Genetics worksheet on dog coat color inheritance using Punnett squares.

Let’s solve this step by step.

We are told:
- There is a hereditary deafness caused by a recessive gene “d”.
- That means:
→ To be deaf, the dog must have genotype dd (two copies of the recessive allele).
→ If the dog has at least one D, it can hear (genotypes DD or Dd).
- Gilbert is a male dog who can hear → so his genotype is either DD or Dd.
- We want to find out what his genotype is — specifically, whether he carries the deafness gene (i.e., is Dd) or not (DD).
- The way to test this is to breed him with a deaf female → which must be dd (since deafness is recessive).

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Part 1: What are the two possible genotypes of Gilbert?

Since Gilbert can hear, and deafness is recessive, he could be:

→ DD (homozygous dominant — no deafness gene)
→ Dd (heterozygous — carrier of deafness gene but still hears)

✔ So answer for part 1: DD or Dd

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Part 2: Breeding Gilbert with a deaf female (dd)

We’ll do two Punnett squares — one assuming Gilbert is DD, one assuming he is Dd.

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#### Possible Cross 1: Gilbert = DD × Deaf Female = dd

Gametes from Gilbert (DD): only D
Gametes from female (dd): only d

Punnett Square:

| | d | d |
|-------|-------|-------|
| D | Dd | Dd |
| D | Dd | Dd |

All offspring: Dd → all can hear (because they have one D)

So:

- % of possible Genotypes:
→ 100% Dd
→ 0% DD
→ 0% dd

- % of possible Phenotypes:
→ 100% Can Hear
→ 0% Deaf

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#### Possible Cross 2: Gilbert = Dd × Deaf Female = dd

Gametes from Gilbert (Dd): D or d
Gametes from female (dd): only d

Punnett Square:

| | d | d |
|-------|-------|-------|
| D | Dd | Dd |
| d | dd | dd |

Offspring:

- 50% Dd → can hear
- 50% dd → deaf

So:

- % of possible Genotypes:
→ 50% Dd
→ 0% DD
→ 50% dd

- % of possible Phenotypes:
→ 50% Can Hear
→ 50% Deaf

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Part 3: How would you tell the genotype of Gilbert’s male dog?

If we breed Gilbert with a deaf female (dd), then:

→ If any puppies are deaf (dd), that means Gilbert must have given them a “d” allele → so Gilbert is Dd.

→ If all puppies can hear (all Dd), then Gilbert likely gave only “D” alleles → so Gilbert is probably DD.

But note: even if Gilbert is Dd, there’s a 50% chance each puppy is hearing — so if you get only hearing puppies in a small litter, it might just be luck. But if you get *any* deaf puppy, you know for sure Gilbert is Dd.

So the key is:
👉 If any offspring are deaf, Gilbert is Dd. If all offspring can hear, Gilbert is likely DD.

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Final Answer:

1. Two possible genotypes of Gilbert: DD or Dd

2.
Possible Cross 1 (Gilbert = DD):
- % Genotypes: 100% Dd, 0% DD, 0% dd
- % Phenotypes: 100% Can Hear, 0% Deaf

Possible Cross 2 (Gilbert = Dd):
- % Genotypes: 50% Dd, 0% DD, 50% dd
- % Phenotypes: 50% Can Hear, 50% Deaf

3. You can tell Gilbert’s genotype by breeding him with a deaf female (dd). If any puppies are deaf, Gilbert is Dd. If all puppies can hear, Gilbert is likely DD.