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An autosome is any
chromosome A chromosome is a long DNA molecule with part or all of the genome, genetic material of an organism. Most eukaryotic chromosomes include packaging proteins called histones which, aided by Chaperone (protein), chaperone proteins, bind to and ...

chromosome
that is not a sex chromosome (an
allosome A sex chromosome (also referred to as an allosome, heterotypical chromosome, gonosome, heterochromosome, or idiochromosome) is a chromosome A chromosome is a long DNA molecule with part or all of the genome, genetic material of an organi ...
). The members of an autosome pair in a
diploid Ploidy () is the number of complete sets of chromosomes in a cell (biology), cell, and hence the number of possible alleles for Autosome, autosomal and Pseudoautosomal region, pseudoautosomal genes. Sets of chromosomes refer to the number of mate ...
cell have the same morphology, unlike those in allosome pairs which may have different structures. The
DNA Deoxyribonucleic acid (; DNA) is a molecule File:Pentacene on Ni(111) STM.jpg, A scanning tunneling microscopy image of pentacene molecules, which consist of linear chains of five carbon rings. A molecule is an electrically neutral gro ...

DNA
in autosomes is collectively known as atDNA or auDNA. For example,
human Humans (''Homo sapiens'') are the most abundant and widespread species In biology, a species is the basic unit of biological classification, classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A speci ...

human
s have a
diploid Ploidy () is the number of complete sets of chromosomes in a cell (biology), cell, and hence the number of possible alleles for Autosome, autosomal and Pseudoautosomal region, pseudoautosomal genes. Sets of chromosomes refer to the number of mate ...
genome In the fields of molecular biology Molecular biology is the branch of biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, M ...

genome
that usually contains 22 pairs of autosomes and one
allosome A sex chromosome (also referred to as an allosome, heterotypical chromosome, gonosome, heterochromosome, or idiochromosome) is a chromosome A chromosome is a long DNA molecule with part or all of the genome, genetic material of an organi ...
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 chromosome The X chromosome is one of the two sex-determining chromosome A chromosome is a long DNA Deoxyribonucleic acid (; DNA) is a molecule File:Pentacene on Ni(111) STM.jpg, A scanning tunneling microscopy image of pentacene molecul ...

X chromosome
s in females or one X and one
Y chromosome The Y chromosome is one of two sex chromosome A chromosome is a long DNA molecule with part or all of the genome, genetic material of an organism. Most eukaryotic chromosomes include packaging proteins called histones which, aided by Chaper ...
in males. Unusual combinations of
XYY
XYY
, XXY, XXX,
XXXX
XXXX
, XXXXX or
XXYY
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 Testis-determining factor (TDF), also known as sex-determining region Y (SRY) protein, is a DNA-binding protein protein complex with DNA s (blue). These proteins' basic amino acids bind to the acidic phosphate groups on DNA. repressor heli ...
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 Transcription factor SOX-9 is a protein Proteins are large s and s that comprise one or more long chains of . Proteins perform a vast array of functions within organisms, including , , , providing and , and from one location to another. P ...
gene on
chromosome 17 Chromosome 17 is one of the 23 pairs of chromosomes in humans. People normally have two copies of this chromosome. Chromosome 17 spans more than 83 million base pairs (the building material of DNA) and represents between 2.5 and 3% of the total DNA ...
, so mutations of the
SOX9 Transcription factor SOX-9 is a protein Proteins are large s and s that comprise one or more long chains of . Proteins perform a vast array of functions within organisms, including , , , providing and , and from one location to another. P ...
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 Metaphase () is a stage of mitosis In cell biology Cell biology (also cellular biology or cytology) is a branch of biology Biology is the natural science that studies life and living organisms, including their anatomy, physical s ...

metaphase
or
prometaphase Prometaphase is the phase of mitosis following prophase and preceding metaphase, in eukaryote, eukaryotic Somatic (biology), somatic Cell (biology), cells. In prometaphase, the nuclear membrane breaks apart into numerous "membrane vesicles", a ...

prometaphase
and then staining them with a type of dye (most commonly,
Giemsa Giemsa stain (), named after German chemist and bacteriologist Gustav Giemsa Gustav Giemsa (; November 20, 1867 – June 10, 1948) was a German chemist and bacteriologist who was a native of Medar-Blechhammer (now part of the city Kędzierzyn-Ko ...
). These chromosomes are typically viewed as
karyogram Karyotyping is the process by which photographs of chromosome A chromosome is a long DNA molecule with part or all of the genetic material of an organism. Most eukaryotic chromosomes include packaging proteins called histones which, aided ...
s for easy comparison. Clinical geneticists can compare the karyogram of an individual to a reference karyogram to discover the cytogenetic basis of certain
phenotype In genetics Genetics is a branch of biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, Molecular biology, molecular inter ...

phenotype
s. For example, the karyogram of someone with
Patau Syndrome Patau syndrome is a syndrome caused by a chromosomal abnormality, in which some or all of the cells of the body contain extra genetic material from chromosome 13. The extra genetic material disrupts normal development, causing multiple and comp ...
would show that they possess three copies of
chromosome 13 Chromosome 13 is one of the 23 pairs of chromosome A chromosome is a long DNA molecule with part or all of the genetic material of an organism. Most eukaryotic chromosomes include packaging proteins called histones which, aided by chaper ...
. 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.


