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Genome Annotation and Assembly

Genome Annotation and Assembly

The genome refers to all of the genetic material in an organism. It can range from a few million base pairs in microbial cells to several billion base pairs in many eukaryotic organisms. Genome assembly refers to the process of taking the DNA sequencing data and putting it all back together in a correct order to create a close representation of the original genome. This is followed by the identification of functional elements on the newly assembled genome, a process called genome annotation.

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.

Gene Evolution - Fast or Slow?

Gene Evolution - Fast or Slow?

The genomes of eukaryotes are punctuated by long stretches of sequence which do not code for proteins or RNAs. Although some of these regions do contain crucial regulatory sequences, the vast majority of this DNA serves no known function. Typically, these regions of the genome are the ones in which the fastest change, in evolutionary terms, is observed, because there is typically little to no selection pressure acting on these regions to preserve their sequences.
In contrast, regions which code...

Evolutionary Relationships through Genome Comparisons

Evolutionary Relationships through Genome Comparisons

Genome comparison is one of the excellent ways to interpret the evolutionary relationships between organisms. The basic principle of genome comparison is that if two species share a common feature, it is likely encoded by the DNA sequence conserved between both species. The advent of genome sequencing technologies in the late 20th century enabled scientists to understand the concept of conservation of domains between species and helped them to deduce evolutionary relationships across diverse...

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Updated: Jun 27, 2026

High-throughput Identification of Gene Regulatory Sequences Using Next-generation Sequencing of Circular Chromosome Conformation Capture (4C-seq)

High-throughput Identification of Gene Regulatory Sequences Using Next-generation Sequencing of Circular Chromosome Conformation Capture (4C-seq)

Published on: October 5, 2018

Assessing the gene space in draft genomes.

Genis Parra¹, Keith Bradnam, Zemin Ning

¹UC Davis Genome Center, University of California Davis, Davis, CA, USA.

Nucleic Acids Research

|December 2, 2008

Summary

This summary is machine-generated.

Evaluating the completeness of eukaryotic gene catalogs in draft genomes is crucial. A new metric using core eukaryotic genes (CEGs) effectively assesses gene space completeness, complementing existing measures.

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High-throughput Identification of Gene Regulatory Sequences Using Next-generation Sequencing of Circular Chromosome Conformation Capture (4C-seq)

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G2-seq: A High Throughput Sequencing-based Technique for Identifying Late Replicating Regions of the Genome

G2-seq: A High Throughput Sequencing-based Technique for Identifying Late Replicating Regions of the Genome

Published on: March 22, 2018

Area of Science:

Genomics
Bioinformatics
Evolutionary Biology

Background:

Genome sequencing projects are underway for many eukaryotes, but most yield draft assemblies, not complete genomes.
A key goal of genome sequencing is to identify the complete set of genes (gene catalog).
Assessing the completeness of gene catalogs in unfinished eukaryotic genomes is challenging.

Purpose of the Study:

To develop a reliable metric for evaluating the completeness of gene catalogs in draft eukaryotic genomes.
To identify a set of highly conserved core eukaryotic genes (CEGs) suitable for this metric.
To compare the utility of the CEG-based metric with traditional assembly statistics like N50 and coverage.

Main Methods:

Identification of a set of core eukaryotic genes (CEGs) characterized by high conservation and low copy number in higher eukaryotes.
Analysis of phylogenetically diverse eukaryotic genome assemblies to map the identified CEGs.
Calculation of the proportion of mapped CEGs as a metric for gene space completeness.

Main Results:

The proportion of mapped core eukaryotic genes (CEGs) in draft genomes serves as a valuable metric for gene space completeness.
This CEG-based metric provides complementary information to standard assembly metrics such as N50 length and x-fold coverage.
The findings are applicable across a phylogenetically diverse range of eukaryotic genome assemblies.

Conclusions:

The proportion of mapped core eukaryotic genes (CEGs) offers a robust method for assessing gene catalog completeness in draft eukaryotic genomes.
This metric enhances the evaluation of genome assembly quality beyond traditional measures.
The study provides a framework for more accurate gene space characterization in ongoing and future eukaryotic genome projects.