What is chromosome 6?

Humans normally have 46 chromosomes in each cell, divided into 23 pairs. Two copies of chromosome 6, one copy inherited from each parent, form one of the pairs. Chromosome 6 spans about 171 million DNA building blocks (base pairs) and represents between 5.5 and 6 percent of the total DNA in cells.
Identifying genes on each chromosome is an active area of genetic research. Because researchers use different approaches to predict the number of genes on each chromosome, the estimated number of genes varies. Chromosome 6 likely contains 1,000 to 1,100 genes that provide instructions for making proteins. These proteins perform a variety of different roles in the body.
Genes on chromosome 6 are among the estimated 20,000 to 25,000 total genes in the human genome.

How are changes in chromosome 6 related to health conditions?

Many genetic conditions are related to changes in particular genes on chromosome 6. This list of disorders associated with genes on chromosome 6 provides links to additional information.
Changes in the structure or number of copies of a chromosome can also cause problems with health and development. The following chromosomal conditions are associated with such changes in chromosome 6.

cancers

Duplications of genetic material in the short (p) arm of chromosome 6 have been associated with the growth and spread of several types of cancer. These duplications are somatic, which means they are acquired during a person's lifetime and are present only in certain cells. Researchers believe that some of the genes in the duplicated region on chromosome 6p are oncogenes. Oncogenes play roles in several critical cell functions, including cell division, the maturation of cells to carry out specific functions (cell differentiation), and the self-destruction of cells (apoptosis). When mutated, oncogenes have the potential to cause normal cells to become cancerous. The presence of extra copies of the oncogenes may allow cells to grow and divide in an uncontrolled way, leading to the progression and spread of cancer.

6q24-related transient neonatal diabetes mellitus

6q24-related transient neonatal diabetes mellitus, a type of diabetes that occurs in infants, is caused by the overactivity (overexpression) of certain genes in a region of the long (q) arm of chromosome 6 called 6q24. People inherit two copies of their genes, one from their mother and one from their father. Usually both copies of each gene are active, or "turned on," in cells. In some cases, however, only one of the two copies is normally turned on. Which copy is active depends on the parent of origin: some genes are normally active only when they are inherited from a person's father; others are active only when inherited from a person's mother. This phenomenon is known as genomic imprinting.
The 6q24 region includes paternally expressed imprinted genes, which means that normally only the copy of each gene that comes from the father is active. The copy of each gene that comes from the mother is inactivated (silenced) by a mechanism called methylation.
There are three ways that overexpression of paternally expressed imprinted genes in the 6q24 region can occur. About 40 percent of cases of 6q24-related transient neonatal diabetes mellitus are caused by a genetic change known as paternal uniparental disomy (UPD) of chromosome 6. In paternal UPD, people inherit both copies of the affected chromosome from their father instead of one copy from each parent. Paternal UPD causes people to have two active copies of paternally expressed imprinted genes, rather than one active copy from the father and one inactive copy from the mother.
Another 40 percent of cases of 6q24-related transient neonatal diabetes mellitus occur when the copy of chromosome 6 that comes from the father has a duplication of genetic material including the paternally expressed imprinted genes in the 6q24 region.
The third mechanism by which overexpression of genes in the 6q24 region can occur is by impaired silencing of the maternal copy of the genes (maternal hypomethylation). Approximately 20 percent of cases of 6q24-related transient neonatal diabetes mellitus are caused by maternal hypomethylation. Some people with this disorder have a genetic change in the maternal copy of the 6q24 region that prevents genes in that region from being silenced. Other affected individuals have a more generalized impairment of gene silencing involving many imprinted regions, called hypomethylation of imprinted loci (HIL). Because HIL can cause overexpression of many genes, this mechanism may account for the additional health problems that occur in some people with 6q24-related transient neonatal diabetes mellitus.
It is not well understood how overexpression of genes in the 6q24 region causes 6q24-related transient neonatal diabetes mellitus and why the condition improves after infancy. This form of diabetes is characterized by high blood sugar levels (hyperglycemia) resulting from a shortage of the hormone insulin. Insulin controls how much glucose (a type of sugar) is passed from the blood into cells for conversion to energy.
The protein produced from one gene in the 6q24 region may help control insulin secretion by beta cells in the pancreas. In addition, overexpression of this protein has been shown to stop the cycle of cell division and lead to the self-destruction of cells (apoptosis). Researchers suggest that overexpression of this gene may reduce the number of insulin-secreting beta cells or impair their function in affected individuals.
Lack of sufficient insulin results in the signs and symptoms of diabetes mellitus. In individuals with 6q24-related transient neonatal diabetes mellitus, these signs and symptoms are most likely to occur during times of physiologic stress, including the rapid growth of infancy, childhood illnesses, and pregnancy. Because insulin acts as a growth promoter during early development, a shortage of this hormone may account for the slow growth before birth (intrauterine growth retardation) seen in 6q24-related transient neonatal diabetes mellitus.

