Barr body is absent in female having
**Core Concept**
In humans, sex chromosomes determine the sex of an individual. Females have two X chromosomes (46, XX), while males have one X and one Y chromosome (46, XY). The Barr body is a heterochromatic structure formed from the inactivated X chromosome in females. It's a visible representation of X chromosome inactivation, a process that occurs to ensure dosage compensation between males and females.
**Why the Correct Answer is Right**
In individuals with a 45, X0 genome, also known as Turner syndrome, only one sex chromosome is present. Since there's only one X chromosome, there's no need for X chromosome inactivation, and consequently, no Barr body is formed. The absence of a Barr body in a female with a 45, X0 genome is a diagnostic feature of Turner syndrome.
**Why Each Wrong Option is Incorrect**
**Option A:** Individuals with a 46, XX genome, like most females, have two X chromosomes and therefore two Barr bodies. **Option C:** Females with a 47, XXX genome, also known as triplo-X syndrome, have three X chromosomes. While X chromosome inactivation is more complex in these individuals, it doesn't result in the complete absence of a Barr body. **Option D:** This option is incorrect because not all of the above scenarios result in the absence of a Barr body.
**Clinical Pearl / High-Yield Fact**
Turner syndrome (45, X0) is a genetic disorder that affects about 1 in 2,500 live-born females. It's characterized by short stature, ovarian dysgenesis, and various other physical and developmental abnormalities.
✓ Correct Answer: B. 45 X0 genome