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An autosome is a chromosome that is not an allosome (a sex chromosome).[1] Autosomes appear in pairs whose members have the same form but differ from other pairs in a diploid cell, whereas members of an allosome pair may differ from one another and thereby determine sex. The DNA in autosomes is collectively known as atDNA or auDNA.[2]
For example, humans have a Diploid genome that usually contains 22 pairs of autosomes and one allosome pair (46 chromosomes total). The autosome pairs are labeled with numbers (1-22 in humans) roughly in order of their sizes in base pairs, while allosomes are labeled with their letters.[3] By contrast, the allosome pair consists of two X chromosomes in females or one X and one Y_chromosome in males. (Unusual combinations of XYY, XXY, XXX, XXXX, XXXXX or XXYY, among other allosome combinations, are known to occur and usually cause developmental abnormalities.)
| 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. | ||
Classification of autosomes by position of centromere
[edit]Shape of autosomes are different with multiple types of centromere positions that leads to different ratio of arm lengths from the centromere to each ends of chromosomes; relative length difference of p arms(shorter arms) and q arms(longer arms) decreases in the order of telocentric (absent of one arm), acrocentric, submetacentric, and metacentric (equal length of two arms). However, in human, telocentric does not exist. Some of autosomes are structurally different from the others. For example, chromosome 13, 14, 15, 21, and 22 are acrocentric which their p arms are not directly connected to the extends of centromere but with narrow stalks (also called secondary constrictions) to satellites.[4][5]
Gene distribution and consequences of abnormality
[edit]As genes are one of main influential factors on phenotype, the number of genes on each autosome can be a brief indicator of detrimental consequences when it is altered. For example, trisomies of most autosomes can cause miscarriage but trisomies of chromosome 13, 18, and 21 sometimes results in liveborns. This is due to the fact that chromosomes 13, 18, and 21 have lowest number of genes, meaning that additional copies will have less impact than if a larger chromosome with more genes had an extra copy present. The most well known trisomy is that of chromosome 21; this condition is known as Down syndrome, and it is the most common trisomy that results liveborns.[6]
Huge portions of chromosomes are mainly used for a vital gene to avoid the consequences of detrimental mutations. For instance, highly conserved genes such as ribosomal RNA genes are mainly in narrow stalks of p arm in acrocentric choromosomes 13, 14, and 15; which provides resistance to any kinds of detrimental modifications by having lots of duplications that will compensate modified genes..[4]
In fact, there are less chances of abnormality in the quantity of chromosomes in autosomes than sex chromosomes in new born babies.[7]
Relationship with the sex-determining region of the Y
[edit]In human, sex-determining gene on the Y chromosome (SRY) in sex chromosome is responsible for male genital formation. However, not only sex chromosomes are involved in sex determination but also autosomal genes such as SOX9, NR5A1, WNT4, and CYP21A2 are also involved in major roles in sex determination.[8]
Located in the longer arm (q arm) of chromosome 17 (17q24). SOX9 is normally involved in developing genital ridge (the precursor of gonadal cells), and testis formation. Formation of testis is performed by increasing expression of SOX9 by expression of SRY gene from Y chromosome is the developmental key. In normal female with duplication of SOX9 gene, male genital will be developed due to increased amount of gene expression. In the other hand, loss of function mutation on one copy of SOX9 with functioning SOX9 gene in the sister chromatid of chromosome 17 (partial monosomy) in male will lead to failure of testis formation (camptomelic dysplasia). [9]
Located in the longer arm (q arm) of chromosome 9 (9q33). NR5A1 is normally involved in regulation of producing messenger RNA from DNA strands (transcriptional regulation) of sex determining factors in sex chromosome such as SRY and DAX1. Mutation of NR5A1 leads to the symptom which the person is hard to distinguish between genders(ambiguous genitalia), partial abnormal formation of gonad, and absent or lacking of mullerian structures (which later becomes female sex organs).
Located in the shorter arm (p arm) of chromosome 1 (1p35). Duplication of WNT4 causes symptoms which the person is hard to distinguish between genders (ambiguous genitalia) and missing testicles (cryptorchidism).
Located in the shorter arm (p arm) of chromosome 6 (6p21.3). Mutation of CYP21A2 causes symptoms which the person is hard to distinguish between genders (ambiguous genitalia), male being phenotypically female (virilization), and abnormally small male genitals (micropenis).
Bibliography
[edit]- ^ Griffiths, Anthony J. F. (1999). An Introduction to genetic analysis. New York: W.H. Freeman. ISBN 0-7167-3771-X.
- ^ http://www.isogg.org/wiki/Autosomal_DNA
- ^ http://ghr.nlm.nih.gov/glossary=autosome
- ^ a b Nussbaum, Robert L; McInnes, Roderick R; Willard, Huntington F (2015). Thompson & Thompson Genetics in Medicine. Canada: ELSEVIER. p. 58-59. ISBN 978-1-4377-0696-3.
- ^ Hartwell, Leland H.; Hood, Leroy; Goldberg, Michael L.; Reynolds, Ann E.; Silver, Lee M.; Karagiannis, Jim; Papaconstantinou, Maria (2014). Genetics: From Genes to Genomes (Canadian ed.). Canada: McGraw-Hill Education LLC. p. 74-75. ISBN 978-0-07-094669-9.
{{cite book}}:|access-date=requires|url=(help) - ^ Nussbaum, Robert L; McInnes, Roderick R; Willard, Huntington F (2015). Thompson & Thompson Genetics in Medicine. Canada: ELSEVIER. p. 65-66. ISBN 978-1-4377-0696-3.
- ^ Benn, Peter A. (2009-01-01). DCHessor, Aubrey Milunsky MB BCh, DSc, FRCP, FACMG; Director, Jeff M. Milunsky MD, FACMGessor (eds.). Prenatal Diagnosis of Chromosomal Abnormalities through Amniocentesis. Wiley-Blackwell. pp. 194–272. doi:10.1002/9781444314342.ch6/summary. ISBN 9781444314342.
{{cite book}}: CS1 maint: multiple names: editors list (link) - ^ Hake, Laura; Connor, Clare (2008). "Genetic Mechanisms of Sex Determination | Learn Science at Scitable". www.nature.com. Retrieved 2015-10-16.
- ^ Nussbaum, Robert L; McInnes, Roderick R; Willard, Huntington F (2015). Thompson & Thompson Genetics in Medicine. Canada: ELSEVIER. p. 98-101. ISBN 978-1-4377-0696-3.