**Core Concept**
Down's Syndrome, also known as Trisomy 21, is a genetic disorder caused by the presence of an extra copy of chromosome 21. This condition is characterized by distinct physical features, developmental delays, and an increased risk of certain medical complications.

**Why the Correct Answer is Right**
Down's Syndrome is a chromosomal disorder that affects both males and females, resulting from a non-disjunction event during meiosis. This means that the condition can occur in any individual, regardless of sex. The presence of an extra copy of chromosome 21 disrupts the normal balance of genetic material, leading to the characteristic physical and developmental features associated with Down's Syndrome.

**Why Each Wrong Option is Incorrect**
**Option B:** Simian crease, also known as a single palmar crease, is a common feature found in individuals with Down's Syndrome. This characteristic is not exclusive to the condition but is a common finding in affected individuals.

**Option C:** Growth retardation is a common feature of Down's Syndrome, particularly during infancy and early childhood. Affected individuals may experience delayed growth and development, which can be due to various factors, including nutritional deficiencies, hormonal imbalances, and other medical complications.

**Option D:** Epicanthus with oblique palpebral fissure is a characteristic feature of Down's Syndrome. The epicanthic fold, which is a skin fold at the inner corner of the eye, is often present in individuals with the condition.

**Clinical Pearl / High-Yield Fact**
It's essential to remember that Down's Syndrome is a chromosomal disorder that affects both males and females, and its characteristic features can vary in severity and presentation. A thorough physical examination and genetic testing are crucial for diagnosis.

**✓ Correct Answer: A. Only found in female**