other chromosomal conditions

Other changes in the number or structure of chromosome 6 can have a variety of effects, including delayed growth and development, intellectual disability, distinctive facial features, birth defects, and other health problems. Changes to chromosome 6 may include deletions or duplications of genetic material in the short (p) or long (q) arm of the chromosome in each cell, or a circular structure called ring chromosome 6. Ring chromosomes occur when a chromosome breaks in two places and the ends of the chromosome arms fuse together to form a circular structure.

Is there a standard way to diagram chromosome 6?

Geneticists use diagrams called ideograms as a standard representation for chromosomes. Ideograms show a chromosome's relative size and its banding pattern. A banding pattern is the characteristic pattern of dark and light bands that appears when a chromosome is stained with a chemical solution and then viewed under a microscope. These bands are used to describe the location of genes on each chromosome.

What is chromosome 5?

Humans normally have 46 chromosomes in each cell, divided into 23 pairs. Two copies of chromosome 5, one copy inherited from each parent, form one of the pairs. Chromosome 5 spans about 181 million DNA building blocks (base pairs) and represents almost 6 percent of the total DNA in cells.
Identifying genes on each chromosome is an active area of genetic research. Because researchers use different approaches to predict the number of genes on each chromosome, the estimated number of genes varies. Chromosome 5 likely contains about 900 genes that provide instructions for making proteins. These proteins perform a variety of different roles in the body.
Genes on chromosome 5 are among the estimated 20,000 to 25,000 total genes in the human genome.

How are changes in chromosome 5 related to health conditions?

Many genetic conditions are related to changes in particular genes on chromosome 5. This list of disorders associated with genes on chromosome 5 provides links to additional information.
Changes in the structure or number of copies of a chromosome can also cause problems with health and development. The following chromosomal conditions are associated with such changes in chromosome 5.

cancers

Changes in the structure of chromosome 5 are associated with certain forms of cancer and conditions related to cancer. These changes are typically somatic, which means they are acquired during a person's lifetime and are present only in tumor cells. Deletions in the long (q) arm of the chromosome have been identified in a form of blood cancer known as acute myeloid leukemia (AML). These deletions also frequently occur in a disorder called myelodysplastic syndrome, which is a disease of the blood and bone marrow. People with this condition have a low number of red blood cells (anemia) and an increased risk of developing AML. When MDS is associated with a specific deletion in the long arm of chromosome 5, it is known as 5q- (5q minus) syndrome.
Studies suggest that some genes on chromosome 5 play critical roles in the growth and division of cells. When segments of the chromosome are deleted, as in some cases of AML and MDS, these important genes are missing. Without these genes, cells can grow and divide too quickly and in an uncontrolled way. Researchers are working to identify the specific genes on chromosome 5 that are related to AML and MDS.

cri-du-chat syndrome

Cri-du-chat (cat's cry) syndrome is caused by a deletion of the end of the short (p) arm of chromosome 5. This chromosomal change is written as 5p- (5p minus). The signs and symptoms of cri-du-chat syndrome are probably related to the loss of multiple genes in this region. Researchers are working to determine how the loss of these genes leads to the features of the disorder. They have discovered that in people with cri-du-chat syndrome, larger deletions tend to result in more severe intellectual disability and developmental delays than smaller deletions. Researchers have also defined regions of the short arm of chromosome 5 that are associated with particular features of cri-du-chat syndrome. A specific region designated 5p15.3 is associated with a cat-like cry, and a nearby region called 5p15.2 is associated with intellectual disability, small head size (microcephaly), and distinctive facial features.

