In humans, two closely linked genetic loci, each made up of two alleles, compose the histocompatibility locus (HL-A). Paired first and second locus antigens are called haplotypes. The HL-A haplotypes (separated by a semicolon) of a child’s parents are given below.Father 3, 25; 7, 12Mother 1, 3; 8, 9Assuming that no cross-over events have occurred, the child’s histotype could be which of the following?

**Core Concept**
The histocompatibility locus (HL-A) is a genetic region on chromosome 6 in humans that encodes for the major histocompatibility complex (MHC) proteins. These proteins play a crucial role in the immune system by presenting peptide fragments to T-cells, thereby facilitating the recognition and response to pathogens. The HL-A complex is composed of two closely linked genetic loci, each with two alleles, resulting in a diverse range of haplotypes.

**Why the Correct Answer is Right**
The child's histotype is determined by inheriting one haplotype from each parent. Since no cross-over events have occurred, the child's haplotypes will be a combination of the parental haplotypes. The correct answer can be determined by combining the haplotypes from each parent. In this case, the child's possible histotypes are:
- **Option C:** 1, 3; 7, 12
This is the correct answer because it represents the combination of the mother's first haplotype (1, 3) and the father's second haplotype (7, 12).

**Why Each Wrong Option is Incorrect**
* **Option A:** 3, 25; 8, 9
This option is incorrect because it does not represent a combination of the parental haplotypes. The father's first haplotype is 3, 25, and the mother's second haplotype is 8, 9.
* **Option B:** 1, 3; 8, 12
This option is incorrect because the father's second haplotype is 7, 12, not 8, 12.

**Clinical Pearl / High-Yield Fact**
Understanding the concept of HL-A haplotypes is crucial in the field of transplantation medicine, where matching donor and recipient histotypes is essential for successful organ transplantation.

**Correct Answer:** C. 1, 3; 7, 12

✓ Correct Answer: B. 7, 12; 1, 3