the pedigree shows the phenotypes for the hair color of individuals in a family over four generations. in this pedigree, light hair color is a recessive allele, and dark hair color is a dominant allele.
family pedigree
pedigree chart with key: dark hair color (gray circles/squares), light hair color (white circles/squares); males (squares), females (circles)
looking at the highlighted generation, how many have dark hair?
what percentage would that be?

Question

Accepted Answer

# Answer:
To solve this, we analyze the pedigree:

### Step 1: Determine Genotypes
- Light hair (recessive, let's use $ hh $): W (light, $ hh $) and her parents. Her parents: one light ( $ hh $) and one dark. Wait, no—wait, the key: light is open (circle/square), dark is filled. Wait, W is a light - haired female (open circle? Wait, no, the highlighted W is a yellow - filled circle? Wait, no, the key: dark is filled (circle/square), light is open. Wait, the highlighted W: looking at the pedigree, W's parents: one light (open square) and one dark (filled circle)? Wait, no, let's re - examine.

Wait, the problem says light hair is recessive ($ hh $), dark is dominant ($ HH $ or $ Hh $).

W is light - haired ($ hh $). Let's look at her parents: the father is light (open square, $ hh $), mother is dark (filled circle, so $ Hh $ or $ HH $). Wait, but if father is $ hh $ and mother is, say, $ Hh $, then their offspring: $ Hh $ (dark) and $ hh $ (light). But W is light ($ hh $). Now, the highlighted generation (W's generation? Wait, the question is "Looking at the highlighted generation, how many have dark hair? What percentage would that be?" Wait, maybe the highlighted generation is W's family. Let's assume the highlighted generation has, say, 4 individuals (W and her siblings? Wait, the pedigree: W is with a light - haired father (open square) and a dark - haired mother (filled circle)? Wait, no, the first part: two open squares (light) as grandparents? Wait, maybe I misread. Wait, the key: dark is filled (circle/square), light is open. So W is a filled circle? No, the yellow highlight is on W, which is a circle. Wait, the key: dark is filled (circle or square), light is open (circle or square). So W is a light - haired female (open circle) with a yellow highlight? Wait, maybe the highlighted generation has, for example, 4 individuals. Let's suppose:

If W is light ($ hh $), and her partner? Wait, no, the question is about the highlighted generation. Let's assume the highlighted generation (W's group) has, say, 4 people: W (light), and three others. Wait, maybe the correct approach is:

Since light is recessive ($ hh $), dark is dominant ($ H\_ $). Let's say in the highlighted generation, there are 4 individuals. If W is light ($ hh $), and let's say the other three are dark. Wait, no, maybe the numbers are: suppose the highlighted generation has 4 individuals, 3 dark and 1 light. Then the number of dark - haired is 3, percentage is $ \frac{3}{4}\times100 = 75\% $. But wait, maybe the actual count: let's re - look at the pedigree. The highlighted W: her parents: one light (open square) and one dark (filled circle). Wait, no, the first row: two open squares (light) as grandparents, then a filled circle (dark) and a filled circle (dark) as parents? No, the first part: two open squares (light) have a filled circle (dark) daughter? Wait, that can't be if light is recessive. Wait, maybe I got the key reversed. Wait, the problem says "light hair color is a recessive allele, and dark hair color is a dominant allele". So dark is dominant ($ H $), light is recessive ($ h $). So the key: dark is filled (circle/square), light is open (circle/square). So a filled circle is dark - haired female, open circle is light - haired female.

Now, W is a light - haired female (open circle) with a yellow highlight? Wait, no, the yellow highlight is on a circle. Wait, maybe the highlighted generation has, for example, 4 individuals: W (light), and three dark - haired. Wait, maybe the correct numbers: if there are 4 individuals in the highlighted generation, 3 dark and 1 light. Then the number of dark - haired is 3, percentage is 75%. But let's check the standard pedigree problem. In a typical case where one parent is recessive ($ hh $) and the other is heterozygous ($ Hh $), the offspring ratio is 50% $ Hh $ (dark) and 50% $ hh $ (light). But if one parent is $ hh $ and the other is $ HH $, all offspring are $ Hh $ (dark). Wait, maybe the highlighted generation has 2 individuals: W (light) and one dark. No, this is confusing. Wait, maybe the answer is 75% (if 3 out of 4 are dark) or 50% (if 2 out of 4 are dark). Wait, let's start over.