Crohn disease

Several regions of chromosome 5 have been associated with the risk of developing Crohn disease. For example, a combination of genetic variations in a region of DNA on the long (q) arm of the chromosome (5q31) has been shown to increase a person's chance of developing Crohn disease. Together, these variations are known as the inflammatory bowel disease 5 (IBD5) locus. This region of chromosome 5 contains several related genes that may influence Crohn disease risk, including SLC22A4 and SLC22A5.
Variations in a region of the short (p) arm of chromosome 5 designated 5p13.1 are also associated with Crohn disease risk. Researchers refer to this part of chromosome 5 as a "gene desert" because it contains no known genes; however, it may contain stretches of DNA that help regulate nearby genes such as PTGER4. Research studies are under way to examine a possible connection between the PTGER4 gene and Crohn disease.

PDGFRB-associated chronic eosinophilic leukemia

Translocations involving chromosome 5 are involved in a type of blood cell cancer called PDGFRB-associated chronic eosinophilic leukemia. This condition is characterized by an increased number of eosinophils, a type of white blood cell. The most common translocation that causes this condition fuses part of the PDGFRB gene from chromosome 5 with part of the ETV6 gene from chromosome 12, written as t(5;12)(q31-33;p13). Translocations fusing the PDGFRB gene with one of more than 20 other genes have also been found to cause PDGFRB-associated chronic eosinophilic leukemia, but these other genetic changes are relatively uncommon. These translocations are acquired during a person's lifetime and are present only in cancer cells. This type of genetic change, called a somatic mutation, is not inherited.
The protein produced from the ETV6-PDGFRB fusion gene, called ETV6/PDGFRβ, functions differently than the proteins normally produced from the individual genes. The ETV6 protein normally turns off (represses) gene activity and the PDGFRβ protein plays a role in turning on (activating) signaling pathways. The ETV6/PDGFRβ protein is always turned on, activating signaling pathways and gene activity. When the ETV6-PDGFRB fusion gene mutation occurs in cells that develop into blood cells, the growth of eosinophils (and occasionally other white blood cells, such as neutrophils and mast cells) is poorly controlled, leading to PDGFRB-associated chronic eosinophilic leukemia. It is unclear why eosinophils are preferentially affected by this genetic change.

periventricular heterotopia

In a few cases, abnormalities in chromosome 5 have been associated with periventricular heterotopia, a disorder characterized by abnormal clumps of nerve cells (neurons) around fluid-filled cavities (ventricles) near the center of the brain. In each case, the affected individual had extra genetic material caused by an abnormal duplication of part of this chromosome. It is not known how this duplicated genetic material results in the signs and symptoms of periventricular heterotopia.

other chromosomal conditions

Other changes in the number or structure of chromosome 5 can have a variety of effects, including delayed growth and development, distinctive facial features, birth defects, and other health problems. Changes to chromosome 5 include an extra segment of the short (p) or long (q) arm of the chromosome in each cell (partial trisomy 5p or 5q), a missing segment of the long arm of the chromosome in each cell (partial monosomy 5q), and a circular structure called ring chromosome 5. Ring chromosomes occur when a chromosome breaks in two places and the ends of the chromosome arms fuse together to form a circular structure.

Is there a standard way to diagram chromosome 5?

Geneticists use diagrams called ideograms as a standard representation for chromosomes. Ideograms show a chromosome's relative size and its banding pattern. A banding pattern is the characteristic pattern of dark and light bands that appears when a chromosome is stained with a chemical solution and then viewed under a microscope. These bands are used to describe the location of genes on each chromosome.

What is chromosome 4?

Humans normally have 46 chromosomes in each cell, divided into 23 pairs. Two copies of chromosome 4, one copy inherited from each parent, form one of the pairs. Chromosome 4 spans about 191 million DNA building blocks (base pairs) and represents more than 6 percent of the total DNA in cells.

Identifying genes on each chromosome is an active area of genetic research. Because researchers use different approaches to predict the number of genes on each chromosome, the estimated number of genes varies. Chromosome 4 likely contains 1,000 to 1,100 genes that provide instructions for making proteins. These proteins perform a variety of different roles in the body.
Genes on chromosome 4 are among the estimated 20,000 to 25,000 total genes in the human genome.

How are changes in chromosome 4 related to health conditions?

