Analysis of three human pedigree charts illustrating the inheritance of attached earlobes, tongue rolling, and colorblindness, with questions about dominance and carrier status.

Here is the step-by-step solution to the pedigree problems.

Part A: Attached Earlobes

Step 1: Analyze the parents and offspring.
Look at the first generation ($P_1$) at the top left. There is a square (male) and a circle (female). Both are empty, which means they do not have attached earlobes (they have free earlobes).

Step 2: Look for the trait appearing in the children.
In the next generation ($F_1$), one of their sons (the filled-in square) does have attached earlobes.

Step 3: Determine Dominant vs. Recessive.
* If the trait were dominant, at least one parent would have to have it to pass it on. Since neither parent has it, but the child does, the trait cannot be dominant.
* This is the classic sign of a recessive trait. The parents are "carriers" (heterozygous). They both carry the gene for attached earlobes but don't show it because the free earlobe gene masks it. When they both passed the hidden gene to their son, he showed the trait.

Answer for A:
Is the trait dominant or recessive? Recessive
How do you know? Two parents without the trait produced a child with the trait. This only happens if the trait is recessive and both parents are carriers.

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Part B: Tongue Rolling

Step 1: Analyze the inheritance pattern.
Look at the pedigree. The trait appears in every single generation ($P_1$, $F_1$, $F_2$, $F_3$). It never skips a generation.

Step 2: Check specific families.
Look at the couple in generation $F_1$ on the right side (a filled circle and an empty square). They have children in $F_2$. Some have the trait, some don't.
More importantly, look at generation $F_2$ on the left. A mother with the trait and a father without the trait have children with the trait.

Step 3: Determine Dominant vs. Recessive.
* In recessive traits, you often see parents without the trait having a child with it (like in Part A). We do not see that here. Every person with the trait has at least one parent with the trait.
* Because the trait shows up in every generation and affected individuals always have an affected parent, this indicates a dominant trait. If it were recessive, we would likely see it skip generations or appear in children of unaffected parents.

Answer for B:
Is this trait dominant or recessive? Dominant
Explain: The trait appears in every generation and does not skip. Every individual with the trait has at least one parent who also has the trait.

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Part C: Colorblindness

Step 1: Determine Dominant vs. Recessive.
Look at generation $F_1$ on the right. There is a mother (empty circle) and a father (empty square) who both have normal vision. However, in generation $F_2$, they have a son (filled square) who is colorblind.
* Just like in Part A, when two unaffected parents have an affected child, the trait must be recessive. The parents carried the gene but didn't show it.

Step 2: Analyze the mother of the colorblind girl in $F_3$.
* Locate the colorblind girl in generation $F_3$ (the filled circle at the bottom right).
* Her parents are in generation $F_2$: A father who is colorblind (filled square) and a mother with normal vision (empty circle).
* Colorblindness is a sex-linked trait found on the X chromosome. Let's use $X^N$ for normal vision and $X^n$ for colorblindness.
* The girl is colorblind, so her genotype is $X^n X^n$. She must have received one $X^n$ from her dad and one $X^n$ from her mom.
* Her dad is colorblind ($X^n Y$), so he definitely gave her an $X^n$.
* Her mom has normal vision, so she has at least one $X^N$. But since she passed an $X^n$ to her daughter, her genotype must be $X^N X^n$.

Step 3: Conclusion about the mother.
Since the mother has the gene for colorblindness ($X^n$) but has normal vision herself ($X^N$), she is a carrier.

Answer for C:
Is this trait dominant or recessive? Recessive
Is the mother of the colorblind girl... carrier, or person with normal vision? A carrier
Explain: The trait is recessive because unaffected parents had an affected child. The mother of the colorblind girl must be a carrier because she has normal vision but passed the recessive colorblind gene to her daughter.

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Final Answer:

A.
* Recessive
* How do you know? Unaffected parents (in generation $P_1$) had an affected child (in generation $F_1$). This indicates the parents were carriers of a hidden recessive gene.

B.
* Dominant
* Explain: The trait appears in every generation and never skips. Every person with the trait has at least one parent with the trait.

C.
* Recessive
* Carrier
* Explain: The trait is recessive because unaffected parents produced an affected child. The mother of the colorblind girl is a carrier because she has normal vision but passed the recessive allele to her daughter (who needed two copies of the recessive gene to be colorblind).