Question

The ability to taste the bitter chemical phenylthiocarbamide (PTC) is a dominant trait that can be passed from parent to child. If two heterozygous parents who can taste PTC have a child, what is the percent probability that their child can also taste PTC?

Answer 1

To determine the probability that a child of two heterozygous parents can taste the bitter chemical phenylthiocarbamide (PTC), we can use a Punnett square.

Let's denote the allele for tasting PTC as \( T \) (dominant) and the allele for not tasting PTC as \( t \) (recessive). Since both parents are heterozygous, their genotypes are \( Tt \).

Now, let's set up a Punnett square for the crosses:

```
T t
----------------
T | TT | Tt |
----------------
t | Tt | tt |
----------------
```

From the Punnett square, we can see the possible genotypes of the offspring:

- \( TT \): 1 (25% probability)
- \( Tt \): 2 (50% probability)
- \( tt \): 1 (25% probability)

Now, any genotype that includes at least one \( T \) (i.e., \( TT \) or \( Tt \)) will result in the ability to taste PTC. So we need to add the probabilities of the genotypes that can taste PTC:

- \( TT \): 25%
- \( Tt \): 50%

To find the total probability of tasting PTC:

\[
25\% + 50\% = 75\%
\]

Thus, the probability that their child can taste PTC is **75%**.