**Question:** An Rh-negative woman married to a heterozygous Rh-positive man has three children. The probability that all three of their children are Rh-positive is: Himachal 10

**Core Concept:** Probability, Punnett Squares, and Genetic Inheritance

In this question, we are dealing with the inheritance of the Rh factor, a blood group antigen, which is determined by the presence or absence of the Rh gene. In humans, the Rh gene is located on chromosome 1. An individual is considered to have the Rh-negative blood type if they lack the Rh gene (homozygous, RR) or possess one normal (R+) and one abnormal (r-) allele (heterozygous, Rr). The Rh-positive blood type is determined by having two normal alleles (RR or Rr).

**Why the Correct Answer is Right:**

The correct answer, **D** (0.0001), represents the probability of all three children inheriting the Rh-positive allele from their heterozygous father (Rr) and homozygous Rh-positive allele from their Rh-negative mother (RR).

To determine this probability, we can use Punnett Squares to visualize the possible combinations of Rh genotypes:


In the Punnett Square above, the possible genotypes are:
1. Homozygous Rh-negative (RR)
2. Heterozygous Rh-positive (Rr)
3. Homozygous Rh-positive (RR)

**Why Each Wrong Option is Incorrect:**

A. Punnett Square:
```
Rr rr
+-----+-----+
| | |
+-----+-----+
| RR | Rr |
+-----+-----+
```
Option A (0.0004) represents the probability that all three children inherit the Rr allele from their heterozygous father, but the mother is Rh-negative (RR), which is incorrect.

B. Punnett Square:
```
Rr rr
+-----+-----+
| | |
+-----+-----+
| Rr | Rr |
+-----+-----+
```
Option B (0.0003) represents the probability that all three children inherit the Rr allele from their heterozygous father, but the mother is Rh-negative (RR), which is incorrect.

C. Punnett Square:
```
Rr rr
+-----+-----+
| | |