Gene Families Are a Sub-aspect of Single Copy Sequences

Phylogenetic tree of the Mup gene family unit

A cistron family unit is a fix of several like genes, formed by duplication of a single original factor, and generally with similar biochemical functions. 1 such family are the genes for human being hemoglobin subunits; the x genes are in two clusters on different chromosomes, called the α-globin and β-globin loci. These 2 gene clusters are idea to have arisen every bit a result of a forerunner cistron being duplicated approximately 500 1000000 years agone.^[1]

Genes are categorized into families based on shared nucleotide or protein sequences. Phylogenetic techniques can be used equally a more rigorous test. The positions of exons within the coding sequence can be used to infer common ancestry. Knowing the sequence of the poly peptide encoded by a gene can allow researchers to utilize methods that find similarities amidst protein sequences that provide more than information than similarities or differences among Dna sequences.

If the genes of a gene family encode proteins, the term protein family is often used in an analogous manner to gene family.

The expansion or contraction of cistron families forth a specific lineage tin can exist due to chance, or tin be the issue of natural selection.^[two] To distinguish between these two cases is often difficult in practice. Recent work uses a combination of statistical models and algorithmic techniques to detect gene families that are under the effect of natural choice.^[3]

The HUGO Gene Nomenclature Committee (HGNC) creates nomenclature schemes using a "stem" (or "root") symbol for members of a gene family (past homology or office), with a hierarchical numbering organization to distinguish the individual members.^{[iv] [5]} For instance, for the peroxiredoxin family, PRDX is the root symbol, and the family members are PRDX1, PRDX2, PRDX3, PRDX4, PRDX5, and PRDX6.

Basic structure [edit]

I level of genome organization is the grouping of genes into several gene families.^{[6] [vii]} Gene families are groups of related genes that share a mutual ancestor. Members of gene families may be paralogs or orthologs. Factor paralogs are genes with like sequences from within the same species while gene orthologs are genes with similar sequences in different species. Factor families are highly variable in size, sequence diversity, and system. Depending on the diversity and functions of the genes inside the family, families can be classified as multigene families or superfamilies.^{[half dozen] [8]}

Multigene families typically consist of members with similar sequences and functions, though a high caste of divergence (at the sequence and/or functional level) does non lead to the removal of a gene from a gene family. Individual genes in the family may exist arranged close together on the same chromosome or dispersed throughout the genome on different chromosomes. Due to the similarity of their sequences and their overlapping functions, private genes in the family oft share regulatory command elements.^{[6] [8]} In some instances, gene members have identical (or nearly identical) sequences. Such families permit for massive amounts of gene product to be expressed in a short time as needed. Other families permit for similar just specific products to be expressed in different cell types or at different stages of an organisms development.^[half-dozen]

Superfamilies are much larger than single multigene families. Superfamilies contain up to hundreds of genes, including multiple multigene families also as single, individual gene members. The large number of members allows superfamilies to be widely dispersed with some genes amassed and some spread far autonomously. The genes are diverse in sequence and function displaying various levels of expression and divide regulation controls.^{[vi] [8]}

Some gene families also comprise pseudogenes, sequences of DNA that closely resemble established factor sequences but are non-functional.^[ix] Different types of pseudogenes exist. Non-processed pseudogenes are genes that caused mutations over time becoming non-functional. Processed pseudogenes are genes that have lost their function after being moved around the genome by retrotransposition.^{[8] [nine]} Pseudogenes that have go isolated from the gene family they originated in, are referred to as orphans.^[half-dozen]

Formation [edit]

Gene families arose from multiple duplications of an ancestral gene, followed by mutation and difference.^[six] Duplications tin can occur inside a lineage (e.one thousand., humans might accept ii copies of a gene that is found only once in chimpanzees) or they are the result of speciation. For example, a single gene in the ancestor of humans and chimpanzees at present occurs in both species and tin be thought of equally having been 'duplicated' via speciation. As a upshot of duplication past speciation, a cistron family might include 15 genes, one re-create in each of 15 different species.

