**Core Concept**
Polygenic inheritance refers to the phenomenon where multiple genes contribute to the expression of a complex trait or disease, resulting in a multifactorial etiology. This is in contrast to monogenic inheritance, where a single gene is responsible for the disease.

**Why the Correct Answer is Right**
Polygenic inheritance is seen in various conditions, including hypertension. Hypertension is a complex disorder influenced by multiple genetic and environmental factors. Multiple genes regulate blood pressure, and mutations in these genes can contribute to the development of hypertension. The renin-angiotensin-aldosterone system (RAAS) is a key pathway involved in blood pressure regulation, and alterations in this system can lead to hypertension.

**Why Each Wrong Option is Incorrect**
**Option A:** Hypertension can also have a significant monogenic component, particularly in cases of familial hyperaldosteronism or primary aldosteronism.

**Option B:** Hemochromatosis (HOCM) is an autosomal dominant disorder caused by mutations in the MYBPC3 or MYH7 genes, making it a monogenic condition.

**Option C:** Manic depressive psychosis, also known as bipolar disorder, has a complex etiology involving both genetic and environmental factors. However, it is not typically considered a polygenic disorder in the same way as hypertension.

**Option D:** Familial hyperlipidemia can be caused by mutations in multiple genes, including those involved in lipid metabolism, such as the LDLR gene. However, some forms of familial hyperlipidemia, such as familial hypercholesterolemia, can be caused by mutations in a single gene.

**Clinical Pearl / High-Yield Fact**
Polygenic inheritance is a key concept in understanding the etiology of complex diseases, and it highlights the importance of considering multiple genetic and environmental factors in the diagnosis and management of these conditions.

**Correct Answer: D. Familial hyper lipidemia**