Punnett Squares
Punnett Squares are used to find the probability of genes for an offspring.
Each square is a 25% chance of what each offspring will look like, containing the allele combinations from both parents' genotypes.
When working with letter that look the same in capitals and lowercase, write the lowercase letter in cursive
Example: S & s, P &p, etc
*In genotypes, the DOMINANT allele is always first and is represented all throughout.
Each square is a 25% chance of what each offspring will look like, containing the allele combinations from both parents' genotypes.
When working with letter that look the same in capitals and lowercase, write the lowercase letter in cursive
Example: S & s, P &p, etc
*In genotypes, the DOMINANT allele is always first and is represented all throughout.
How To Solve
Step 1
![Picture](/uploads/2/6/8/8/26882988/1394930571.jpg)
Draw a box that is large enough to write in and divide it into 4 parts
Step 2
![Picture](/uploads/2/6/8/8/26882988/1394930665.jpg)
Write the parent's alleles on each side of the box
In this example we're using A
A is dominant
a is recessive
In this example we're using A
A is dominant
a is recessive
Step 3
![Picture](/uploads/2/6/8/8/26882988/1394930830.jpg)
Match the alleles together using the box as a guide
Step 4
Count the genotypes in each box and find the percentages
In the example, the combinations are AA and Aa*
This would mean that the offspring would have a 100% chance of having the dominant trait and a 0% chance of having the recessive trait
In the example, the combinations are AA and Aa*
This would mean that the offspring would have a 100% chance of having the dominant trait and a 0% chance of having the recessive trait
Practice Problems
1. If Mary's parents both have heterozygous brown eyes and brown eyes are dominant to green eyes, what are the chances of Mary having green eyes?
2. Red hair is recessive to brown hair. If Harry's mom has red hair and Harry's dad has heterozygous brown hair, what is the probability of Harry having brown hair?
3. If the tall pea plant gene is dominant to the short pea plant gene, then what is the probability of getting a short pea plant when 2 heterozygous pea plants are crosses with one another?
2. Red hair is recessive to brown hair. If Harry's mom has red hair and Harry's dad has heterozygous brown hair, what is the probability of Harry having brown hair?
3. If the tall pea plant gene is dominant to the short pea plant gene, then what is the probability of getting a short pea plant when 2 heterozygous pea plants are crosses with one another?