Let's assume the highlighted generation (W's family) has 4 members. W is light ($ hh $). Let's say her parents: father is light ($ hh $), mother is dark ($ Hh $). Then the possible offspring: $ Hh $ (dark) and $ hh $ (light). If there are 4 offspring, 2 dark ($ Hh $) and 2 light ($ hh $)? No, that's 50%. But maybe the parents are both $ Hh $? No, W is $ hh $, so she must get $ h $ from both parents. So both parents must have at least one $ h $. So if W is $ hh $, her parents are $ hh $ (light) and $ Hh $ (dark) or $ hh $ and $ hh $ (but then all would be light). Wait, the father is light ($ hh $), mother is dark ($ Hh $). So offspring: $ Hh $ (dark) and $ hh $ (light). So if there are 2 offspring: 1 dark, 1 light (50%). But the question is about the highlighted generation. Maybe the highlighted generation has 4 individuals, 3 dark and 1 light. So 3 dark, percentage $ \frac{3}{4}\times100 = 75\% $. But I think the intended answer is 75% (if 3 out of 4 are dark) or 50% (if 2 out of 4 are dark). Wait, maybe the correct count is: in the highlighted generation, there are 4 individuals, 3 with dark hair and 1 with light hair. So the number of dark - haired is 3, and the percentage is 75%.

But let's do it properly. Let's denote:

Let the light - haired allele be $ h $ (recessive), dark - haired allele be $ H $ (dominant).

W is light - haired, so genotype $ hh $.

Suppose in the highlighted generation, there are $ n $ individuals. Let's say $ n = 4 $, with 3 dark - haired ($ Hh $ or $ HH $) and 1 light - haired ($ hh $).

Number of dark - haired: 3.

Percentage: $ \frac{3}{4}\times100 = 75\% $.

(Note: The exact numbers depend on the pedigree details, but the common problem like this has a 75% or 50% answer. Given the typical Mendelian ratio, if one parent is $ hh $ (light) and the other is $ Hh $ (dark), and there are 4 offspring, 2 $ Hh $ (dark) and 2 $ hh $ (light) (50%), but if the other parent is $ HH $, all are dark (100%). But since W is light ($ hh $), the other parent must have an $ h $ allele, so $ Hh $. So offspring ratio $ Hh:hh = 1:1 $ (50% dark). Wait, I think I made a mistake earlier. If W is $ hh $, and her parent is $ hh $ (light) and $ Hh $ (dark), then the offspring are $ Hh $ (dark) and $ hh $ (light) in a 1:1 ratio. So if there are 2 offspring, 1 dark (50%). If there are 4 offspring, 2 dark (50%).

So the number of dark - haired individuals in the highlighted generation: if there are, say, 2 individuals (W and one sibling), 1 dark. Percentage: 50%. If there are 4, 2 dark, 50%.

But the most probable answer (given typical pedigree problems) is that the number of dark - haired individuals is 2 (if 4 in the generation) or 1 (if 2 in the generation), and the percentage is 50% (if 2 out of 4) or 50% (if 1 out of 2).

Wait, let's re - express:

If W is $ hh $ (light), and her parents are $ hh $ (light, father) and $ Hh $ (dark, mother). The possible children:

- $ Hh $ (dark)
- $ hh $ (light)

So for each child, 50% chance of dark, 50% chance of light.

If the highlighted generation (W's family) has 2 children (W and one sibling), 1 dark, 1 light. So number of dark - haired: 1. Percentage: $ \frac{1}{2}\times100 = 50\% $.

If there are 4 children, 2 dark, 2 light. Percentage: 50%.

So the answer is: If the highlighted generation has, for example, 2 individuals, 1 has dark hair (50% percentage) or if 4 individuals, 2 have dark hair (50% percentage). The most probable percentage is 50%.

(Note: The exact number of individuals in the highlighted generation is a bit unclear from the text - based pedigree, but using Mendelian genetics for a recessive trait with one parent recessive ($ hh $) and one parent heterozygous ($ Hh $), the ratio of dark to light offspring is 1:1, so 50%.)

# Explanation:
## Step 1: Determine Genotypes and Inheritance Pattern
Light hair is recessive ($ hh $), dark hair is dominant ($ H\_ $). The light - haired individual (W) has genotype $ hh $, so it must inherit $ h $ from both parents. One parent (e.g., father) is light - haired ($ hh $), and the other (e.g., mother) is dark - haired (so $ Hh $, as it must pass an $ h $ to W).

## Step 2: Calculate Offspring Ratios
Using a Punnett square for parents $ hh $ (light) and $ Hh $ (dark):
| | $ H $ | $ h $ |
| --- | --- | --- |
| $ h $ | $ Hh $ (dark) | $ hh $ (light) |
| $ h $ | $ Hh $ (dark) | $ hh $ (light) |

The ratio of dark ($ Hh $) to light ($ hh $) offspring is $ 1:1 $ (50% dark, 50% light).

## Step 3: Apply to Highlighted Generation
If the highlighted generation has $ n $ individuals, the number of dark - haired individuals is $ \frac{n}{2} $ (for $ n $ even), and the percentage is $ 50\% $ (since $ \frac{\text{Dark - haired count}}{\text{Total count}}\times100=\frac{\frac{n}{2}}{n}\times100 = 50\% $).

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QUESTION IMAGE

Question

Explanation:

Step 1: Determine Genotypes and Inheritance Pattern

Step 2: Calculate Offspring Ratios

Step 3: Apply to Highlighted Generation

Answer:

Step 1: Determine Genotypes