Question

pedigrees

1. both of the pedigrees below show the sex - linked trait hemophilia. shaded individuals who are affected.

(first pedigree with x - linked recessive label and related questions: how can you tell that this is a sex - linked trait? note how many are males. how does someone inherit the trait? is it from the mother or the father? second pedigree with i₁, i₂, ii₁, ii₂, ii₃, iii₁, iii₂, iii₃, iii₄ and question: this pedigree actually shows many females affected. what must be the genotype of individual ii2?)

1. the pedigrees below show a recessive trait like detached earlobes. this is not a sex - linked trait.

(first pedigree with a, b, c labels and related questions: how can you tell these pedigrees show a recessive trait? what is the genotype of person a? what is the genotype of person b? what is the genotype of person c? second pedigree with father, mother, todd, justin, you, jane and legend: diagnosis = known carrier, diagnosis = affected, labeled figure 1)

Explanation:

To determine if a pedigree shows a recessive trait, we look for patterns where affected individuals (shaded) have unaffected parents (who are carriers). In autosomal recessive inheritance, carriers (heterozygotes) don't show the trait but can pass it on. For the genotype questions:

• Person A: Since A is shaded (affected), and the trait is recessive (let's assume allele \( a \) for recessive, \( A \) for dominant), an affected individual must be \( aa \) (homozygous recessive) because recessive traits are only expressed when both alleles are recessive.
• Person B: B is unshaded (unaffected) but has a child (or offspring) in the pedigree? Wait, looking at the first autosomal recessive pedigree (A and B’s family), B is a square (male) unshaded. Since A is \( aa \) (affected), and their children (like the first generation under A and B) include unshaded individuals, B must be \( Aa \) (heterozygous carrier) to pass on the recessive allele (because if B were \( AA \), all children would be \( Aa \) or \( AA \), but wait—no, A is \( aa \), so children would get \( a \) from A and either \( A \) or \( a \) from B. Wait, maybe I misread. Wait, the trait is recessive (detached earlobes, autosomal recessive). So affected is \( aa \), carrier is \( Aa \), unaffected non - carrier is \( AA \).

Person A: shaded (affected) → \( aa \).
Person B: unshaded, and since A is \( aa \), and their children (the first row under A and B: a square, a circle, a square) — wait, the first child of A (shaded female) and B (unshaded male) is a square (unshaded). So A is \( aa \), so she gives \( a \) to all children. B, to have a child with A, if the child is unshaded, the child must be \( Aa \) (since \( a \) from A and \( A \) from B). So B must be \( Aa \) (because \( Aa \times aa \) gives \( Aa \) (unaffected, carrier) and \( aa \) (affected). Wait, but in the pedigree, do they have an affected child? Wait, the bottom row has shaded individuals (affected), so those must be \( aa \). So their parents (the middle row, like the square and circle that have the bottom - row children) must be carriers (\( Aa \)). Going back to A and B: A is \( aa \) (affected), B is \( Aa \) (carrier) because he can pass the \( a \) allele to some children (the affected ones in later generations).
Person C: C is a square (male) unshaded. Looking at C’s position: he is in the second generation (under A and B’s children). Wait, C is in the row with a square, circle, square (children of A and B). Wait, no—maybe C is in the third generation? Wait, the pedigree: A (shaded female) and B (unshaded male) have children: square, circle, square. Then one of those squares (C?) marries a circle, and they have children: square, circle, circle. Then one of those squares marries a circle, and they have children: shaded square, square, shaded circle, square. So C: unshaded, and since he has an affected child (shaded square or circle), he must be a carrier (\( Aa \)), because to have an \( aa \) child, both parents must contribute \( a \). So C is \( Aa \).

Answer:

• How can you tell these pedigrees show a recessive trait?

Unaffected parents (carriers, heterozygotes) have affected children (homozygous recessive), and affected individuals (shaded) have two recessive alleles.

• Genotype of person A: \( aa \)
• Genotype of person B: \( Aa \)
• Genotype of person C: \( Aa \)