**Core Concept**
Testicular feminization syndrome, also known as androgen insensitivity syndrome (AIS), is a rare genetic disorder where individuals with XY chromosomes are resistant to male hormones (androgens) and have female external genitalia.

**Why the Correct Answer is Right**
In individuals with AIS, the SRY gene on the Y chromosome triggers the development of testes, but the androgen receptors are non-functional, leading to the inability to respond to androgens. As a result, the individual develops female external genitalia, despite having testes. They often have a short vagina, a blind-ending uterine cavity, and rudimentary ovaries. The breast development is also affected, as the individual has a partial response to estrogen, leading to normal to enlarged breast size due to the peripheral conversion of androgens to estrogens.

**Why Each Wrong Option is Incorrect**
* **Option A:** A chromatin-positive buccal smear is characteristic of individuals with XX chromosomes (females), not those with AIS who have XY chromosomes.
* **Option C:** Menstruation is not observed in individuals with AIS, as they have testes and no uterus, but rather a blind-ending uterine cavity.
* **Option D:** Familial incidence is not recognized in AIS, as it is usually an X-linked recessive disorder, and the mutations are typically de novo.

**Clinical Pearl / High-Yield Fact**
AIS is a classic example of a condition where the phenotype (physical appearance) does not match the genotype (genetic makeup), highlighting the complex interactions between genetics, hormones, and development.

**Correct Answer:** B. Normal breast size is observed.