Autosome
An autosome is any chromosome that is not a sex chromosome.[1] The members of an autosome pair in a diploid cell typically have the same morphology (homomorphic), unlike those in allosomal (sex chromosome) pairs, which may have different structures. The DNA in autosomes is collectively known as atDNA or auDNA.[2]
Nomenclature
[edit]The number of autosomal chromosomes an organism has can vary across species and cell types. They are typically identified by sequential numbers beginning with 1 (as opposed to the sex chromosomes which are indicated by letters).
In diploid organisms, a somatic cell will contain two copies of each autosomal chromosome, one from each parent while germline cells (eggs or sperm) will typically contain a single copy of each autosome. The homologous chromosome pairs are identified with the same number (e.g. a somatic cell will have two copies of chromosome 1, two copies of chromosome 2...).
Humans
[edit]The human genome contains 44 autosomal chromosomes, or as a diploid organism, 22 pairs of homologous autosomes that are numbered 1-22. These autosome pairs were labeled with numbers (1–22 in humans) roughly in order of their sizes in base pairs.[3]
All human autosomes have been identified and mapped by extracting the chromosomes from a cell arrested in metaphase or prometaphase and then staining them with a type of dye (most commonly, Giemsa).[4] These chromosomes are typically viewed as karyograms for easy comparison. Clinical geneticists can compare the karyogram of an individual to a reference karyogram to discover the cytogenetic basis of certain phenotypes. For example, the karyogram of someone with Patau Syndrome would show that they possess three copies of chromosome 13. Karyograms and staining techniques can only detect large-scale disruptions to chromosomes—chromosomal aberrations smaller than a few million base pairs generally cannot be seen on a karyogram.[5]
| Karyotype of human chromosomes | |
|---|---|
| Female (XX) | Male (XY) |
 |
 |
| There are two copies of each autosome (chromosomes 1–22) in both females and males. The sex chromosomes are different: There are two copies of the X-chromosome in females, but males have a single X-chromosome and a Y-chromosome. | |
Autosomes still contain sexual determination genes even though they are not sex chromosomes. For example, mutations of the SOX9 gene on chromosome 17 can cause humans with a typical Y chromosome to develop as females. The transcription factor TDF (encoded by the SRY gene on the Y sex chromosome), a protein vital for male sex determination during development, functions by activating SOX9 and that the mutation on SOX9 causes the gene to be activated without the TDR transcription factor.[6]
Yeast
[edit]The yeast (S. cerevisiae) genome has 16 chromosomes in its haploid state (32 in its diploid state). However, unlike other organisms, they are officially numbered with roman numerals (I to XVI). [7] As an organism being studied before the development of technologies for directly observing and counting chromosomes, their chromosome numbering was based on the order of their discovery in the 1950's rather than by their lengths. [8] When the entire genome was published in 1996 as the first eukaryote to have its entire genome sequenced, the roman numeral-based naming convention was continued by naming each assembled chromsome in the reference "chrI", "chrII", ... "chrVXI." [9]
Autosomal genetic disorders
[edit]
Autosomal genetic disorders can arise due to a number of causes, some of the most common being nondisjunction in parental germ cells or Mendelian inheritance of deleterious alleles from parents. Autosomal genetic disorders which exhibit Mendelian inheritance can be inherited either in an autosomal dominant or recessive fashion.[10] These disorders manifest in and are passed on by either sex with equal frequency.[10][11] Autosomal dominant disorders are often present in both parent and child, as the child needs to inherit only one copy of the deleterious allele to manifest the disease. Autosomal recessive diseases, however, require two copies of the deleterious allele for the disease to manifest. Because it is possible to possess one copy of a deleterious allele without presenting a disease phenotype, two phenotypically normal parents can have a child with the disease if both parents are carriers (also known as heterozygotes) for the condition.
Autosomal aneuploidy can also result in disease conditions. Aneuploidy of autosomes is not well tolerated and usually results in miscarriage of the developing fetus. Fetuses with aneuploidy of gene-rich chromosomes—such as chromosome 1—never survive to term,[12] and fetuses with aneuploidy of gene-poor chromosomes—such as chromosome 21— are still miscarried over 23% of the time.[13] Possessing a single copy of an autosome (known as a monosomy) is nearly always incompatible with life, though very rarely some monosomies can survive past birth. Having three copies of an autosome (known as a trisomy) is far more compatible with life, however. A common example is Down syndrome (trisomy 21), which is caused by possessing three copies of chromosome 21 instead of the usual two.[12] Other examples of human autosomal trisomy with documented cases of surviving to term include Edwards syndrome (trisomy 18), Patau syndrome (trisomy 13), Warkany syndrome 2 (trisomy 8) Trisomy 9, and Trisomy_22 which are associated with number of disorders.