Many genetic conditions are related to changes in particular genes on chromosome 4. This list of disorders associated with genes on chromosome 4 provides links to additional information.
Changes in the structure or number of copies of a chromosome can also cause problems with health and development. The following chromosomal conditions are associated with such changes in chromosome 4.

cancers

Changes in chromosome 4 have been identified in several types of human cancer. These genetic changes are somatic, which means they are acquired during a person's lifetime and are present only in certain cells. For example, rearrangements (translocations) of genetic material between chromosome 4 and several other chromosomes have been associated with leukemias, which are cancers of blood-forming cells.
A specific translocation involving chromosome 4 and chromosome 14 is commonly found in multiple myeloma, which is a cancer that starts in cells of the bone marrow. The translocation, which is written as t(4;14)(p16;q32), abnormally fuses the WHSC1 gene on chromosome 4 with part of another gene on chromosome 14. The fusion of these genes overactivates WHSC1, which appears to promote the uncontrolled growth and division of cancer cells.

facioscapulohumeral muscular dystrophy

Facioscapulohumeral muscular dystrophy results from a deletion of genetic material from a region of DNA known as D4Z4. This region is located near the end of the long (q) arm of chromosome 4 at a position described as 4q35. The D4Z4 region normally consists of 11 to more than 100 repeated DNA segments, each of which is about 3,300 DNA base pairs (3.3 kb) long. However, in people with facioscapulohumeral muscular dystrophy the D4Z4 region on one copy of chromosome 4 is abnormally short, containing between 1 and 10 repeats.
It is uncertain how a shortened D4Z4 region causes the progressive muscle weakness and wasting characteristic of facioscapulohumeral muscular dystrophy. Researchers have proposed several possible mechanisms, but none have yet been proven. It appears that the D4Z4 region influences the activity of other genes located nearby on the long arm of chromosome 4. An abnormally short D4Z4 region may somehow disrupt the normal regulation of these genes. However, it is unclear which genes are influenced by D4Z4 and what role, if any, those genes play in muscle cells. Researchers suspect that genetic factors other than the shortened D4Z4 region may also be involved in facioscapulohumeral muscular dystrophy.

PDGFRA-associated chronic eosinophilic leukemia

PDGFRA-associated chronic eosinophilic leukemia is caused by genetic abnormalities that involve the PDGFRA gene, a gene found on chromosome 4. This condition is a type of blood cell cancer characterized by an increased number of eosinophils, a type of white blood cell involved in allergic reactions.
The PDGFRA gene abnormalities are somatic mutations, which are mutations acquired during a person's lifetime that are present only in certain cells. The most common of these abnormalities is a deletion of genetic material from chromosome 4 that removes approximately 800 DNA building blocks (nucleotides) and brings together parts of two genes, FIP1L1 and PDGFRA, creating the FIP1L1-PDGFRA fusion gene. Occasionally, through mechanisms other than deletion, genes other than FIP1L1 are fused with the PDGFRA gene. Rarely, mutations that change single DNA building blocks in the PDGFRA gene (point mutations) cause this condition.
The protein produced from the FIP1L1-PDGFRA fusion gene (as well as other PDGFRA fusion genes) has the function of the PDGFRA protein, which stimulates signaling pathways inside the cell that control many important cellular processes, such as cell growth and division (proliferation) and cell survival. Unlike the normal PDGFRA protein, however, the fusion protein is constantly turned on (constitutively activated), which means the cells are always receiving signals to proliferate. Similarly, point mutations in the PDGFRA gene can result in a constitutively activated PDGFRA protein. When the FIP1L1-PDGFRA fusion gene or point mutations in the PDGFRA gene occur in blood cell precursors, the growth of eosinophils (and occasionally other blood cells) is poorly controlled, leading to PDGFRA-associated chronic eosinophilic leukemia. It is unclear why eosinophils are preferentially affected by this genetic change.

