Pedigree Worksheet Answer Key: Interpreting a Human Pedigree Chart.

Let’s go step by step to answer each question using the pedigree chart.

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Question 1: Males (squares)

In a pedigree, squares = males.
Darkened square = has hemophilia.
Clear square = normal blood clotting.

Look at all generations:

- Generation I: 1 male (square #1) → clear
- Generation II: 1 male (square next to circle #3) → clear
- Generation III: 2 males — one clear square, one dark square (#4 in row III)
- Generation IV: 5 males — let’s count squares: first is dark, third is dark, fifth and sixth are clear, seventh? Wait — let’s list them properly.

Actually, let’s count ALL squares in the entire chart:

Generation I:
→ Square #1 → 1 male

Generation II:
→ One square married to circle #3 → 1 male

Generation III:
→ Two squares: one on left (clear), one in middle (dark) → 2 males

Generation IV:
→ Look at bottom row:
Squares from left to right:
1st: dark square
2nd: circle (female)
3rd: dark square
4th: circle (female)
5th: clear square
6th: clear square
7th: circle (female)

Wait — that’s 4 squares in generation IV? Let me recount carefully.

Actually, looking again:

Row IV has 8 individuals total (as per answer key hint). Let’s label positions:

IV-1: dark square → male
IV-2: clear circle → female
IV-3: dark square → male
IV-4: dark circle → female
IV-5: clear square → male
IV-6: clear square → male
IV-7: clear circle → female
Wait — that’s only 7? But answer says 8 females and 8 males → total 16 people.

Let me count all symbols:

Generation I: 2 people → 1 square, 1 circle
Generation II: 3 people → 2 circles, 1 square
Generation III: 3 people → 2 squares, 1 circle? Wait no — actually:

Looking at structure:

I: [1]□ — ●[2]
II: [3]○ — ○ — □ (so 3 people: two females, one male)
III: □ — ○ — ■ — ○ (wait, no — actually, the parents in II have 3 children in III: left square, middle circle, right dark square — then the dark square marries an outside circle → so III has 4 people? No.

Better way: Count every symbol.

List all:

Gen I:
- I-1: square → male
- I-2: circle → female
Total: 1M, 1F

Gen II:
Children of I-1 & I-2:
- II-3: circle → female
- Another circle (unnumbered) → female
Then that second circle marries a square → so add 1 male
So Gen II: 2 females + 1 male = 3 people
But wait — the diagram shows: under I, line down to two circles (II-3 and another), then the other circle connects to a square → so yes, 3 in Gen II.

Gen III:
Children of II couple:
- Left: square → male
- Middle: circle → female
- Right: dark square → male
Then the dark square marries an outside circle → so add 1 female
So Gen III: 2 males + 2 females = 4 people? But usually we count only direct descendants unless specified.

Actually, standard pedigree counting: include everyone shown.

Let’s just count all squares and circles visually:

Squares (males):

- I-1
- II husband (married to II-3’s sister)
- III left child (square)
- III right child (dark square)
- IV-1 (dark square)
- IV-3 (dark square)
- IV-5 (clear square)
- IV-6 (clear square)

That’s 8 squares → 8 males ✔️

Now which are darkened (hemophiliac)?

- III right child (dark square)
- IV-1 (dark)
- IV-3 (dark)

That’s 3 males with hemophilia ✔️

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Question 2: Females (circles)

Circles = females
Darkened = hemophilia
Clear = normal

Count all circles:

Gen I: I-2 → 1
Gen II: II-3 and her sister → 2
Gen III: the wife of the dark square (outside marriage) → 1
Also, in Gen III, the middle child is a circle → 1 more? Wait.

From earlier:

Gen I: 1 female
Gen II: 2 females (the two daughters of I)
Gen III:
- The daughter of II couple (middle child) → 1
- The woman who married the dark square in III → 1
Gen IV:
- IV-2 (circle)
- IV-4 (dark circle)
- IV-7 (circle)
And also — in Gen IV, after IV-6 square, there’s another circle? Earlier I listed 7 in IV but should be 8 total per gen? Let's recount females.

List all circles:

1. I-2
2. II-3
3. II sister (married to square)
4. III middle child (daughter of II couple)
5. III wife (married to dark square)
6. IV-2
7. IV-4
8. IV-7

Yes, 8 females ✔️

Which are darkened?

- I-2 (top right, black circle)
- IV-4 (in bottom row, dark circle)

That’s 2 females with hemophilia ✔️

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Question 3: Marriages

Marriage = horizontal line connecting circle and square.

Find all such lines:

1. Between I-1 (square) and I-2 (circle) → marriage 1
2. Between II sister (circle) and her husband (square) → marriage 2
3. Between III dark square and his wife (circle) → marriage 3

No others — the children don’t show marriages. So 3 marriages ✔️

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Final Answer:

1a. 8
1b. 3
2a. 8
2b. 2
3a. 3