Question

Write down the last four digits of a telephone number. You will use these digits to represent the alleles in a gene. Odd digits will represent the allele for dimples, a dominate trait. Even digits will represent the allele for the recessive trait of no dimples. Count 0 as an even digit.

Use the first two digits in your number to represent a fathers genotype. Use the symbols D and d to write his genotype. Refer to the example in figure one
Use the last two digits of of your number to represent a mothers genotype.
Fathers genotype:
Mothers genotype:

Record the alleles that could be found in all the possible gametes that each parent could produce.
Fathers alleles:
Mothers alleles:

Use the punnett square to predict the genotype combinations for a cross between the mother and father. First enter the fathers possible alleles in the top row and the mothers possible alleles in the left column. Complete the square by combining the genotypes of the gametes.

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What are the possible genotypes for a person with dimples? for a person with no dimples?

What is the probability that a child will have dimples when both parents are heterozygous for the gene that determines dimples?

What is the probability that a child will have dimples when one parent is homozygous for the dimple allele and the other is heterozygous for that gene that determines dimples?

What is the probability that a child will have dimples when both parents are homozygous for the no dimple allele?

Which type of cross could have produced a 100% dimples among students in your class?

Answer 1

Let's use an example telephone number: **1234**.

**Fathers genotype:**
- Digits: 12
- The father has one odd digit (1) and one even digit (2).
- Genotype: **Dd** (where D = dimples, d = no dimples)

**Mothers genotype:**
- Digits: 34
- The mother has one odd digit (3) and one even digit (4).
- Genotype: **Dd** (where D = dimples, d = no dimples)

**Fathers alleles:**
- Possible gametes: **D, d**

**Mothers alleles:**
- Possible gametes: **D, d**

Let's set up the Punnett square:

```
D d
__________
D | DD | Dd |
|______|______|
d | Dd | dd |
|______|______|
```

**Possible Genotypes:**
- From the Punnett Square we see the possible genotypes:
- **DD** (homozygous dominant)
- **Dd** (heterozygous)
- **dd** (homozygous recessive)

**Possible genotypes for a person with dimples:**
- **DD** and **Dd** (as having at least one dominant allele D results in dimples)

**Possible genotypes for a person with no dimples:**
- **dd** (having no dominant allele results in no dimples)

**Probability that a child will have dimples when both parents are heterozygous for the gene that determines dimples:**
- From the Punnett Square, the combinations could be:
- 1/4 (DD), 1/2 (Dd), 0 (dd)
- Thus, the probability of having dimples (DD + Dd) = 3/4 or 75%.

**Probability that a child will have dimples when one parent is homozygous for the dimple allele and the other is heterozygous for that gene:**
- When one parent is **DD** and the other is **Dd**, the Punnett Square looks like this:

```
D D
__________
D | DD | DD |
|______|______|
d | Dd | Dd |
|______|______|
```

- The combinations are all dimples:
- 2 (DD) + 2 (Dd) = 100%
- The probability of having dimples = 1 (or 100%).

**Probability that a child will have dimples when both parents are homozygous for the no dimple allele:**
- If both parents are **dd**, then there's no possibility of producing a child with dimples.
- Punnett Square would look like this:

```
d d
__________
d | dd | dd |
|______|______|
d | dd | dd |
|______|______|
```

- Probability of having dimples = 0%.

**Which type of cross could have produced a 100% dimples among students in your class?**
- This would occur if both parents are homozygous dominant (DD). If both parents have the genotype **DD**, all offspring would inherit a D from each parent, resulting in 100% dimples.

**Overall Conclusion:**
- These genetic predictions reinforce how dominant and recessive traits interact and predict offspring phenotypes based on parental genotypes.