Genes, which code for a pair of contrasting traits are known as:

The correct answer is Option (4) → Alleles

Genes are the units of inheritance. Alleles are genes that code for a pair of contrasting traits, such as tall and dwarf. For example, T (tall) and t (dwarf) are alleles of the gene for plant height.

(1) Chromatin — Incorrect. Chromatin is the thread-like material of the nucleus, made of DNA packed with proteins.

(2) Chromomeres — Incorrect. Chromomeres are bead-like thickened regions seen along a chromosome. They are not forms of a gene.

(3) Nucleosomes — Incorrect. A nucleosome is a unit of DNA packaging: DNA wrapped around a core of eight histone molecules.

(4) Alleles — Correct. Genes for a pair of contrasting traits are alleles.

Note: A similar question was also asked in CUET (UG) 2023 on 05-06-2023 (Slot 1).

NCERT Extract:
Inheritance of One Gene – “… Genes, therefore, are the units of inheritance. They contain the information that is required to express a particular trait in an organism. Genes which code for a pair of contrasting traits are known as alleles, i.e., they are slightly different forms of the same gene.”