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Genome Size and the Evolution of New Genes

Genome Size and the Evolution of New Genes

While every living organism has a genome of some kind (be it RNA, or DNA), there is considerable variation in the sizes of these blueprints. One major factor that impacts genome size is whether the organism is prokaryotic or eukaryotic. In prokaryotes, the genome contains little to no non-coding sequence, such that genes are tightly clustered in groups or operons sequentially along the chromosome. Conversely, the genes in eukaryotes are punctuated by long stretches of non-coding sequence.

Genome Size and the Evolution of New Genes

Genome Size and the Evolution of New Genes

While every living organism has a genome of some kind (be it RNA, or DNA), there is considerable variation in the sizes of these blueprints. One major factor that impacts genome size is whether the organism is prokaryotic or eukaryotic. In prokaryotes, the genome contains little to no non-coding sequence, such that genes are tightly clustered in groups or operons sequentially along the chromosome. Conversely, the genes in eukaryotes are punctuated by long stretches of non-coding sequence.

Gene Duplication and Divergence

Gene Duplication and Divergence

The seminal work of Ohno in 1970 popularized the idea of gene duplication and divergence. DNA sequence comparison studies reveal that a large portion of the genes in bacteria, archaebacteria, and eukaryotes was generated by gene duplication and divergence, indicating its critical role in evolution.
The duplicated copies of the gene are called Paralogs. Paralogs with similar sequences and functions form a gene family. Across several species, a large number of gene families are characterized.

DNA as a Genetic Template

DNA as a Genetic Template

Two structural features of the DNA molecule provide a basis for the mechanisms of heredity: the four nucleotide bases and its double-stranded nature. The Watson-Crick model of double-helical DNA structure, proposed in 1952, drew heavily upon the X-ray crystallography work of researchers Rosalind Franklin and Maurice Wilkins. Watson, Crick, and Wilkins jointly received the Nobel Prize in Physiology or Medicine for their work in 1962. Franklin was, controversially, excluded from the prize for...

DNA as a Genetic Template

DNA as a Genetic Template

Two structural features of the DNA molecule provide a basis for the mechanisms of heredity: the four nucleotide bases and its double-stranded nature. The Watson-Crick model of double-helical DNA structure, proposed in 1952, drew heavily upon the X-ray crystallography work of researchers Rosalind Franklin and Maurice Wilkins. Watson, Crick, and Wilkins jointly received the Nobel Prize in Physiology or Medicine for their work in 1962. Franklin was, controversially, excluded from the prize for...

Genomic DNA in Eukaryotes

Genomic DNA in Eukaryotes

Eukaryotes have large genomes compared to prokaryotes. To fit their genomes into a cell, eukaryotic DNA is packaged extraordinarily tightly inside the nucleus. To achieve this, DNA is tightly wound around proteins called histones, which are packaged into nucleosomes that are joined by linker DNA and coil into chromatin fibers. Additional fibrous proteins further compact the chromatin, which is recognizable as chromosomes during certain phases of cell division.

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Related Experiment Video

Updated: Jun 4, 2026

Mapping Mammalian 3D Genome Interactions with Micro-C-XL

Mapping Mammalian 3D Genome Interactions with Micro-C-XL

Published on: November 3, 2023

Barking up the wrong genome--we are not alone.

A Li-Wan-Po¹, P Farndon

¹National Genetics Education and Development Centre, c/o Birmingham's Women's Hospital, Edgbaston, Birmingham, UK. a.liwanpo@talk21.com

Journal of Clinical Pharmacy and Therapeutics

|March 4, 2011

Summary

The human microbiome significantly impacts drug response variability. Targeting bacterial enzymes in the gut can reduce side effects from cancer drugs like irinotecan, highlighting a new frontier in personalized medicine.

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Area of Science:

Pharmacology
Microbiology
Genetics

Background:

Pharmacogenetic studies traditionally focus on host germline mutations and pathogen/tumor cell mutations.
The role of the human microbiome in drug response variability is increasingly recognized.
Understanding microbiome contributions is crucial for personalized medicine.

Purpose of the Study:

To highlight the role of the microbiome in drug response variability.
To discuss the impact of gut bacteria on the efficacy and toxicity of anticancer drugs.
To emphasize the need to consider the microbiome in personalized medicine strategies.

Main Methods:

Review of existing literature on pharmacogenetics and the microbiome.
Analysis of a case study involving irinotecan and its metabolite SN-38.
Discussion of experimental approaches using microbial enzyme inhibitors in preclinical models.

Main Results:

The anticancer drug irinotecan's metabolite (SN-38) is reactivated by bacterial β-glucuronidases in the gut.
This reactivation contributes to irinotecan-induced gastrointestinal toxicity.
Inhibiting these microbial enzymes reduced toxicity in mouse models.

Conclusions:

The microbiome plays a critical role in drug metabolism and toxicity.
Targeting microbial enzymes offers a novel strategy for mitigating drug-induced side effects.
Personalized medicine must integrate host genetics with microbiome analysis for optimal patient outcomes.