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.

7. Cut out your graphic

8. Results of the Punnett Square
genotype – The allele combination of the organism (letters).

9. Results of the Punnett Square
phenotype – the way an organism looks or behaves.

10. homozygous- When two alleles for the trait are the same. (TT or tt)

11. heterozygous – When alleles for a trait are different. (Tt)

12. 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

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

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

16. 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.

18. 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 =

19. Punnett Square Practice
Some trolls have one eye (EE, Ee) while others have two (ee). Two heterozygous one-eyed trolls are crossed. ? X =

20. e E E EE Ee Ee ee e Ee One parent is heterozygous one eye Ee
EE, Ee = one eye
ee = two eyes
One parent is heterozygous one eye Ee Ee e E E EE Ee Ee ee e

21. EE Ee Ee ee Genotype ratio: Phenotype ratio: one eye one eye one eye
two eye
Genotype ratio:
1:2:1
Phenotype ratio:
3:1

23. Punnett Square Practice
In dragons, red (R) is dominant over green (r). A homozygous red dragon (RR) is crossed with a heterozygous red dragon (Rr). ? X =

24. R R R RR RR Rr Rr r RR One parent is heterozygous one eye Rr
RR, Rr = red
rr = green
One parent is heterozygous one eye RR Rr R R R RR RR Rr Rr r

25. RR RR Rr Rr red red red red What are the possible genotypes? RR and Rr
Phenotype
Genotype RR
red RR
red Rr
red Rr
red
What are the possible genotypes?
RR and Rr
What are the possible phenotypes?
red

27. 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

28. 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.

29. 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

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

33. 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 =

34. 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

35. 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

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

39. (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