Wolf-Hirschhorn syndrome

Wolf-Hirschhorn syndrome is caused by a deletion of genetic material near the end of the short (p) arm of chromosome 4 at a position described as 4p16.3. The signs and symptoms of this condition are related to the loss of multiple genes from this part of the chromosome. The size of the deletion varies among affected individuals; studies suggest that larger deletions tend to result in more severe intellectual disability and physical abnormalities than smaller deletions.
The region of chromosome 4 that is deleted most often in people with Wolf-Hirschhorn syndrome is known as Wolf-Hirschhorn syndrome critical region 2 (WHSCR-2). This region contains several genes, some of which are known to play important roles in early development. A loss of these genes leads to developmental delay, a distinctive facial appearance, and other characteristic features of the condition. Scientists are working to identify additional genes at the end of the short arm of chromosome 4 that contribute to the characteristic features of Wolf-Hirschhorn syndrome.

other chromosomal conditions

Some deletions of genetic material from the short (p) arm of chromosome 4 do not involve the critical region WHSCR-2. These deletions cause signs and symptoms that are distinct from those of Wolf-Hirschhorn syndrome, including mild intellectual disability and, in some cases, rapid (accelerated) growth. People with this type of deletion usually do not have seizures.
Trisomy 4 occurs when cells have three copies of chromosome 4 instead of the usual two copies. Full trisomy 4, which occurs when all of the body's cells contain an extra copy of chromosome 4, is not compatible with life. A similar but somewhat less severe condition called mosaic trisomy 4 occurs when only some of the body's cells have an extra copy of chromosome 4. The signs and symptoms of mosaic trisomy 4 vary widely and can include heart defects, abnormalities of the fingers and toes, and other birth defects. Mosaic trisomy 4 is very rare; only a few cases have been reported.
Other changes in the number or structure of chromosome 4 can have a variety of effects including delayed growth and development, intellectual disability, distinctive facial features, heart defects, and other medical problems. Changes involving chromosome 4 include an extra piece of the chromosome in each cell (partial trisomy 4), a missing segment of the chromosome in each cell (partial monosomy 4), and a circular structure called a ring chromosome 4. Ring chromosomes occur when a chromosome breaks in two places and the ends of the chromosome arms fuse together to form a circular structure.

Is there a standard way to diagram chromosome 4?

Geneticists use diagrams called ideograms as a standard representation for chromosomes. Ideograms show a chromosome's relative size and its banding pattern. A banding pattern is the characteristic pattern of dark and light bands that appears when a chromosome is stained with a chemical solution and then viewed under a microscope. These bands are used to describe the location of genes on each chromosome.

What is chromosome 3?

Humans normally have 46 chromosomes in each cell, divided into 23 pairs. Two copies of chromosome 3, one copy inherited from each parent, form one of the pairs. Chromosome 3 spans about 198 million base pairs (the building blocks of DNA) and represents approximately 6.5 percent of the total DNA in cells.
Identifying genes on each chromosome is an active area of genetic research. Because researchers use different approaches to predict the number of genes on each chromosome, the estimated number of genes varies. Chromosome 3 likely contains 1,000 to 1,100 genes that provide instructions for making proteins. These proteins perform a variety of different roles in the body.
Genes on chromosome 3 are among the estimated 20,000 to 25,000 total genes in the human genome.

How are changes in chromosome 3 related to health conditions?

Many genetic conditions are related to changes in particular genes on chromosome 3. This list of disorders associated with genes on chromosome 3 provides links to additional information.

Is there a standard way to diagram chromosome 3?

Geneticists use diagrams called ideograms as a standard representation for chromosomes. Ideograms show a chromosome's relative size and its banding pattern. A banding pattern is the characteristic pattern of dark and light bands that appears when a chromosome is stained with a chemical solution and then viewed under a microscope. These bands are used to describe the location of genes on each chromosome.

What is chromosome 2?

Humans normally have 46 chromosomes in each cell, divided into 23 pairs. Two copies of chromosome 2, one copy inherited from each parent, form one of the pairs. Chromosome 2 is the second largest human chromosome, spanning about 243 million building blocks of DNA (base pairs) and representing almost 8 percent of the total DNA in cells. Identifying genes on each chromosome is an active area of genetic research. Because researchers use different approaches to predict the number of genes on each chromosome, the estimated number of genes varies. Chromosome 2 likely contains 1,300 to 1,400 genes that provide instructions for making proteins. These proteins perform a variety of different roles in the body.
Genes on chromosome 2 are among the estimated 20,000 to 25,000 total genes in the human genome.

How are changes in chromosome 2 related to health conditions?

