Predicting Traits with Punnett Squares

Science · Ecosystems & Habitats · ages 13-14

Name ______________________ Date ____________

An allele that shows up in the body even when only one copy is present is called what?
- Recessive
- Dominant
- Genotype
What do we call the different versions of a gene, like the version for brown eyes and the version for blue eyes?
- Alleles
- Chromosomes
- Phenotypes
A recessive allele can show up in a person's body even if they only have one copy of it.
Circle one: True False
A Punnett square for Bb x Bb has 4 boxes: BB, Bb, Bb, bb. How many of the boxes have at least one dominant B allele?
Answer: ______________
In a Punnett square for Bb x Bb, how many of the 4 boxes come out bb?
- 1
- 2
- 3
Mia's genotype is Bb. What does 'genotype' mean here?
- The trait you can see, like her eye color
- The combination of alleles she carries
- How many chromosomes she has
Two pea plants that are both Tt (T = tall, dominant; t = short, recessive) are crossed. Out of 100 offspring, how many are expected to be tall?
Answer: ______________
Two brown-eyed parents have a blue-eyed child. Priya says this is impossible because both parents have brown eyes. What's wrong with her reasoning?
- Blue eyes cannot be inherited, so the child must not be theirs
- Brown eyes are recessive, so this is expected
- Both parents could be Bb, each carrying a hidden recessive b allele

Answer key

For grown-ups. Fold this page away before handing over the rest.

Dominant · A dominant allele only needs one copy to show up in the body.
Alleles · Alleles are different versions of the same gene. You get one allele from each parent.
False · A recessive allele only shows up when both copies are the recessive version. One copy gets covered by a dominant allele.
3 · BB, Bb, and Bb all carry at least one B, so 3 out of 4 boxes show the dominant trait.
1 · Crossing Bb x Bb gives BB, Bb, Bb, bb. Only 1 of the 4 boxes is bb.
The combination of alleles she carries · Genotype is the pair of alleles a person carries. Phenotype is the trait you actually see.
75 · A Tt x Tt cross gives a 3:1 ratio, so about 75 out of 100 (3/4) are expected to be tall.
Both parents could be Bb, each carrying a hidden recessive b allele · A brown-eyed parent can still carry a hidden recessive allele. If both parents are Bb, about 1 in 4 children are expected to have blue eyes.