Genetics terminology — What does the term ‘‘homologous chromosomes’’ mean in the context of a diploid organism?

Introduction / Context:
Clear terminology is essential in genetics. ‘‘Homologous chromosomes’’ are central to understanding inheritance, meiosis, linkage, and mapping. This question distinguishes homologs from sister chromatids and clarifies ploidy implications.

Given Data / Assumptions:

• Diploid cells contain pairs of homologous chromosomes.
• Each homolog originates from a different parent.
• Homologs carry the same gene loci in the same linear order, though alleles can differ.

Concept / Approach:
Sister chromatids are identical DNA copies generated during replication and joined at the centromere; homologous chromosomes are similar but not identical, representing maternal and paternal versions. Homology refers to shared loci, not necessarily identical sequence or alleles.

Step-by-Step Solution:

Verification / Alternative check:
Cytogenetics shows bivalents of homologs pairing in meiosis I, confirming the functional definition used in classical genetics.

Why Other Options Are Wrong:

• a/b: Describe sister chromatids, not homologs.
• c: Homologs exist as pairs in diploids, not necessarily haploid.
• e: Size alone is insufficient; locus order matters.

Common Pitfalls:
Equating homology with 100% sequence identity; confusing meiosis I homolog separation with mitotic chromatid separation.

Final Answer:
A pair of chromosomes of the same kind, one maternal and one paternal, carrying the same gene loci (homologs).