An autosome is a chromosome that is not an allosome (a sex chromosome). The members of an autosome pair in a diploid cell have the same morphology, unlike those in allosome pairs which may have different structures. The DNA in autosomes is collectively known as atDNA or auDNA.
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. 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.
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.
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). 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.
|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.|
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. These disorders manifest in and are passed on by either sex with equal frequency. 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, and fetuses with aneuploidy of gene-poor chromosomes—such as chromosome 21— are still miscarried over 23% of the time. 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.
Partial aneuploidy can also occur as a result of unbalanced translocations during meiosis. 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. Unlike single gene disorders, diseases caused by aneuploidy are the result of improper gene dosage, not nonfunctional gene product.
Adamorobe Sign Language or Adasl is a village sign language used in Adamorobe, an Akan village in eastern Ghana. It is used by about 30 deaf and 1370 hearing people (2003).The Adamorobe community is notable for its unusually high incidence of hereditary deafness (genetic recessive autosome). Currently (2012) about 1.1% of the total population is deaf, but the percentage was as high as 11% in 1961 before the local chief instituted a policy prohibiting deaf people to marry other deaf. Deaf people are fully incorporated into the community.
Under these circumstances, AdaSL has developed as an indigenous sign language, fully independent from the country's standard Ghanaian Sign Language (which is related to American Sign Language). AdaSL is a shared sign language which differs from urban sign languages such as Ghanaian Sign Language because the majority of speakers of a shared sign language aren't actually deaf. National sign languages usually emerge for the purpose of use by deaf individuals such as those attending schools specifically for the deaf. This important feature of shared sign languages alters the way it is maintained, developed, and shared. A historical example of a shared signing community is the island Martha's Vineyard (Martha's Vineyard Sign Language).AdaSL shares signs and prosodic features with some other sign languages in the region, such as Bura Sign Language, but it has been suggested these similarities are due to culturally shared gestures rather than a genetic relationship. AdaSL has features that set it apart from the sign languages of large deaf communities studied so far, including the absence of the type of classifier construction that expresses motion or location (sometimes called "entity classifiers"). Instead, AdaSL uses several types of serial verb constructions also found in the surrounding spoken language, Akan. Frishberg suggests that AdaSL may be related to the "gestural trade jargon used in the markets throughout West Africa". Thus AdaSL provides an interesting domain for research on cross-linguistic sign languages.
For over a decade, the deaf children of the village have attended a boarding school in Mampong-Akuapem, where the ASL based Ghanaian Sign Language is used. As a consequence, this language has become the first language of these children and their command of AdaSL is decreasing. This is likely to lead to a complete shift of the deaf community in Adamorobe to Ghanaian Sign Language. As such, AdaSL is an endangered sign language.Adenosine deaminase deficiency
Adenosine deaminase deficiency (also called ADA deficiency or ADA-SCID) is an autosomal recessive metabolic disorder that causes immunodeficiency. It occurs in fewer than one in 100,000 live births worldwide.
It accounts for about 15% of all cases of severe combined immunodeficiency (SCID).
ADA deficiency may be present in infancy, childhood, adolescence, or adulthood. Age of onset and severity is related to some 29 known genotypes associated with the disorder.Autosomal recessive multiple epiphyseal dysplasia
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.Some affected individuals are born with an inward- and downward-turning foot (a clubfoot). An abnormality of the kneecap called a double-layered patella is also relatively common. Although some people with recessive multiple epiphyseal dysplasia have short stature as adults, most are of normal height. The incidence is unknown as many cases are not diagnosed due to mild symptoms.Carnosinemia
Carnosinemia, also called carnosinase deficiency or aminoacyl-histidine dipeptidase deficiency, is a rare autosomal recessive metabolic disorder caused by a deficiency of carnosinase', a dipeptidase (a type of enzyme that splits dipeptides into their two amino acid constituents).Carnosine is a dipeptide composed of beta-alanine and histidine, and is found in skeletal muscle and cells of the nervous system. This disorder results in an excess of carnosine in the urine, cerebrospinal fluid, blood, and nervous tissue. Neurological disorders associated with a deficiency of carnosinase, and the resulting carnosinemia ("carnosine in the blood") are common.Cerebrotendineous xanthomatosis
Cerebrotendineous xanthomatosis or cerebrotendinous xanthomatosis (CTX), also called cerebral cholesterosis, is an autosomal recessive form of xanthomatosis. It falls within a group of genetic disorders called the leukodystrophies.Chromosome 21
Chromosome 21 is one of the 23 pairs of chromosomes in humans. Chromosome 21 is both the smallest human autosome and chromosome, with 48 million nucleotides (the building material of DNA) representing about 1.5 percent of the total DNA in cells. Most people have two copies of chromosome 21, while those with three copies of chromosome 21 have Down syndrome, also called "trisomy 21".
