Question

use the pedigree to answer the following question. what is the genotype of individual iv-2?
options: bb, bb, not enough information given, bb

Explanation:

Step1: Analyze Pedigree Symbols

Blue symbols (filled) indicate affected individuals (recessive trait, as unaffected parents can have affected child). IV-2 is a white (unaffected) circle (female).

Step2: Determine Inheritance Pattern

The trait is recessive (since affected individuals have unaffected parents). For a recessive trait, unaffected individuals can be carriers (Bb) or homozygous dominant (BB). But IV-2's parent (III-4, male, white) and spouse (III-1, female, blue - affected, so genotype \( bb \)): their child (IV-1, blue - \( bb \)) means III-4 must be \( Bb \) (to pass \( b \)). Now, IV-2: her parents (III-4: \( Bb \); III-2: let's check lineage. Wait, IV-2's mother is III-2 (white), father III-4 (\( Bb \)). But also, IV-1 is \( bb \) (from III-4 \( Bb \) and III-1 \( bb \)). Now, IV-2 is unaffected. Let's see: if the trait is autosomal recessive, IV-2's genotype: her father is \( Bb \), mother (III-2) – let's trace back. Wait, maybe simpler: affected is \( bb \), so unaffected can be \( BB \) or \( Bb \), but since there's an affected sibling (IV-1, \( bb \)), father is \( Bb \), so mother (III-2) – wait, no, IV-2's parents are III-4 ( \( Bb \)) and III-2 (white, so \( B? \)). Wait, no, the pedigree: IV-1 is blue (affected, \( bb \)), so her parents are III-1 (blue, \( bb \)) and III-4 (white, so must be \( Bb \) to give \( b \)). Then IV-2 is the sister of IV-1, so her parents are III-4 (\( Bb \)) and III-2 (white, \( B? \)). But since IV-1 is \( bb \), father is \( Bb \), so mother (III-2) – wait, no, III-2 is married to III-4? Wait, the pedigree: III-4 (square, white) and III-2 (circle, white) are married? Wait, IV-1 is blue (female) with parents III-1 (blue, female) and III-4 (white, male). So III-4 is \( Bb \) (since he has a child \( bb \) with \( bb \) partner). Then IV-2 is the daughter of III-4 (\( Bb \)) and III-2 (white, female). Wait, maybe I misread. Wait, the pedigree: IV-1 (blue, female) is child of III-1 (blue, female) and III-4 (white, male). So III-4 is \( Bb \) (because he has a \( bb \) child with \( bb \) mother). Then IV-2 is the other child of III-4 and III-2? Wait, no, the circles and squares: III-4 (square, white) is married to III-2 (circle, white)? No, III-4 is married to III-1 (blue, circle)? Wait, no, the pedigree: III-1 (blue, circle) and III-4 (white, square) have IV-1 (blue, circle) and IV-2 (white, circle). Ah! There we go. So III-1 (blue, \( bb \)) and III-4 (white, \( Bb \)) have IV-1 ( \( bb \)) and IV-2 (white, so \( B? \)). Since III-1 is \( bb \), she can only give \( b \), so III-4 must give \( b \) to IV-1 ( \( bb \)), so III-4 is \( Bb \) (gives \( b \) to IV-1). Then IV-2: from III-1 ( \( bb \), gives \( b \)) and III-4 ( \( Bb \), can give \( B \) or \( b \)). Wait, no! Wait, IV-1 is \( bb \), so both parents must give \( b \). So III-1 is \( bb \) (gives \( b \)), III-4 must give \( b \), so III-4 is \( Bb \) (no, \( Bb \) can give \( B \) or \( b \)). Wait, no: if child is \( bb \), both parents must contribute \( b \). So III-1 is \( bb \) (contributes \( b \)), so III-4 must also contribute \( b \), so III-4 is \( bb \)? But III-4 is white (unaffected). Contradiction. So maybe the trait is dominant? No, dominant would mean affected parents have affected children. Wait, maybe the trait is autosomal recessive, and III-4 is \( Bb \), III-1 is \( bb \), so IV-1 is \( bb \) ( \( b \) from III-1, \( b \) from III-4). Then III-4 is \( Bb \) (so he has \( B \) and \( b \)). Then IV-2 is the child of III-4 (\( Bb \)) and III-1 (\( bb \))? No, IV-2 is a white circle, so unaffected. So IV-2's genotype: from III-1 (\( bb \), gives \( b \)) and III-4 (\( Bb \), gives \( B \) or \( b \)). If she's unaffected, she must have at least one \( B \). So possible genotypes: \( Bb \) (if father gives \( B \), mother \( b \)) or \( bb \) (but she's unaffected, so no). Wait, no: if mother is \( bb \) (III-1), father is \( Bb \), then children: \( Bb \) (unaffected) or \( bb \) (affected). So IV-1 is \( bb \) (affected), IV-2 is \( Bb \) (unaffected). Wait, that makes sense! Because father \( Bb \) (gives \( B \) to IV-2, \( b \) to IV-1) and mother \( bb \) (gives \( b \) to both). So IV-2 is \( Bb \). Wait, but the options are Bb, BB, bb, not enough. Wait, let's re-express:

- Affected (blue) is \( bb \) (recessive).
- III-1 (blue) is \( bb \).
- III-4 (white) has a child \( bb \) (IV-1), so III-4 must be \( Bb \) (since he gives \( b \) to IV-1, and is unaffected, so has \( B \)).
- IV-2 is the child of III-1 (\( bb \)) and III-4 (\( Bb \)).
- Possible genotypes for IV-2: \( Bb \) (from \( B \) of father and \( b \) of mother) or \( bb \) (from \( b \) of father and \( b \) of mother). But IV-2 is white (unaffected), so cannot be \( bb \). So must be \( Bb \).

Wait, but wait: if the trait is autosomal recessive, then \( bb \) is affected, \( Bb \) or \( BB \) is unaffected. So IV-2, being unaffected, and having a mother \( bb \) and father \( Bb \), can only be \( Bb \) (since mother can only give \( b \), father can give \( B \) or \( b \); if father gives \( b \), child is \( bb \) (affected), but IV-2 is unaffected, so father must have given \( B \), so genotype \( Bb \).

Step3: Eliminate Other Options

- \( BB \): Father is \( Bb \), so can't give \( B \) twice (mother is \( bb \), gives \( b \)). So \( BB \) is impossible.
- \( bb \): IV-2 is white (unaffected), so \( bb \) is wrong.
- Not enough info: But we have enough to deduce \( Bb \) (since affected sibling, father \( Bb \), mother \( bb \), so child must be \( Bb \) to be unaffected).

Answer:

Bb (the option with identifier, e.g., if the options are A. Bb, B. BB, C. bb, D. Not enough, then A. Bb)