Autosomal genetic disorders

Autosomal genetic disorders can arise due to a number of causes, some of the most common being
nondisjunction Nondisjunction is the failure of homologous chromosomes 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 sam ...
in parental germ cells or
Mendelian inheritance Mendelian inheritance is a type of biological Biology is the natural science Natural science is a branch of science Science (from the Latin word ''scientia'', meaning "knowledge") is a systematic enterprise that Scientific me ...

Mendelian inheritance
of deleterious alleles from parents. Autosomal genetic disorders which exhibit Mendelian inheritance can be inherited either in an
autosomal dominant In genetics, dominance is the phenomenon of one variant (allele) of a gene on a chromosome masking or overriding the Phenotype, effect of a different variant of the same gene on Homologous chromosome, the other copy of the chromosome. The first ...

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 An allele (, ; ; modern formation from Greek ἄλλος ''állos'', "other") is one of two, or more, forms of a given gene In biology, a gene (from ''genos'' "...Wilhelm Johannsen coined the word gene to describe the Mendelian_inheritance ...
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
heterozygote Zygosity (the noun, zygote A zygote (from Greek ζυγωτός ''zygōtos'' "joined" or "yoked", from ζυγοῦν ''zygoun'' "to join" or "to yoke") is a eukaryotic cell formed by a fertilization event between two gamete A gamete ( /ˈ ...
s) for the condition. Autosomal
aneuploidy Aneuploidy is the presence of an abnormal number of chromosomes in a cell (biology), 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 ploidy#Haploid and monoploid, c ...
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 Chromosome 1 is the designation for the largest human chromosome. Humans have two copies of chromosome 1, as they do with all of the autosome An autosome is any chromosome that is not a sex chromosome (an allosome). The members of an autosome ...
—never survive to term, and fetuses with aneuploidy of gene-poor chromosomes—such as
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 base pairs (the building material of DNA) representing about 1.5 percent of the total DNA in cell (biol ...
— 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 Down syndrome or Down's syndrome, also known as trisomy 21, is a genetic disorder A genetic disorder is a health problem caused by one or more abnormalities in the genome In the fields of molecular biology and genetics Gen ...
, which is caused by possessing three copies of
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 base pairs (the building material of DNA) representing about 1.5 percent of the total DNA in cell (biol ...
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 Cancer is a group of diseases involving abnormal cell growth with the potential to invade or spread to other parts of the body. These contrast with benign tumor A benign tumor is a mass of cells Cell most often refers to: * Cell (biolo ...

cancer
to
schizophrenia Schizophrenia is a mental disorder A mental disorder, also called a mental illness or psychiatric disorder, is a behavioral or mental pattern that causes significant distress or impairment of personal functioning. Such features may b ...

schizophrenia
. Unlike single gene disorders, diseases caused by aneuploidy are the result of improper
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, the amount of gene product produced in a cell is more commonly depen ...
, not nonfunctional gene product.


See also

*
Aneuploidy Aneuploidy is the presence of an abnormal number of chromosomes in a cell (biology), 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 ploidy#Haploid and monoploid, c ...
(abnormal number of chromosomes) *
Autosomal dominant In genetics, dominance is the phenomenon of one variant (allele) of a gene on a chromosome masking or overriding the Phenotype, effect of a different variant of the same gene on Homologous chromosome, the other copy of the chromosome. The first ...

Autosomal dominant
*
Autosomal recessive In genetics Genetics is a branch of biology concerned with the study of genes, genetic variation, and heredity in organisms.Hartl D, Jones E (2005) Though heredity had been observed for millennia, Gregor Mendel, Moravia, Moravian scientist ...

Autosomal recessive
*
Homologous chromosome A couple of homologous chromosomes, or homologs, are a set of one maternal and one paternal chromosome A chromosome is a long DNA The structure of part of a DNA double helix Deoxyribonucleic acid (; DNA) is a molecule File:Pen ...
*
Pseudoautosomal region Image:A region in the pseudoautosomal region of the short arms of the X- and Y-chromosome.jpg, Detail of a human metaphase spread. A region in the pseudoautosomal region of the short arms of the X chromosome (left) and the Y chromosome (top right) w ...

Pseudoautosomal region
*
XY sex-determination system The XY sex-determination system is a sex-determination system A sex-determination system is a biological system that determines the development of sexual characteristics in an organism In biology, an organism (from Ancient Greek, Gree ...
*
Genetic disorder A genetic disorder is a health problem caused by one or more abnormalities in the genome In the fields of molecular biology Molecular biology is the branch of biology Biology is the natural science that studies life and li ...


References

{{Chromosomes Chromosomes Cytogenetics