**Core Concept**
The microdeletion of the Y-chromosome, specifically the azoospermia factor (AZF) region, is a common genetic cause of male infertility. This deletion can lead to severe oligozoospermia or azoospermia, even with a normal karyotype.

**Why the Correct Answer is Right**
Patients with a normal karyotype but low sperm concentration may be at risk of having a microdeletion of the Y-chromosome. The presence of a normal karyotype does not rule out the possibility of microdeletions, which can only be detected by specific genetic testing. Sperm concentration of 2 million/ml is considered low and may warrant further investigation, including testing for microdeletions of the Y-chromosome.

**Why Each Wrong Option is Incorrect**
**Option B:** Semen volume of 2 ml is not directly related to the presence of microdeletions of the Y-chromosome. A low semen volume can be caused by various factors, including hormonal imbalances or anatomical abnormalities.

**Option C:** Presence of fructose in semen is actually a marker of normal seminal vesicle function and is not directly related to the presence of microdeletions of the Y-chromosome.

**Option D:** Normal morphology sperms >4% is a desirable parameter but does not rule out the presence of microdeletions of the Y-chromosome. Some patients with normal morphology may still have low sperm concentration due to other underlying causes.

**Clinical Pearl / High-Yield Fact**
In patients with normal karyotype but low sperm concentration, testing for microdeletions of the Y-chromosome is essential to identify potential genetic causes of male infertility. This testing can help guide fertility treatment options and predict the likelihood of success with assisted reproductive technologies.

**✓ Correct Answer: A. Sperm concentration of 2 million/ml**