Autosome

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An autosome is any chromosome that is not a sex chromosome. [1] The members of an autosome pair in a diploid cell have the same morphology, unlike those in allosomal (sex chromosome) pairs, which may have different structures. The DNA in autosomes is collectively known as atDNA or auDNA. [2]

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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 labelled 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 Salome combinations,[ clarification needed ] are known to occur and usually cause developmental abnormalities.

Autosomes still contain sexual determination genes even though they are not sex chromosomes. For example, the SRY gene on the Y chromosome encodes the transcription factor TDF and is vital for male sex determination during development. TDF functions by activating the SOX9 gene on chromosome 17, so mutations of the SOX9 gene can cause humans with an ordinary Y chromosome to develop as females. [4]

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). [5] 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. [6]

Karyotype of human chromosomes
Female (XX)Male (XY)
PLoSBiol3.5.Fig7ChromosomesAluFish.jpg
Human male karyotype.gif
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.

Autosomal genetic disorders

An illustration of the inheritance pattern and phenotypic effects of an autosomal recessive gene. Autosomal recessive inheritance.gif
An illustration of the inheritance pattern and phenotypic effects of an autosomal recessive gene.

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. [7] These disorders manifest in and are passed on by either sex with equal frequency. [7] [8] 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, [9] and fetuses with aneuploidy of gene-poor chromosomes—such as chromosome 21— are still miscarried over 23% of the time. [10] 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, which is caused by possessing three copies of chromosome 21 instead of the usual two. [9]

Partial aneuploidy can also occur as a result of unbalanced translocations during meiosis. [11] 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. [12] [13] Unlike single gene disorders, diseases caused by aneuploidy are the result of improper gene dosage, not nonfunctional gene product. [14]

See also

Related Research Articles

An allele is a variation of the same sequence of nucleotides at the same place on a long DNA molecule, as described in leading textbooks on genetics and evolution. The word is a short form of "allelomorph".

<span class="mw-page-title-main">Genetic disorder</span> Health problem caused by one or more abnormalities in the genome

A genetic disorder is a health problem caused by one or more abnormalities in the genome. It can be caused by a mutation in a single gene (monogenic) or multiple genes (polygenic) or by a chromosomal abnormality. Although polygenic disorders are the most common, the term is mostly used when discussing disorders with a single genetic cause, either in a gene or chromosome. The mutation responsible can occur spontaneously before embryonic development, or it can be inherited from two parents who are carriers of a faulty gene or from a parent with the disorder. When the genetic disorder is inherited from one or both parents, it is also classified as a hereditary disease. Some disorders are caused by a mutation on the X chromosome and have X-linked inheritance. Very few disorders are inherited on the Y chromosome or mitochondrial DNA.

The genotype of an organism is its complete set of genetic material. Genotype can also be used to refer to the alleles or variants an individual carries in a particular gene or genetic location. The number of alleles an individual can have in a specific gene depends on the number of copies of each chromosome found in that species, also referred to as ploidy. In diploid species like humans, two full sets of chromosomes are present, meaning each individual has two alleles for any given gene. If both alleles are the same, the genotype is referred to as homozygous. If the alleles are different, the genotype is referred to as heterozygous.

<span class="mw-page-title-main">Dominance (genetics)</span> One gene variant masking the effect of another in the other copy of the gene

In genetics, dominance is the phenomenon of one variant (allele) of a gene on a chromosome masking or overriding the effect of a different variant of the same gene on the other copy of the chromosome. The first variant is termed dominant and the second is called recessive. This state of having two different variants of the same gene on each chromosome is originally caused by a mutation in one of the genes, either new or inherited. The terms autosomal dominant or autosomal recessive are used to describe gene variants on non-sex chromosomes (autosomes) and their associated traits, while those on sex chromosomes (allosomes) are termed X-linked dominant, X-linked recessive or Y-linked; these have an inheritance and presentation pattern that depends on the sex of both the parent and the child. Since there is only one copy of the Y chromosome, Y-linked traits cannot be dominant or recessive. Additionally, there are other forms of dominance, such as incomplete dominance, in which a gene variant has a partial effect compared to when it is present on both chromosomes, and co-dominance, in which different variants on each chromosome both show their associated traits.

<span class="mw-page-title-main">Aneuploidy</span> Presence of an abnormal number of chromosomes in a cell

Aneuploidy is the presence of an abnormal number of chromosomes in a cell, for example a human cell having 45 or 47 chromosomes instead of the usual 46. It does not include a difference of one or more complete sets of chromosomes. A cell with any number of complete chromosome sets is called a euploid cell.

<span class="mw-page-title-main">Homologous chromosome</span> Chromosomes that pair in fertilization

A couple of homologous chromosomes, or homologs, are a set of one maternal and one paternal chromosome that pair up with each other inside a cell during fertilization. Homologs have the same genes in the same loci where they provide points along each chromosome which enable a pair of chromosomes to align correctly with each other before separating during meiosis. This is the basis for Mendelian inheritance which characterizes inheritance patterns of genetic material from an organism to its offspring parent developmental cell at the given time and area.

<span class="mw-page-title-main">Sex linkage</span> Sex-specific patterns of inheritance

Sex linked describes the sex-specific reading patterns of inheritance and presentation when a gene mutation (allele) is present on a sex chromosome (allosome) rather than a non-sex chromosome (autosome). In humans, these are termed X-linked recessive, X-linked dominant and Y-linked. The inheritance and presentation of all three differ depending on the sex of both the parent and the child. This makes them characteristically different from autosomal dominance and recessiveness.

