Nuclear gene

A nuclear gene is a gene whose DNA sequence is located within the cell nucleus of a eukaryotic organism. These genes are distinguished from extranuclear genes, such as those found in the genomes of mitochondria and chloroplasts, which reside outside the nucleus in their own organellar DNA. Nuclear genes encode the majority of proteins and functional RNAs required for cellular processes, including development, metabolism, and regulation.

Unlike the small, circular genomes of mitochondria and chloroplasts, nuclear genes are organized into linear chromosomes and are typically inherited in a Mendelian fashion, following the laws of segregation and independent assortment. In contrast, extranuclear genes often exhibit non-Mendelian inheritance, such as maternal inheritance in mitochondrial DNA.

While the vast majority of eukaryotic genes are nuclear, exceptions exist in certain protists and algae, where some genes have migrated from organelles to the nucleus over evolutionary time through endosymbiotic gene transfer. The study of nuclear genes is fundamental to genetics, molecular biology, and biotechnology, as they play a central role in gene expression, heredity, and genetic engineering.