Genome
[7] The term genome was created in 1920 by Hans Winkler,[8] professor of botany at the University of Hamburg, Germany.
A few related -ome words already existed, such as biome and rhizome, forming a vocabulary into which genome fits systematically.
In 1976, Walter Fiers at the University of Ghent (Belgium) was the first to establish the complete nucleotide sequence of a viral RNA-genome (Bacteriophage MS2).
The next year, Fred Sanger completed the first DNA-genome sequence: Phage X174, of 5386 base pairs.
A few months later, the first eukaryotic genome was completed, with sequences of the 16 chromosomes of budding yeast Saccharomyces cerevisiae published as the result of a European-led effort begun in the mid-1980s.
[18] Among the thousands of completed genome sequencing projects include those for rice, a mouse, the plant Arabidopsis thaliana, the puffer fish, and the bacteria E. coli.
[25] However, some symbiotic bacteria (e.g. Serratia symbiotica) have reduced genomes and a high fraction of pseudogenes: only ~40% of their DNA encodes proteins.
The amount is even more than what is necessary for DNA protein-coding and noncoding genes because eukaryotic genomes show as much as 64,000-fold variation in their sizes.
A typical human cell has two copies of each of 22 autosomes, one inherited from each parent, plus two sex chromosomes, making it diploid.
Gametes, such as ova, sperm, spores, and pollen, are haploid, meaning they carry only one copy of each chromosome.
Sequence polymorphisms are typically discovered by comparing resequenced isolates to a reference, whereas analyses of coverage depth and mapping topology can provide details regarding structural variations such as chromosomal translocations and segmental duplications.
For example, telomeres are composed of the tandem repeat TTAGGG in mammals, and they play an important role in protecting the ends of the chromosome.
[34] For example, the human gene huntingtin (Htt) typically contains 6–29 tandem repeats of the nucleotides CAG (encoding a polyglutamine tract).
The mechanism by which proteins with expanded polygulatamine tracts cause death of neurons is not fully understood.
One possibility is that the proteins fail to fold properly and avoid degradation, instead accumulating in aggregates that also sequester important transcription factors, thereby altering gene expression.
[35] Transposable elements (TEs) are sequences of DNA with a defined structure that are able to change their location in the genome.
[43] Short interspersed elements (SINEs) are usually less than 500 base pairs and are non-autonomous, so they rely on the proteins encoded by LINEs for transposition.
When expressed, the transposase recognizes the terminal inverted repeats that flank the transposon and catalyzes its excision and reinsertion in a new site.
[45] There is no clear and consistent correlation between morphological complexity and genome size in either prokaryotes or lower eukaryotes.
[30] Eukaryote genomes often contain many thousands of copies of these elements, most of which have acquired mutations that make them defective.
In some cases, such mutations lead to cancer because they cause cells to divide more quickly and invade surrounding tissues.
During this process, recombination results in a reshuffling of the genetic material from homologous chromosomes so each gamete has a unique genome.
Genome-wide reprogramming in mouse primordial germ cells involves epigenetic imprint erasure leading to totipotency.
Researchers compare traits such as karyotype (chromosome number), genome size, gene order, codon usage bias, and GC-content to determine what mechanisms could have produced the great variety of genomes that exist today (for recent overviews, see Brown 2002; Saccone and Pesole 2003; Benfey and Protopapas 2004; Gibson and Muse 2004; Reese 2004; Gregory 2005).
Horizontal gene transfer is invoked to explain how there is often an extreme similarity between small portions of the genomes of two organisms that are otherwise very distantly related.
Also, eukaryotic cells seem to have experienced a transfer of some genetic material from their chloroplast and mitochondrial genomes to their nuclear chromosomes.
A chaos theorist is asked to give his expert opinion on the safety of engineering an ecosystem with the dinosaurs, and he repeatedly warns that the outcomes of the project will be unpredictable and ultimately uncontrollable.
The 1997 film Gattaca is set in a futurist society where genomes of children are engineered to contain the most ideal combination of their parents' traits, and metrics such as risk of heart disease and predicted life expectancy are documented for each person based on their genome.
People conceived outside of the eugenics program, known as "In-Valids" suffer discrimination and are relegated to menial occupations.
The film warns against a future where genomic information fuels prejudice and extreme class differences between those who can and cannot afford genetically engineered children.