<span class="mw-page-title-main">Non-Mendelian inheritance</span> Type of pattern of inheritance

Non-Mendelian inheritance is any pattern in which traits do not segregate in accordance with Mendel's laws. These laws describe the inheritance of traits linked to single genes on chromosomes in the nucleus. In Mendelian inheritance, each parent contributes one of two possible alleles for a trait. If the genotypes of both parents in a genetic cross are known, Mendel's laws can be used to determine the distribution of phenotypes expected for the population of offspring. There are several situations in which the proportions of phenotypes observed in the progeny do not match the predicted values.

<span class="mw-page-title-main">Human genetics</span> Study of inheritance as it occurs in human beings

Human genetics is the study of inheritance as it occurs in human beings. Human genetics encompasses a variety of overlapping fields including: classical genetics, cytogenetics, molecular genetics, biochemical genetics, genomics, population genetics, developmental genetics, clinical genetics, and genetic counseling.

Genetics, a discipline of biology, is the science of heredity and variation in living organisms.

<span class="mw-page-title-main">Mulibrey nanism</span> Medical condition

Mulibrey nanism is a rare autosomal recessive congenital disorder. It causes severe growth failure along with abnormalities of the heart, muscle, liver, brain and eye. TRIM37 is responsible for various cellular functions including developmental patterning.

<span class="mw-page-title-main">Short-chain acyl-coenzyme A dehydrogenase deficiency</span> Medical condition

Short-chain acyl-coenzyme A dehydrogenase deficiency (SCADD) is an autosomal recessive fatty acid oxidation disorder which affects enzymes required to break down a certain group of fats called short chain fatty acids.

<span class="mw-page-title-main">Autosomal recessive multiple epiphyseal dysplasia</span> Medical condition

Autosomal recessive multiple epiphyseal dysplasia (ARMED), also called epiphyseal dysplasia, multiple, 4 (EDM4), multiple epiphyseal dysplasia with clubfoot or –with bilayered patellae, is an autosomal recessive congenital disorder affecting cartilage and bone development. The disorder has relatively mild signs and symptoms, including joint pain, scoliosis, and malformations of the hands, feet, and knees.

A chromosomal abnormality, chromosomal anomaly, chromosomal aberration, chromosomal mutation, or chromosomal disorder, is a missing, extra, or irregular portion of chromosomal DNA. These can occur in the form of numerical abnormalities, where there is an atypical number of chromosomes, or as structural abnormalities, where one or more individual chromosomes are altered. Chromosome mutation was formerly used in a strict sense to mean a change in a chromosomal segment, involving more than one gene. Chromosome anomalies usually occur when there is an error in cell division following meiosis or mitosis. Chromosome abnormalities may be detected or confirmed by comparing an individual's karyotype, or full set of chromosomes, to a typical karyotype for the species via genetic testing.

<span class="mw-page-title-main">Sex chromosome</span> Chromosome that differs from an ordinary autosome in form, size, and behavior

A sex chromosome is a chromosome that differs from an ordinary autosome in form, size, and behavior. The human sex chromosomes, a typical pair of mammal allosomes, carry the genes that determine the sex of an individual created in sexual reproduction. Autosomes differ from allosomes because 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 following outline is provided as an overview of and topical guide to genetics:

<span class="mw-page-title-main">Hereditary carrier</span> Organism with a recessive genetic allele that does not display the recessive trait

A hereditary carrier, is a person or other organism that has inherited a recessive allele for a genetic trait or mutation but usually does not display that trait or show symptoms of the disease. Carriers are, however, able to pass the allele onto their offspring, who may then express the genetic trait.

<span class="mw-page-title-main">Woodhouse–Sakati syndrome</span> Medical condition

Woodhouse–Sakati syndrome, is a rare autosomal recessive multisystem disorder which causes malformations throughout the body, and deficiencies affecting the endocrine system.

<span class="mw-page-title-main">Gillespie syndrome</span> Medical condition

Gillespie syndrome, also called aniridia, cerebellar ataxia and mental deficiency, is a rare genetic disorder. The disorder is characterized by partial aniridia, ataxia, and, in most cases, intellectual disability. It is heterogeneous, inherited in either an autosomal dominant or autosomal recessive manner. Gillespie syndrome was first described by American ophthalmologist Fredrick Gillespie in 1965.

<span class="mw-page-title-main">Lethal congenital contracture syndrome</span> Medical condition

Lethal congenital contracture syndrome 1 (LCCS1), also called Multiple contracture syndrome, Finnish type, is an autosomal recessive genetic disorder characterized by total immobility of a fetus, detectable at around the 13th week of pregnancy. LCCS1 invariably leads to prenatal death before the 32nd gestational week. LCCS1 is one of 40 Finnish heritage diseases. It was first described in 1985 and since then, approximately 70 cases have been diagnosed.

References

  1. ↑ Griffiths, Anthony J. F. (1999). An Introduction to genetic analysis. New York: W.H. Freeman. ISBN   978-0-7167-3771-1.
  2. ↑ "Autosomal DNA - ISOGG Wiki". www.isogg.org. Archived from the original on 21 August 2017. Retrieved 28 April 2018.
  3. ↑ "Autosome Definition(s)". Genetics Home Reference. Archived from the original on 2 January 2016. Retrieved 28 April 2018.
  4. ↑ 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.
  5. ↑ "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.
  6. ↑ 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.
  7. 1 2 "human genetic disease". Encyclopædia Britannica. Archived from the original on 2015-10-13. Retrieved 2015-10-16.
  8. ↑ Chial, Heidi (2008). "Mendelian Genetics: Patterns of Inheritance and Single-Gene Disorders". Nature Education. 1 (1): 63.
  9. 1 2 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.
  10. ↑ 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.
  11. ↑ "Translocation - Glossary Entry". Genetics Home Reference. 2015-11-02. Archived from the original on 2015-12-09. Retrieved 2015-11-08.
  12. ↑ 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.
  13. ↑ 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.
  14. ↑ 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.
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