Partial aneuploidy can also occur as a result of unbalanced translocations during meiosis.[14] Deletions of part of a chromosome cause partial monosomies, while duplications can cause partial trisomies. If the duplication or deletion is large enough, it can be discovered by analyzing a karyogram of the individual. Autosomal translocations can be responsible for a number of diseases, ranging from cancer to schizophrenia.[15][16] Unlike single gene disorders, diseases caused by aneuploidy are the result of improper gene dosage, not nonfunctional gene product.[17]
See also
[edit]- Aneuploidy (abnormal number of chromosomes)
- Autosomal dominant
- Autosomal recessive
- Homologous chromosome
- Pseudoautosomal region
- XY sex-determination system
- Genetic disorder
References
[edit]- ^ Griffiths, Anthony J. F. (1999). An Introduction to genetic analysis. New York: W.H. Freeman. ISBN 978-0-7167-3771-1. Archived from the original on January 27, 2012.
- ^ "Autosomal DNA - ISOGG Wiki". www.isogg.org. Archived from the original on 21 August 2017. Retrieved 28 April 2018.
- ^ "Autosome Definition(s)". Genetics Home Reference. Archived from the original on 2 January 2016. Retrieved 28 April 2018.
- ^ "Chromosome mapping Facts, information, pictures". encyclopedia.com. Encyclopedia.com articles about Chromosome mapping. Archived from the original on 10 December 2015. Retrieved 4 December 2015.
- ^ Nussbaum RL, McInnes RR, Willard HF, Hamosh A, Thompson MW (2007). Thompson & Thompson Genetics in Medicine (7th ed.). Philadelphia, PA: Saunders/Elsevier. p. 69. ISBN 9781416030805.
- ^ Foster JW, Dominguez-Steglich MA, Guioli S, Kwok C, Weller PA, Stevanović M, Weissenbach J, Mansour S, Young ID, Goodfellow PN (December 1994). "Complicate dysplasia and autosomal sex reversal caused by mutations in an SRY-related gene". Nature. 372 (6506): 525–30. Bibcode:1994Natur.372..525F. doi:10.1038/372525a0. PMID 7990924. S2CID 1472426.
- ^ Engel, Stacia; Fred S Dietrich; Dianna G Fisk; Gail Binkley; Rama Balakrishnan; Maria C Costanzo; Selina S Dwight; Benjamin C Hitz; Kalpana Karra; Robert S Nash; Shuai Weng; Edith D Wong; Paul Lloyd; Marek S Skrzypek; Stuart R Miyasato; Matt Simison; J Michael Cherry (2013). "The Reference Genome Sequence of Saccharomyces cerevisiae: Then and Now". G3 (Bethesda). 4 (3): 389–398. doi:10.1534/g3.113.008995. PMC 3962479. PMID 24374639.
- ^ Lindegren, C. C.; Lindegren G.; Shult E. E.; Desborough S. (1959). "Chromosome maps of Saccharomyces". Nature. 183: 800–802. doi:10.1038/183800a0. PMID 13644197.
- ^ Goffeau, A; B. G. Barrell; H. Bussey; R. W. Davis; B. Dujon; H. Feldmann; F. Galibert; J. D. Hoheisel; C. Jacq; M. Johnston; E. J. Louis; H. W. Mewes; Y. Murakami; P. Philippsen; H. Tettelin; S. G. Oliver (1996). "Life with 6000 genes". Nature. 274 (5287): 546, 563–7. doi:10.1126/science.274.5287.546. PMID 8849441.
- ^ a b "human genetic disease". Encyclopædia Britannica. Archived from the original on 2015-10-13. Retrieved 2015-10-16.
- ^ Chial, Heidi (2008). "Mendelian Genetics: Patterns of Inheritance and Single-Gene Disorders". Nature Education. 1 (1): 63.
- ^ a b Wang, Jin-Chen C. (2005-01-01). "Autosomal Aneuploidy". In Gersen, Steven L.; MEd, Martha B. Keagle (eds.). The Principles of Clinical Cytogenetics. Humana Press. pp. 133–164. doi:10.1385/1-59259-833-1:133. ISBN 978-1-58829-300-8.
- ^ Savva, George M.; Morris, Joan K.; Mutton, David E.; Alberman, Eva (June 2006). "Maternal age-specific fetal loss rates in Down syndrome pregnancies". Prenatal Diagnosis. 26 (6): 499–504. doi:10.1002/pd.1443. PMID 16634111. S2CID 34154717.
- ^ "Translocation - Glossary Entry". Genetics Home Reference. 2015-11-02. Archived from the original on 2015-12-09. Retrieved 2015-11-08.
- ^ Strefford, Jonathan C.; An, Qian; Harrison, Christine J. (31 October 2014). "Modeling the molecular consequences of unbalanced translocations in cancer: Lessons from acute lymphoblastic leukemia". Cell Cycle. 8 (14): 2175–2184. doi:10.4161/cc.8.14.9103. PMID 19556891.
- ^ Klar, Amar J S (2002). "The chromosome 1;11 translocation provides the best evidence supporting genetic etiology for schizophrenia and bipolar affective disorders". Genetics. 160 (4): 1745–1747. doi:10.1093/genetics/160.4.1745. PMC 1462039. PMID 11973326.
- ^ Disteche, Christine M. (15 December 2012). "Dosage Compensation of the Sex Chromosomes". Annual Review of Genetics. 46 (1): 537–560. doi:10.1146/annurev-genet-110711-155454. PMC 3767307. PMID 22974302.