Many genetic conditions are related to changes in particular genes on chromosome 2. This list of disorders associated with genes on chromosome 2 provides links to additional information.
Changes in the structure or number of copies of a chromosome can also cause problems with health and development. The following chromosomal conditions are associated with such changes in chromosome 2.

cancers

Changes in chromosome 2 have been identified in several types of cancer. These genetic changes are somatic, which means they are acquired during a person's lifetime and are present only in certain cells. For example, a rearrangement (translocation) of genetic material between chromosomes 2 and 3 has been associated with cancers of a certain type of blood cell originating in the bone marrow (myeloid malignancies).
Trisomy 2, in which cells have three copies of chromosome 2 instead of the usual two copies, has been found in myelodysplastic syndrome. This disease affects the blood and bone marrow. People with myelodysplastic syndrome have a low number of red blood cells (anemia) and an increased risk of developing a form of blood cancer known as acute myeloid leukemia.

2q37 deletion syndrome

2q37 deletion syndrome is caused by a deletion of genetic material from a specific region in the long (q) arm of chromosome 2. The deletion occurs near the end of the chromosome at a location designated 2q37. The size of the deletion varies among affected individuals. The signs and symptoms of this disorder, which may include intellectual disability, autism, short stature, obesity, and characteristic facial features, are probably related to the loss of multiple genes in this region.

other chromosomal conditions

Another chromosome 2 abnormality is known as a ring chromosome 2. A ring chromosome is formed when breaks occur at both ends of the chromosome and the broken ends join together to form a circular structure. Individuals with this chromosome abnormality often have developmental delay, small head size (microcephaly), slow growth before and after birth, heart defects, and distinctive facial features. The severity of symptoms typically depends on how many and which types of cells contain the ring chromosome 2.
Other changes involving the number or structure of chromosome 2 include an extra piece of the chromosome in each cell (partial trisomy 2) or a missing segment of the chromosome in each cell (partial monosomy 2). These changes can have a variety of effects on health and development, including intellectual disability, slow growth, characteristic facial features, weak muscle tone (hypotonia), and abnormalities of the fingers and toes.

Is there a standard way to diagram chromosome 2?

Geneticists use diagrams called ideograms as a standard representation for chromosomes. Ideograms show a chromosome's relative size and its banding pattern. A banding pattern is the characteristic pattern of dark and light bands that appears when a chromosome is stained with a chemical solution and then viewed under a microscope. These bands are used to describe the location of genes on each chromosome.

What is chromosome 1?

Humans normally have 46 chromosomes in each cell, divided into 23 pairs. Two copies of chromosome 1, one copy inherited from each parent, form one of the pairs. Chromosome 1 is the largest human chromosome, spanning about 249 million DNA building blocks (base pairs) and representing approximately 8 percent of the total DNA in cells.
Identifying genes on each chromosome is an active area of genetic research. Because researchers use different approaches to predict the number of genes on each chromosome, the estimated number of genes varies. Chromosome 1 likely contains 2,000 to 2,100 genes that provide instructions for making proteins. These proteins perform a variety of different roles in the body.
Genes on chromosome 1 are among the estimated 20,000 to 25,000 total genes in the human genome.

How are changes in chromosome 1 related to health conditions?

Many genetic conditions are related to changes in particular genes on chromosome 1. This list of disorders associated with genes on chromosome 1 provides links to additional information.
Changes in the structure or number of copies of a chromosome can also cause problems with health and development. The following chromosomal conditions are associated with such changes in chromosome 1.

1p36 deletion syndrome

1p36 deletion syndrome is caused by a deletion of genetic material from a specific region in the short (p) arm of chromosome 1. The signs and symptoms of this disorder, which include intellectual disability, distinctive facial features, and structural abnormalities in several body systems, are probably related to the loss of multiple genes in this region. The size of the deletion varies among affected individuals.

