Final Answer:
A. Recessive — because two parents without the trait (free earlobes) had a child with the trait (attached earlobes).
B. Dominant — because the trait appears in every generation and affected parents can have unaffected children.
C. Recessive — because it skips generations and mostly affects males; the mother of the colorblind girl is a carrier.
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Explanation:
Let’s go one by one.
A. Attached earlobes:
Look at the first generation (P₁). Both parents are squares and circles with no shading — meaning they don’t have attached earlobes. But one of their kids (in F₁) is a shaded square — that means he has attached earlobes.
If two parents without a trait have a child with the trait, that trait must be recessive. Because for a recessive trait to show up, both parents must carry the hidden gene.
B. Tongue rolling:
This trait shows up in every generation. That’s a big clue it’s dominant. Also, some parents who can roll their tongues have kids who can’t — that’s possible only if the trait is dominant. If it were recessive, you’d need both parents to have the trait to pass it on — but here, even when one parent doesn’t have it, kids still get it sometimes. So it’s dominant.
C. Colorblindness:
This is sex-linked — usually carried on the X chromosome. Males (XY) only need one copy to be colorblind. Females (XX) need two copies.
In F₃, there’s a colorblind girl. That means she got the gene from both parents. Her father is colorblind (he gave her his X with the gene), and her mother must have given her the other X with the gene too — so the mom is a carrier (she has one normal X and one bad X, but doesn’t show the trait).
Also, the trait skips generations — that’s typical of recessive traits.
So:
- A = Recessive
- B = Dominant
- C = Recessive, and the mom is a carrier.
Parent Tip: Review the logic above to help your child master the concept of pedigree worksheet biology.