Duplication [edit]

In the formation of cistron families, 4 levels of duplication be: 1) exon duplication and shuffling, ii) entire gene duplication, 3) multigene family duplication, and iv) whole genome duplication. Exon duplication and shuffling gives rising to variation and new genes. Genes are then duplicated to class multigene families which duplicate to form superfamilies spanning multiple chromosomes. Whole genome duplication doubles the number of copies of every gene and gene family.^[6] Whole genome duplication or polyploidization tin be either autopolyploidization or alloploidization. Autopolyploidization is the duplication of the same genome and allopolyploidization is the duplication of two closely related genomes or hybridized genomes from different species.^[8]

Duplication occurs primarily through uneven crossing over events in meiosis of germ cells. (1,2) When 2 chromosomes misalign, crossing over - the commutation of gene alleles - results in one chromosome expanding or increasing in gene number and the other contracting or decreasing in cistron number. The expansion of a gene cluster is the duplication of genes that leads to larger gene families.^{[6] [8]}

Relocation [edit]

Gene members of a multigene family or multigene families inside superfamilies exist on different chromosomes due to relocation of those genes afterward duplication of the bequeathed gene. Transposable elements play a role in the movement of genes. Transposable elements are recognized past inverted repeats at their 5' and 3' ends. When ii transposable elements are close enough in the aforementioned region on a chromosome, they can form a composite transposon. The poly peptide transposase recognizes the outermost inverted repeats, cutting the DNA segment. Any genes between the two transposable elements are relocated equally the composite transposon jumps to a new area of the genome.^[6]

Reverse transcription is another method of gene motility. An mRNA transcript of a gene is reversed transcribed, or copied, dorsum into DNA. This new Deoxyribonucleic acid copy of the mRNA is integrated into another office of the genome, resulting in factor family members being dispersed.^[viii]

A special blazon of multigene family is implicated in the motion of gene families and gene family members. LINE (Long INterspersed Elements) and SINE (Short INterspersed Elements) families are highly repetitive DNA sequences spread all throughout the genome. The LINEs contain a sequence that encodes a opposite transcriptase protein. This protein aids in copying the RNA transcripts of LINEs and SINEs dorsum into Dna, and integrates them into different areas of the genome. This cocky-perpetuates the growth of LINE and SINE families. Due to the highly repetitive nature of these elements, LINEs and SINEs when close together besides trigger unequal crossing over events which consequence in single-gene duplications and the formation of gene families.^{[6] [8]}

Divergence [edit]

Non-synonymous mutations resulting in the substitution of amino acids, increment in duplicate gene copies. Duplication gives rising to multiple copies of the same factor, giving a level of back-up where mutations are tolerated. With one operation copy of the gene, other copies are able to larn mutations without being extremely detrimental to the organisms. Mutations allow duplicate genes to learn new or different functions.^[8]

Concerted evolution [edit]

Some multigene families are extremely homogenous, with individual genes members sharing identical or near identical sequences. The procedure past which gene families maintain high homogeneity is Concerted evolution. Concerted evolution occurs through repeated cycles of diff crossing over events and repeated cycles of gene transfer and conversion. Unequal crossing over leads to the expansion and contraction of gene families. Gene families have an optimal size range that natural selection acts towards. Contraction deletes divergent cistron copies and keeps gene families from becoming too large. Expansion replaces lost gene copies and prevents gene families from condign as well small. Repeat cycles of factor transfer and conversion increasingly make gene family members more than similar.^[6]

In the process of cistron transfer, allelic gene conversion is biased. Mutant alleles spreading in a gene family towards homogeneity is the aforementioned process of an advantageous allele spreading in a population towards fixation. Gene conversion also aids in creating genetic variation in some cases.^[10]

Evolution [edit]

Gene families, part of a hierarchy of information storage in a genome, play a large role in the evolution and diversity of multicellular organisms. Gene families are large units of data and genetic variability.^[6] Over evolutionary time, factor families have expanded and contracted with new cistron families being formed and some cistron families being lost. In several evolutionary lineages, genes are gained and lost at relatively same rates. Adaptive expansion of gene families occurs when natural selection would favour boosted gene copies. This is the case when an environmental stressor acts on a species. Gene amplification is more than common in leaner and is a reversible process. Adaptive wrinkle of gene families commonly results from accumulation of loss of office mutations. A nonsense mutation which prematurely halts gene transcription becomes stock-still in the population, leading to the loss of genes. This process occurs when changes in the environment render a gene redundant.^[7]