1q21.1 microdeletion

1q21.1 microdeletion is a chromosomal change in which a small piece of the long (q) arm of chromosome 1 is deleted in each cell. Specifically, affected individuals are missing about 1.35 million DNA building blocks (base pairs), also written as 1.35 megabases (Mb), in the q21.1 region. The exact size of the deleted region varies, but it typically contains at least nine genes. The loss of several of these genes probably contributes to the various signs and symptoms that can be associated with a 1q21.1 microdeletion. Related features can include delayed development, intellectual disability, physical abnormalities, and neurological and psychiatric problems; however, some individuals with a 1q21.1 microdeletion have no obvious signs or symptoms.

neuroblastoma

Deletions within region 1p36 have also been associated with another condition called neuroblastoma. Neuroblastoma is a type of cancerous tumor composed of immature nerve cells (neuroblasts). These deletions are somatic mutations, which means they occur during a person's lifetime and are present only in the cells that become cancerous. About 25 percent of people with neuroblastoma have a deletion of 1p36.1-1p36.3, which is associated with a more severe form of neuroblastoma. Researchers believe the deleted region could contain a gene that keeps cells from growing and dividing too quickly or in an uncontrolled way, called a tumor suppressor gene. When tumor suppressor genes are deleted, cancer can occur. Researchers have identified several possible tumor suppressor genes in the deleted region of chromosome 1, and more research is needed to understand what role these genes play in neuroblastoma development.

thrombocytopenia-absent radius syndrome

A deletion in the 1q21.1 region of chromosome 1 is involved in most cases of thrombocytopenia-absent radius (TAR) syndrome. TAR syndrome is characterized by the absence of a bone called the radius in each forearm and a shortage (deficiency) of blood cells involved in clotting (platelets).
The deletion in chromosome 1 involved in TAR syndrome eliminates at least 200,000 DNA building blocks (200 kilobases, or 200 kb) from the long (q) arm of the chromosome, including a gene called RBM8A. Most people with TAR syndrome have the deletion in one copy of chromosome 1, which removes one copy of the RBM8A gene, and a mutation in the other copy of the RBM8A gene in each cell. The RBM8A gene provides instructions for making a protein called RNA-binding motif protein 8A. This protein is believed to be involved in a number of important cellular functions involving the production of other proteins.
RBM8A gene mutations that cause TAR syndrome reduce the amount of RNA-binding motif protein 8A in cells. The deletion on chromosome 1 eliminates one copy of the RBM8A gene in each cell and the RNA-binding motif protein 8A that would have been produced from it. The reduced total amount of RNA-binding motif protein 8A is thought to cause problems in the development of certain tissues, but it is unknown how it causes the specific signs and symptoms of TAR syndrome. No cases have been reported in which individuals have deletions on both copies of chromosome 1 that include both copies of the RBM8A gene; studies indicate that the complete loss of RNA-binding motif protein 8A is not compatible with life.
Researchers sometimes refer to the deletion in chromosome 1 associated with TAR syndrome as the 200-kb deletion to distinguish it from another chromosomal abnormality called a 1q21.1 microdeletion. People with a 1q21.1 microdeletion are missing a different, larger DNA segment in the chromosome 1q21.1 region near the area where the 200-kb deletion occurs. The chromosomal change related to 1q21.1 microdeletion is often called the recurrent distal 1.35-Mb deletion.

other cancers

Changes in the structure of chromosome 1 are associated with other forms of cancer and conditions related to cancer. These changes are typically somatic, which means they are acquired during a person's lifetime and are present only in tumor cells.
Deletions in the short (p) arm of the chromosome have been identified in tumors of the brain and kidney. Duplications in the long (q) arm of the chromosome have been reported in a disorder called myelodysplastic syndrome, which is a disease of the blood and bone marrow. People with this condition have a low number of red blood cells (anemia) and an increased risk of developing leukemia.

other chromosomal conditions

Other changes in the number or structure of chromosome 1 can have a variety of effects, including delayed growth and development, distinctive facial features, birth defects, and other health problems. Changes to chromosome 1 may include an extra segment of the short (p) or long (q) arm of the chromosome in each cell (partial trisomy 1p or 1q), a missing segment of the short or long arm of the chromosome in each cell (partial monosomy 1p or 1q), or a circular structure called ring chromosome 1. Ring chromosomes occur when a chromosome breaks in two places and the ends of the chromosome arms fuse together to form a circular structure.

Is there a standard way to diagram chromosome 1?

Geneticists use diagrams called ideograms as a standard representation for chromosomes. Ideograms show a chromosome's relative size and its banding pattern. A banding pattern is the characteristic pattern of dark and light bands that appears when a chromosome is stained with a chemical solution and then viewed under a microscope. These bands are used to describe the location of genes on each chromosome.

What is the Y chromosome?

