Big foreheads(F) are dominant to little foreheads. A woman with a small
forehead marries a man with a big forehead. What is the probability the man
and woman’s children will have big foreheads? What is the probability of little
foreheads? Hint-you need to do two Punnett squares.
The Correct Answer and Explanation is :
To solve this genetics problem, we need to use Punnett squares to determine the probabilities of the offspring inheriting big or small foreheads. Here’s the step-by-step explanation:
Step 1: Understand the Genetics
- Big foreheads (F) are dominant.
- Little foreheads (f) are recessive.
- The woman has a small forehead, so her genotype must be ff.
- The man has a big forehead, so his genotype could be either FF (homozygous dominant) or Ff (heterozygous dominant). We don’t know his exact genotype, so we will consider both possibilities.
Step 2: Punnett Square 1 (Woman: ff, Man: Ff)
First, let’s assume the man is heterozygous (Ff). This is a common scenario, as most people with a big forehead have the genotype Ff.
- Woman’s genotype: ff
- Man’s genotype: Ff
The Punnett square for this cross would look like this:
| F | f | |
|---|---|---|
| f | Ff | ff |
| f | Ff | ff |
Results:
- 50% of the offspring (Ff) will have big foreheads (since F is dominant).
- 50% of the offspring (ff) will have little foreheads (since both alleles are recessive).
Probability of Big Forehead: 50%
Probability of Little Forehead: 50%
Step 3: Punnett Square 2 (Woman: ff, Man: FF)
Now, let’s assume the man is homozygous dominant (FF).
- Woman’s genotype: ff
- Man’s genotype: FF
The Punnett square for this cross would look like this:
| F | F | |
|---|---|---|
| f | Ff | Ff |
| f | Ff | Ff |
Results:
- 100% of the offspring (Ff) will have big foreheads.
Probability of Big Forehead: 100%
Probability of Little Forehead: 0%
Conclusion:
- If the man is heterozygous (Ff), there’s a 50% chance the children will have big foreheads and a 50% chance they’ll have little foreheads.
- If the man is homozygous dominant (FF), all the children will have big foreheads, with no chance for little foreheads.
Thus, the probabilities depend on the father’s genotype, but the general range is a 50% chance of big foreheads and 50% chance of little foreheads if the man is heterozygous.