
In purple people eaters one eye is homozygous dominant, two eyes is homozygous recessive, and three eyes is heterozygous. The number of eyes in an incomplete dominant trait. What would the offspring look like from a homozygous recessive purple people eater and a homozygous dominant purple people eater? Set up a Punnett Square and find the genotypes and phenotypes of the offspring.

21. E E e Ee Ee Ee Ee e EE = one eye ee = two eyes Ee = three eyes
One parent is homozygous dominant
One parent is homozygous recessive EE ee E E e Ee Ee Ee Ee e

22. Ee Ee Ee Ee 100% three eyed 3 eyes 3 eyes 3 eyes 3 eyes Phenotype
Genotype Ee
3 eyes Ee
3 eyes Ee
3 eyes Ee
3 eyes
100% three eyed

24. Codominance = X = Some traits are not dominant or recessive
codominance – both of the alleles contribute to the phenotype. The individual will have traits of both phenotypes.
You can use a Punnett square and will have 3 genotypes instead of two. = X =

25. Punnett Square Practice
In snakes, certain colors can be codominant. For our example, we will look at the yellow color in boas. Yellow and White are co-dominant. What results would you get with a homozygous yellow parent and a homozygous white parent? ? = X

26. Y Y y Yy Yy Yy Yy y YY yy Y = yellow y = white
One parent is homozygous yellow
One parent is homozygous white yy Y Y y Yy Yy Yy Yy y

27. Phenotype
Genotype Yy
pied Yy
pied Yy
pied Yy
pied
100% are pied

29. (blue is dominant to yellow)
Color in and complete the following chart based on the type of inheritance. Assume parents are homozygous. X
complete dominance
(blue is dominant to yellow)
incomplete dominance
codominance