B-4.7 - Genetics Worksheet - Inheritance Patterns - Free Printable

Let’s go through each question one by one, step by step.

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Question 1:

We’re crossing two organisms with genotypes R’R and RR.

The key says:
- RR = Red
- R’R = Pink
- R’R’ = White

This is a case where the heterozygote (R’R) shows a blend of the two homozygotes — red and white make pink. That’s called incomplete dominance.

Now let’s fill in the Punnett square:

Parent 1 (top): R and R
Parent 2 (side): R’ and R’

So the four boxes will be:
- Top-left: R’ + R → R’R
- Top-right: R’ + R → R’R
- Bottom-left: R’ + R → R’R
- Bottom-right: R’ + R → R’R

All offspring are R’R → which means all are Pink.

So:
- Type of Inheritance: Incomplete Dominance
- Genotype: All R’R
- Phenotype: All Pink

✔ Checked: Yes, all combinations give R’R. No mistakes.

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Question 2:

Cross between B and W alleles.

Key:
- BB = Black
- WW = White
- BW = Speckled

Here, when you have both alleles (BW), you see BOTH colors — speckled. That’s not blending — it’s showing both traits at once. That’s called codominance.

Punnett square:

Parent 1 (top): B and B
Parent 2 (side): W and W

Offspring:
- All four boxes: B + W → BW

So all offspring are BW → Speckled.

Therefore:
- Type of Inheritance: Codominance
- Genotype: All BW
- Phenotype: All Speckled

✔ Checked: Correct. Codominance because both traits appear together.

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Question 3:

Hemophilia is an X-linked recessive trait. The notation uses X^H (normal) and X^h (hemophilia allele). Y chromosome doesn’t carry the gene.

Given Punnett square setup:

Father’s gametes: X^h and Y
Mother’s gametes: X^H and X^h

Wait — actually, looking at the square:

Top row (father’s contribution): X^h and Y
Left column (mother’s contribution): X^H and X^h

That means:
- Mother must be X^H X^h (she can give either X^H or X^h)
- Father must be X^h Y (he gives X^h or Y)

But wait — if father gives X^h, that would mean he has hemophilia? Let’s check.

Actually, in standard notation for X-linked traits:

- Males are XY. If they have the disease allele on their X, they show it.
- Females are XX. They need two copies to show the disease; one copy makes them carriers.

In this square:

Father’s gametes: X^h and Y → so his genotype is X^h Y → he HAS hemophilia.

Mother’s gametes: X^H and X^h → her genotype is X^H X^h → she is a carrier (does NOT have hemophilia).

Now fill the square:

Top-left: Mother’s X^H + Father’s X^h → daughter: X^H X^h → carrier, no disease
Top-right: Mother’s X^H + Father’s Y → son: X^H Y → normal
Bottom-left: Mother’s X^h + Father’s X^h → daughter: X^h X^h → HAS hemophilia
Bottom-right: Mother’s X^h + Father’s Y → son: X^h Y → HAS hemophilia

So now answer the questions:

a. Mother’s genotype? → X^H X^h
b. Father’s phenotype? → He has hemophilia (since he’s X^h Y)
c. Is it possible for daughters to have hemophilia? → YES (bottom-left: X^h X^h)
d. Is it possible for daughters to be carriers? → YES (top-left: X^H X^h)
e. Is it possible for sons to have hemophilia? → YES (bottom-right: X^h Y)
f. Is it possible for sons to be carriers? → NO. Sons get Y from dad and X from mom. If they get X^h, they HAVE the disease. There’s no “carrier” state for males in X-linked recessive — they either have it or don’t.
g. Chance (%) of having a child with hemophilia? → Out of 4 children:
- Daughter with hemophilia: 1
- Son with hemophilia: 1
→ Total 2 out of 4 = 50%
h. What type of inheritance? → X-linked recessive

✔ Double-checked: All answers match the Punnett square results.

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Question 4:

Pedigree chart:

Generation I: Female affected (filled circle), male unaffected (open square)
They have 4 children in Generation II:
- Male unaffected
- Female affected
- Male unaffected
- Female affected

Then, one of the affected females (II-2) has children with an unaffected male:
- One unaffected son
- One affected daughter

What pattern is this?

Look: Affected mother passes to some sons and some daughters. Unaffected father doesn’t pass it to anyone (which makes sense if it’s dominant — he doesn’t have the allele).

Also, every affected person has at least one affected parent — except possibly if new mutation, but here it looks consistent.

In Generation I, mom is affected, dad is not. Some kids are affected, some aren’t → suggests it’s not recessive (because if it were recessive, unaffected dad would have to be carrier, but then why are only half affected?).

Actually, if it’s autosomal dominant, then:

- Affected individuals have at least one copy of the dominant allele.
- Unaffected individuals are homozygous recessive.
- An affected parent (heterozygous) crossed with unaffected (homozygous recessive) should give ~50% affected offspring — which matches what we see.

Also, males and females are equally affected → not sex-linked.

And it appears in every generation → typical of dominant traits.

So: Autosomal Dominant

✔ Confirmed: Pattern fits autosomal dominant inheritance.

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Final Answer:

1. Type of Inheritance: Incomplete Dominance
Genotype: All R’R
Phenotype: All Pink

2. Type of Inheritance: Codominance
Genotype: All BW
Phenotype: All Speckled

3.
a. X^H X^h
b. Has hemophilia
c. Yes
d. Yes
e. Yes
f. No
g. 50%
h. X-linked recessive

4. Autosomal Dominant