Researchers working on the Human Genome Project announced in May 2000 that they had determined the sequence of base pairs that make up this chromosome. Chromosome 21 was the second human chromosome to be fully sequenced, after chromosome 22.Congenital stromal corneal dystrophy
Congenital stromal corneal dystrophy (CSCD), also called Witschel dystrophy, is an extremely rare, autosomal dominant form of corneal dystrophy. Only 4 families have been reported to have the disease by 2009. The main features of the disease are numerous opaque flaky or feathery areas of clouding in the stroma that multiply with age and eventually preclude visibility of the endothelium. Strabismus or primary open angle glaucoma was noted in some of the patients. Thickness of the cornea stays the same, Descemet's membrane and endothelium are relatively unaffected, but the fibrills of collagen that constitute stromal lamellae are reduced in diameter and lamellae themselves are packed significantly more tightly.Gene dosage
Gene dosage is the number of copies of a particular gene present in a genome. Gene dosage is known to be related to the amount of gene product the cell is able to express, however, amount of gene product produced in a cell is more commonly dependent on regulation of gene expression. Nonetheless, changes in gene dosage (copy number variations) due to gene insertions or deletions can have significant phenotypic consequences.In eukaryotes, most genes found in the cell are expressed as autosomal genes (see autosome) and are found in two copies, alterations to this two-copy gene dosage is significantly associated with quantitative or qualitative phenotype traits and is linked to many genetic health problems such as those associated with spinal muscular atrophy and Down syndrome. In Down syndrome, the gene expression on chromosome 21 has increased 50%, and this results in significant health and mental disabilities (1 in 800 human live births have Down syndrome).Prokaryotes reproduce through asexual reproduction, usually by binary fission. The bacterial chromosome is present only in one copy per cell, but there can still be variation in gene dosage due to DNA replication which starts at the origin of replication and ends at the termination site. The genes that are closer to the origin site would be replicated first and would consequently be present in two copies in the cell for a longer time than the genes that are closer to the termination site. These slight gene dosage differences are responsible for variation in gene expression depending on the position on the chromosome.Keratolytic winter erythema
Keratolytic Winter erythema (also known as Oudtshoorn disease or Oudtshoorn skin) is a rare autosomal dominant skin disease of unknown cause which causes redness and peeling of the skin on the palms and soles. Onset, increased prominence and severity usually occurs during winter. It is a type of genodermatosis.The name "Oudtshoorn skin" derives from the town of Oudtshoorn in the Western Cape province of South Africa, where the disorder was first described. It is one of several genetic disorders known to be highly prevalent among the Afrikaner population.Naegeli–Franceschetti–Jadassohn syndrome
Naegeli–Franceschetti–Jadassohn syndrome (NFJS), also known as chromatophore nevus of Naegeli and Naegeli syndrome, is a rare autosomal dominant form of ectodermal dysplasia, characterized by reticular skin pigmentation, diminished function of the sweat glands, the absence of teeth and hyperkeratosis of the palms and soles. One of the most striking features is the absence of fingerprint lines on the fingers.
