1. Punnett Squares
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2. Used to calculate the probability of inheriting a particular trait
Punnett Squares
Punnett Square – model for predicting all possible genotypes resulting from a cross (mating)
Used to calculate the probability of inheriting a particular trait
Probability – The chance that a given event will occur

3. Monohybrid Crosses
Monohybrid Crosses – involve only one trait
The “normal” Punnett Square

4. Monohybrid Cross Parent 1: Aa Parent 2: Aa Parent 1’s Gametes
Offspring

5. How to Complete a Punnett SquareAa aa

6. Genotypes:
1 AA : 2 Aa : 1 aa
This means there is a 25% chance of inheriting the AA genotype, a 50% chance of inheriting the Aa genotype, and a 25% chance of inheriting the aa genotype.
We can use the Punnett Square above to figure out the ratios of genotypes and phenotypes.
Let’s say A = black and
a = albino (no color).

7. Phenotypes:
3 Black : 1 Albino
This means there is a 75% chance of inheriting the black phenotype, and a 25% chance of inheriting the white phenotype.
We can use the Punnett Square above to figure out the ratios of genotypes and phenotypes.
Let’s say A = black and
a = albino (no color).

8. You Try It Now!
Give the genotype and phenotype ratios for the following cross: TT x tt (T = Tall and t = Short)

9. Step One: Set Up Punnett Square (put one parent on the top and the other along the side)

10. Step Two: Complete the Punnett Square

11. Tt t Genotype: 4 - Tt Phenotype: 100% Tall Remember: Each box is 25%
Step Three: Write the genotype and phenotype
T T t Tt
Genotype:
4 - Tt
Phenotype:
100% Tall
Remember: Each box is 25%

12. You Try It Now!
Give the genotype and phenotype ratios for the following cross: Tt x tt

13. Step One: Set Up Punnett Square (put one parent on the top and the other along the side)

14. Step Two: Complete the Punnett Square

15. Tt tt t Genotype: Tt - 2 (50%) tt - 2 (50%) Phenotype: 50% Tall
Step Two: Complete the Punnett Square
T t t
Genotype:
Tt - 2 (50%)
tt - 2 (50%)
Phenotype:
50% Tall
50% Short Tt tt
Remember: Each box is 25%

16. Complete the punnett square
Round seeds are dominant to wrinkled:
Cross Rr x Rr
What are the possible genotypes?
What are the possible phenotypes?
What’s the probability the offspring will be round?
What’s the probability the offspring will be wrinkled?

17. Monohybrid Cross Practice
1. Which one represents a dominant allele? G g
2. Which one represents a recessive allele? F f
3. Which one represents a homozygous dominant genotype? TT Tt tt

18. 4. Which one represents a homozygous recessive genotype? RR Rr rr
5. Which one represents a heterozygous genotype? WW Ww ww
6. If purple eyes are dominant to pink eyes, which genotype(s) would result in purple eyes? PP Pp pp
7. If an organism is heterozygous and has brown fur, which trait is dominant? brown fur white fur