**Question:** Group of alleles that are closely linked together at a genomic locus & inherited together as a cluster is/are:

A. Dominant
B. Recessive
C. Mendelian
D. Polygenic

**Core Concept:** In genetics, an allele is a variant form of a gene that is located at a specific position on a chromosome (genomic locus). Alleles that are found together at the same location are called linked alleles, and they tend to be inherited as a unit, as if they were a single gene. This unit of linked alleles is called a gene complex or a gene cluster. When multiple genes are inherited together due to their proximity on a chromosome, it is referred to as linkage.

**Why the Correct Answer is Right:** The correct answer is D) Polygenic, because it refers to a group of alleles that are linked together and inherited as a cluster. Polygenic inheritance refers to the influence of multiple genes on a trait, where the expression of the trait depends on the combined effects of multiple genes. Unlike monogenic inheritance, where a single gene determines the trait, polygenic inheritance involves the combined action of multiple genes.

**Why Each Wrong Option is Incorrect:**

A) Dominant and Recessive alleles are types of alleles, not gene complexes or clusters. Dominant alleles express their effects regardless of the presence of another allele, while recessive alleles require two copies to express their effects. These options are incorrect because they refer to individual alleles rather than a group of linked alleles.

B) Mendelian inheritance refers to the transmission of traits based on the principles formulated by Gregor Mendel, particularly his laws of segregation and independent assortment. While Mendelian inheritance is important for understanding how genes behave, it does not specifically address linked alleles or clusters of genes. This option is incorrect as it pertains to the inheritance of single genes rather than gene clusters.

**Clinical Pearl:**

Understanding polygenic inheritance is crucial for understanding complex traits, such as height, blood type, and eye color. For example, height is determined by multiple genes, each with a small effect on the final phenotype. Inherited blood types (A, B, AB, or O) result from different combinations of the Rh factor (Rh+) and ABO antigens. Eye color is influenced by multiple genes, leading to the variation in eye color observed among individuals.

**Correct Answer Explanation:**

**Correct Answer: Polygenic (D)**

Polygenic inheritance describes the influence of multiple genes on a trait or condition, which can lead to a greater range of outcomes compared to monogenic inheritance. In this case, the correct answer is polygenic inheritance because it reflects the concept of linked alleles and gene clusters being inherited together.