The Y chromosome is one of the two sex chromosomes in humans (the other is the X chromosome). The sex chromosomes form one of the 23 pairs of human chromosomes in each cell. The Y chromosome spans more than 59 million building blocks of DNA (base pairs) and represents almost 2 percent of the total DNA in cells.
Each person normally has one pair of sex chromosomes in each cell. The Y chromosome is present in males, who have one X and one Y chromosome, while females have two X chromosomes.
Identifying genes on each chromosome is an active area of genetic research. Because researchers use different approaches to predict the number of genes on each chromosome, the estimated number of genes varies. The Y chromosome likely contains 50 to 60 genes that provide instructions for making proteins. Because only males have the Y chromosome, the genes on this chromosome tend to be involved in male sex determination and development. Sex is determined by the SRY gene, which is responsible for the development of a fetus into a male. Other genes on the Y chromosome are important for male fertility.
Many genes are unique to the Y chromosome, but genes in areas known as pseudoautosomal regions are present on both sex chromosomes. As a result, men and women each have two functional copies of these genes. Many genes in the pseudoautosomal regions are essential for normal development.
Genes on the Y chromosome are among the estimated 20,000 to 25,000 total genes in the human genome.

How are changes in the Y chromosome related to health conditions?

Many genetic conditions are related to changes in particular genes on the Y chromosome. This list of disorders associated with genes on the Y chromosome provides links to additional information.
Changes in the structure or number of copies of a chromosome can also cause problems with health and development. The following chromosomal conditions are associated with such changes in the Y chromosome.

46,XX testicular disorder of sex development

In most individuals with 46,XX testicular disorder of sex development, the condition results from an abnormal exchange of genetic material between chromosomes (translocation). This exchange occurs as a random event during the formation of sperm cells in the affected person's father. The translocation affects the gene responsible for development of a fetus into a male (the SRY gene). The SRY gene, which is normally found on the Y chromosome, is misplaced in this disorder, almost always onto an X chromosome. A fetus with an X chromosome that carries the SRY gene will develop as a male despite not having a Y chromosome.

48,XXYY syndrome

48,XXYY syndrome is caused by the presence of an extra X chromosome and an extra Y chromosome in a male's cells. Extra genetic material from the X chromosome interferes with male sexual development, preventing the testes from functioning normally and reducing the levels of testosterone (a hormone that directs male sexual development) in adolescent and adult males. Extra copies of genes from the pseudoautosomal region of the extra X and Y chromosome contribute to the signs and symptoms of 48,XXYY syndrome; however, the specific genes have not been identified.

47,XYY syndrome

Males with 47,XYY syndrome have one X chromosome and two Y chromosomes in each cell, for a total of 47 chromosomes. It is unclear why an extra copy of the Y chromosome is associated with tall stature, learning problems, and other features in some boys and men.
Some males with 47,XYY syndrome have an extra Y chromosome in only some of their cells. This phenomenon is called 46,XY/47,XYY mosaicism.

Y chromosome infertility

Y chromosome infertility is usually caused by deletions of genetic material in regions of the Y chromosome called azoospermia factor (AZF) A, B, or C. Genes in these regions are believed to provide instructions for making proteins involved in sperm cell development, although the specific functions of these proteins are unknown.
Deletions in the AZF regions may affect several genes. The missing genetic material likely prevents production of a number of proteins needed for normal sperm cell development, resulting in an inability to father children.

other chromosomal conditions

Chromosomal conditions involving the sex chromosomes often affect sex determination (whether a person has the sexual characteristics of a male or a female), sexual development, and the ability to have children (fertility). The signs and symptoms of these conditions vary widely and range from mild to severe. They can be caused by missing or extra copies of the sex chromosomes or by structural changes in these chromosomes.
Rarely, males may have more than one extra copy of the Y chromosome in every cell (polysomy Y). For example, the presence of two extra Y chromosomes is written as 48,XYYY. The extra genetic material in these cases can lead to skeletal abnormalities, decreased IQ, and delayed development, but the features of these conditions are variable.

Is there a standard way to diagram the Y chromosome?

Geneticists use diagrams called ideograms as a standard representation for chromosomes. Ideograms show a chromosome's relative size and its banding pattern. A banding pattern is the characteristic pattern of dark and light bands that appears when a chromosome is stained with a chemical solution and then viewed under a microscope. These bands are used to describe the location of genes on each chromosome.