Naegeli syndrome is similar to dermatopathia pigmentosa reticularis, both of which are caused by a specific defect in the keratin 14 protein.Opsismodysplasia
Opsismodysplasia is a type of skeletal dysplasia (a bone disease that interferes with bone development) first described by Zonana and associates in 1977, and designated under its current name by Maroteaux (1984). Derived from the Greek opsismos ("late"), the name "opsismodysplasia" describes a delay in bone maturation. In addition to this delay, the disorder is characterized by micromelia (short or undersized bones), particularly of the hands and feet, delay of ossification (bone cell formation), platyspondyly (flattened vertebrae), irregular metaphyses, an array of facial aberrations and respiratory distress related to chronic infection. Opsismodysplasia is congenital, being apparent at birth. It has a variable mortality, with some affected individuals living to adulthood. The disorder is rare, with an incidence of less than 1 per 1,000,000 worldwide. It is inherited in an autosomal recessive pattern, which means the defective (mutated) gene that causes the disorder is located on an autosome, and the disorder occurs when two copies of this defective gene are inherited. No specific gene has been found to be associated with the disorder. It is similar to spondylometaphyseal dysplasia, Sedaghatian type.Purine nucleoside phosphorylase deficiency
Purine nucleoside phosphorylase deficiency, often called PNP-deficiency, is a rare autosomal recessive metabolic disorder which results in immunodeficiency.Salla disease
Salla disease (SD), also called sialic acid storage disease or Finnish type sialuria, is an autosomal recessive lysosomal storage disease characterized by early physical impairment and intellectual disability. It was first described in 1979, after Salla, a municipality in Finnish Lapland. Salla disease is one of 40 Finnish heritage diseases and affects approximately 130 individuals, mainly from Finland and Sweden.Sarcosinemia
Sarcosinemia (SAR), also called hypersarcosinemia and SARDH deficiency, is a rare autosomal recessive metabolic disorder characterized by an increased concentration of sarcosine in blood plasma and urine ("sarcosinuria"). It can result from an inborn error of sarcosine metabolism, or from severe folate deficiency related to the folate requirement for the conversion of sarcosine to glycine. It is thought to be a relatively benign condition.Sex chromosome
An allosome (also referred to as a sex chromosome, heterotypical chromosome, heterochromosome, or idiochromosome) is a chromosome that differs from an ordinary autosome in form, size, and behavior. The human sex chromosomes, a typical pair of mammal allosomes, 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.
Nettie Stevens and Edmund Beecher Wilson both independently discovered sex chromosomes in 1905. However, Stevens is credited for discovering them earlier than Wilson.Sex linkage
Sex linkage describes the particular patterns of inheritance and trait presentation when a mutated gene (an allele) is present on a sex chromosome (an allosome) rather than a non-sex chromosome (an autosome). They are characteristically different from the autosomal forms of dominance and recessiveness. Since humans have several times as many genes on the female X chromosome than on the male Y chromosome, X-linked traits are much more common than Y-linked traits. Additionally, there are more X-linked recessive conditions than X-linked dominant, and X-linked recessive conditions affect males much more commonly due to males only having the one X chromosome required for the condition to present.
In humans, X-linked traits are inherited from a carrier or affected mother or from an affected father. In X-linked recessive conditions, a son born to an unaffected father and a carrier mother has a 50% chance of inheriting the mother's X chromosome carrying the mutant allele and presenting with the condition. A daughter on the other hand has a 50% chance of being a carrier, however a fraction of carriers may display a milder (or even full) form of the condition due to their body's normal X-inactivation process preferably inactivating a certain parent's X chromosome (the father's in this case), a phenomenon known as skewed X-inactivation. If the condition is dominant, or if the father is also affected, the daughter has a 50% chance of being affected, with an additional 50% chance of being a carrier in the second case. A son born to an affected father and a non-carrier mother will always be unaffected due to not inheriting the father's X chromosome. A daughter on the other hand will always be a carrier (some of which may present with symptoms due to aforementioned skewed X-inactivation), unless the condition is dominant, in which case she will always be affected. There are a few Y-linked traits; these are inherited by sons from their father and are always expressed.
The incidence of X-linked recessive phenotypes in females is the square of that in males: for example, if 1 in 20 males in a human population are red-green color blind, then 1 in 400 females in the population are expected to be color-blind (1/20)*(1/20).
The inheritance patterns are different in animals which use different sex-determination systems. In the ZW sex-determination system used by birds, the mammalian pattern is reversed since the male is the homogametic sex (ZZ) and the female is heterogametic (ZW).
In classical genetics, a mating experiment called a reciprocal cross is performed to test if an animal's trait is sex-linked.Tietz syndrome
Tietz syndrome, also called Tietz albinism-deafness syndrome or albinism and deafness of Tietz, is an autosomal dominant congenital disorder characterized by deafness and leucism. It is caused by a mutation in the microphthalmia-associated transcription factor (MITF) gene. Tietz syndrome was first described in 1963 by Walter Tietz (1927–2003) a German Physician working in California.Woodhouse–Sakati syndrome
Woodhouse–Sakati syndrome, also called hypogonadism, alopecia, diabetes mellitus, intellectual disability and extrapyramidal syndrome, is a rare autosomal recessive multisystem disorder which causes malformations throughout the body, and deficiencies affecting the endocrine system.Worth syndrome
Worth syndrome, also known as benign form of Worth hyperostosis corticalis generalisata with torus platinus, autosomal dominant osteosclerosis, autosomal dominant endosteal hyperostosis or Worth disease, is a rare autosomal dominant congenital disorder that is caused by a mutation in the LRP5 gene. It is characterized by increased bone density and benign bony structures on the palate.