Pedigree chart showing the inheritance of hemophilia, a sex-linked recessive condition, with questions to determine genotypes and inheritance patterns.

Let’s go step by step through the pedigree and answer each question carefully.

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First, let’s understand the symbols:

- Square = male
- Circle = female
- Filled (dark) shape = has hemophilia (recessive trait, sex-linked on X chromosome)
- Open shape = normal (does not have hemophilia)
- Horizontal line between square and circle = marriage
- Vertical line down from marriage = children
- Generations are labeled I, II, III, IV from top to bottom

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Question 1: Number all individuals at the top of each shape.

We’ll number them left to right in each generation:

Generation I:
→ Male #1 (open square)
→ Female #2 (filled circle)

Generation II:
→ Female #3 (open circle) — child of I-1 and I-2
→ Another female (open circle) — also child of I-1 and I-2 → let’s call her #4
→ Her husband (open square) → #5

Generation III:
→ First child: open square → #6
→ Second: open circle → #7
→ Third: filled square → #8
→ His wife: open circle → #9

Generation IV:
→ First child: filled square → #10
→ Second: open circle → #11
→ Third: filled square → #12
→ Fourth: filled circle → #13
→ Fifth: open square → #14
→ Sixth: open square → #15
→ Seventh: open circle → #16

*(Note: The actual numbering isn’t required for answers unless specified, but we use it internally to count.)*

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Question 2: Males (squares)

Look at all squares:

Gen I: 1 male (#1)
Gen II: 1 male (#5)
Gen III: 2 males (#6, #8)
Gen IV: 4 males (#10, #12, #14, #15)

Total males = 1 + 1 + 2 + 4 = 8

Now, how many males have hemophilia? Look for filled squares:

Gen I: none
Gen II: none
Gen III: #8 (filled) → 1
Gen IV: #10, #12 → 2 more

Total males with hemophilia = 1 + 2 = 3

✔ Answer 2a: 8
✔ Answer 2b: 3

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Question 3: Females (circles)

Count all circles:

Gen I: 1 female (#2)
Gen II: 2 females (#3, #4)
Gen III: 2 females (#7, #9)
Gen IV: 3 females (#11, #13, #16)

Total females = 1 + 2 + 2 + 3 = 8

Females with hemophilia? Only filled circles.

Only one: Gen IV, #13 (filled circle)

✔ Answer 3a: 8
✔ Answer 3b: 1

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Question 4: Marriages (horizontal lines connecting circle and square)

Look for horizontal lines between a male and female:

- Gen I: #1 and #2 → 1 marriage
- Gen II: #4 and #5 → 1 marriage
- Gen III: #8 and #9 → 1 marriage

Total marriages = 3

✔ Answer 4a: 3

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Question 5: Children per couple

a. Couple in row I: #1 and #2 → they have two daughters in Gen II: #3 and #4 → so 2 children

b. Couple in row II: #4 and #5 → their children are in Gen III: #6, #7, #8 → that’s 3 children

✔ Answer 5a: 2
✔ Answer 5b: 3

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Question 6: Generations and members

a. How many generations? Labeled I, II, III, IV → 4 generations

b. Members in fourth generation (Gen IV): We counted 7 individuals: #10 to #16 → 7 members

✔ Answer 6a: 4
✔ Answer 6b: 7

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Question 7: Genotypes for males (sex-linked: XY or XⁿY)

Remember:
- Normal male = XᴺY (N = dominant normal allele)
- Hemophiliac male = XⁿY (n = recessive disease allele)

a. Individual #1 (Gen I, open square) → normal → genotype: XᴺY, phenotype: normal

b. Individual #10 (Gen IV, filled square) → has hemophilia → genotype: XⁿY, phenotype: hemophilia

c. First born male in Gen III → that’s #6 (open square) → normal → genotype: XᴺY, phenotype: normal

✔ Answer 7a: Genotype: XᴺY, Phenotype: normal
✔ Answer 7b: Genotype: XⁿY, Phenotype: hemophilia
✔ Answer 7c: Genotype: XᴺY, Phenotype: normal

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Question 8: Females with hemophilia

Hemophilia is recessive and X-linked → females need TWO recessive alleles to show it → genotype must be XⁿXⁿ

How many such females? Only one: Gen IV, #13 (filled circle)

✔ Answer 8a: 1

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Question 9: Female who marries into family in Gen III → that’s #9 (wife of #8)

She is an open circle → does NOT have hemophilia.

But she has children with hemophilia:

- Son #10: XⁿY → got Y from dad (#8), so got Xⁿ from mom → so mom must have given Xⁿ
- Daughter #13: XⁿXⁿ → got one Xⁿ from dad (#8 → he is XⁿY, so gives Xⁿ to daughters), and one Xⁿ from mom → so mom gave Xⁿ again

So this female (#9) must carry at least one Xⁿ.

But she herself is normal → so she must be heterozygous: XᴺXⁿ

Why? Because if she were XⁿXⁿ, she’d have hemophilia (but she doesn’t). If she were XᴺX, she couldn’t give Xⁿ to any child — but she did.

So she’s a carrier: XᴺXⁿ

✔ Answer 9a: XᴺXⁿ
✔ Answer 9b: She has children with hemophilia (sons and a daughter), which means she must have passed on the recessive allele (Xⁿ). Since she doesn’t have the disease herself, she must have one normal allele (Xᴺ) and one recessive (Xⁿ) → making her a carrier.

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## Final Answer:

2a. 8
2b. 3
3a. 8
3b. 1
4a. 3
5a. 2
5b. 3
6a. 4
6b. 7
7a. Genotype: XᴺY, Phenotype: normal
7b. Genotype: XⁿY, Phenotype: hemophilia
7c. Genotype: XᴺY, Phenotype: normal
8a. 1
9a. XᴺXⁿ
9b. She has children with hemophilia, meaning she passed on the recessive allele (Xⁿ). Since she does not have hemophilia herself, she must be heterozygous (carrier): XᴺXⁿ