New factor families originate from orphan genes (isolated pseudogenes). These isolated genes occur by dissimilar hateful. A gene duplicate accumulates plenty mutations to be sufficiently divergent to no longer exist recognized every bit part of the original cistron family, horizontal transfer of new genes into a genome, or a new cistron originate de novo from non-coding sequences. These orphan genes would then go through the processes of duplication, relocation and departure to form a family. Gene family death occurs when the loss of a factor leads to the loss of the entire factor family. The continuous loss of genes eventually leads to the extinction of the gene family. Gene loss may be the deletion of genes or the complete loss of function, condign pseudogenes.^[vii]

Functional family [edit]

In addition to classification by development (structural gene family), the HGNC besides makes "factor families" past role in their stalk nomenclature.^[eleven] As a issue, a stem tin likewise refer to genes that have the same function, often part of the aforementioned protein complex. For example, BRCA1 and BRCA2 are unrelated genes that are both named for their function in breast cancer and RPS2 and RPS3 are unrelated ribosomal proteins found in the same pocket-sized subunit.

The HGNC also maintains a "gene grouping" (formerly "factor family") classification. A gene tin be a member of multiple groups, and all groups form a hierarchy. Equally with the stem classification, both structural and functional groups be.^{[4] [v]}

See also [edit]

• Listing of gene families
• Protein family

References [edit]

1. ^ Nussbaum, Robert 50.; McInnes, Roderick R.; Willard, ikksiiskHuntington F. (2016). Thompson & Thompson Genetics in Medicine (8th ed.). Philadelphia, PA: Elsevier. p. 25. ISBN978-ane-4377-0696-iii.
2. ^ Hartl, D.L. and Clark A.G. 2007. Principles of population genetics. Affiliate 7, page 372.
3. ^ Demuth, Jeffery P.; Bie, Tijl De; Stajich, Jason E.; Cristianini, Nello; Hahn, Matthew W.; Borevitz, Justin (20 December 2006). "The Evolution of Mammalian Gene Families". PLOS 1. i (1): e85. Bibcode:2006PLoSO...1...85D. doi:10.1371/journal.pone.0000085. PMC1762380. PMID 17183716.
4. ^ ^{a b} Daugherty, LC; Seal, RL; Wright, MW; Bruford, EA (Jul 5, 2012). "Gene family matters: expanding the HGNC resource". Homo Genomics. 6 (1): 4. doi:x.1186/1479-7364-half dozen-iv. PMC3437568. PMID 23245209.
5. ^ ^{a b} HGNC. "Cistron group help". Retrieved 2020-x-thirteen .
6. ^ ^{a b c d east f g h i j k l m} Hartwell, Leland H.; et al. (2011). Genetics : from genes to genomes (quaternary ed.). New York: McGraw-Colina. ISBN978-0073525266.
7. ^ ^{a b c} Demuth, JP; Hahn, MW (January 2009). "The life and death of gene families". BioEssays. 31 (1): 29–39. doi:ten.1002/bies.080085. PMID 19153999. S2CID 9528185.
8. ^ ^{a b c d e f g h i} Ohta, Tomoka (2008). "Gene families: multigene families and superfamilies". eLS. doi:x.1038/npg.els.0005126. ISBN978-0470015902.
9. ^ ^{a b} Nussbaum, Robert L; et al. (2015). Genetics in Medicine (viii ed.). Philadelphia: Elsevier. ISBN9781437706963.
10. ^ Ohta, T (30 September 2010). "Cistron conversion and evolution of cistron families: an overview". Genes. one (iii): 349–56. doi:ten.3390/genes1030349. PMC3966226. PMID 24710091.
11. ^ "What is a stem symbol?". HGNC FAQ.

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Source: https://en.wikipedia.org/wiki/Gene_family

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