Chromosome Sentence Examples

As they pass into this position they undergo a longitudinal splitting by which the chromatin in each chromosome becomes divided into equal halves.

I also have a report by Dr. Tartaglia on girls with a chromosome anomaly.

The sperm carries either another X or a Y chromosome.

A typical breast cancer, for example, will have 10 to 20 chromosome aberrations.

By studying the reading and writing abilities of close to 80 family members across four generations, the researchers reported, for the first time, that chromosome 2 can be involved in the inheritability of dyslexia.

Partial trisomy of the proximal segment of chromosome 13 is much less likely to be fatal and has been associated with a variety of facial features including a large nose, a short upper lip, and a receding jaw.

There is also a type of ocular albinism that is carried on the X chromosome and occurs almost exclusively in males because they have only one X chromosome and, therefore, no other gene for the trait to override the defective one.

Female children, on the other hand, have two copies of the X chromosome, which often leaves them one normal X chromosome to fall back on to produce that essential protein, allowing proper development to occur.

Each chromosome is really a very long DNA molecule.

However, it is estimated that 3 to 8 percent of girls with a single X chromosome and 12 to 21 percent of females with sex chromosome mosaicism may have normal pubertal development and spontaneous menstrual periods.

If there is a green allele on chromosome 19 and the rest of the allele on chromosome 19 and the rest of the alleles are blue, eye color will be green.

Three major histocompatibility antigens are encoded on each copy of chromosome 6, but they are inherited as a group.

Press Release | Sequence Data | Nature Article | Author List About Chromosome 22 Chromosome 22 is the second smallest of the human autosomes.

They each consist of two threads called chromatids, each an exact copy of the parent chromosome.

Each chromosome has divided to produce 2 identical chromatids, joined at a structure called the centromere.

Each chromosome is really a very long molecule of DNA wound up and coiled around special proteins to form chromatin.

The whole region has been physically mapped to porcine chromosome 6 using in situ hybridisation.

The Plasmodium falciparum chromosome 2 project was funded by the National Institute of Allergy and Infectious Diseases (NIAID ).

With this strategy variations between metaphases due to different chromosome condensation can be minimized.

We attempted to characterize these chromosome 13q deletions at the molecular cytogenetic level.

The allelic deletions on chromosome arms 15q and 16q have not been defined previously for SCLC and are candidate regions to harbor novel TSGs.

This approach permitted the simultaneous evaluation of ploidy changes and chromosome arm deletions.

A mutation in a receptor for the neurotransmitter dopamine has been found on chromosome 11 or 18.

The genes coding for the alpha globins are on chromosome 11; those coding for the beta globins are on chromosome 16.

Blood Chromosome Analysis This is performed on a 5-10ml fresh, sterile sample of venous blood in a lithium heparin container.

This allows the simultaneous analysis of every chromosome for submicroscopic chromosome imbalances using only a single slide per patient.

Human Genome Project; Human chromosome launchpad The Human Chromosome Launchpad provides links to research resources for each human chromosome.

Josh Eaton's Home Page A 7 year old who has had a bone marrow transplant for Philadelphia chromosome positive acute lymphoblastic leukemia.

The MBL2 gene on chromosome 10 is the blueprint for a protein called mannose binding protein that is similar in shape to C1q.

Therefore mutation provides a mechanism for adding random genetic material into the chromosome by changing one or more of the gene values at random.

To study meiosis, it is necessary to investigate the consequences to chromosome segregation of altering particular proteins.

Our studies also suggest the existence of another processed pseudogene on chromosome 11.

David Perkins gave an overview of the study of fungal chromosome rearrangements.

They also provide a binding point outside of the main chromosome where replication of the chromosome ends can occur from.

The production of gametes, be they sperm in males or eggs in females, requires major changes in the mechanism of chromosome segregation.

Analysis of the " X " chromosome - the female sex chromosome - has revealed that women are genetically more complicated than men.

Almost a third of adult patients have a specific chromosome translocation; " Philadelphia Positive " ALL.

Parental chromosome analysis should be offered where trisomy 13 is due to an unbalanced translocation.

The bollworm was modified using the piggyBac transposon that inserts at the sequence, TTAA in the chromosome (see above ).

Vega database for dog contains 700 kbp of the MHC region on chromosome 12 comprising fully annotated clones only.

Visible differences in the chromosomes have even been observed, especially in insects, which are due apparently to an unequal division by which an additional or accessory chromosome is produced, or in some cases one or two extra chromosomes which differ in size from the others.

From numerous investigations which have been made to trace the chromosomes through the various stages of the nuclear ontogeny of plant cells, it appears that the individuality and continuity of the chromosomes can only be conceived as possible if we assume the existence of something like chromosome centres in the resting nucleus around which the chromosomes become organized fon purposes of division.

The male-specific region of the human Y chromosome is a mosaic of discrete sequence classes.

The DNA sequence of the human Y chromosome - the ' maleness ' chromosome - has been published.

Parents were almost always not prepared for the possibility of a sex chromosome anomaly and reacted with confusion.

Future directions Several challenges now face those researching spermatogenesis genes on the Y chromosome.

A genome-wide scan for human obesity genes reveals a major susceptibility locus on chromosome 10.

The bollworm was modified using the piggyBac transposon that inserts at the sequence, TTAA in the chromosome (see above).

The other fuses with genetic material in the ovule to produce a triploid tissue (has three copies of each chromosome).

Dog The vega database for dog contains 700 kbp of the MHC region on chromosome 12 comprising fully annotated clones only.

The color gene is also tied into the sex chromosome.

The only true male calicos will typically have an extra X chromosome.

The most common type of CMT, called CMT1A, is caused by a mutation in a gene called peripheral myelin protein 22 (PMP22) located on chromosome 17.

Instead of having two copies of the PMP22 gene (one on each chromosome) there are three copies.

Another type of CMT, called CMT1B, is caused by a mutation in a gene called myelin protein zero (MPZ), located on chromosome 1.

In CMTX, the CMT-causing gene is located on the X chromosome and is called connexin 32 (Cx32).

Since males only have one X chromosome, they only have one copy of the Cx32 gene.

If a woman with a Cx32 mutation passes her normal X chromosome, she will have an unaffected son or daughter who will not pass CMT on to his or her children.

If the woman passes the chromosome with Cx32 mutation on she will have an affected son or daughter, although the daughter will be mildly affected or have no symptoms.

When males pass on an X chromosome, they have a daughter.

When they pass on a Y chromosome, they have a son.

Since the Cx32 mutation is on the X chromosome, a man with CMTX will always pass the Cx32 mutation on to his daughters.

However, when he has a son, he passes on the Y chromosome, and the son will not be affected.

Trisomy-An abnormal condition where three copies of one chromosome are present in the cells of an individual's body instead of two, the normal number.

A female child inherits two X chromosomes, while a male child inherits an X chromosome from one parent and a Y chromosome from the other.

If a defective gene encoding for a disease is found on the X chromosome, then a male child cannot have a healthy copy of the gene (since he only has one X chromosome); therefore, he will develop the disorder.

Female children are at less risk because they have to have two copies of the defective gene (one on each X chromosome) in order to develop the disease.

This form of EDS is caused by a change in the PLOD gene on chromosome 1, which encodes the enzyme lysyl hydroxylase.

Because chromosomes are inherited in pairs, each individual receives two copies of each chromosome and likewise two copies of each gene.

In X-linked EDS, a specific gene on the X chromosome must be changed.

If a father with an X-linked recessive form of EDS passes a copy of his X chromosome to his children, the sons will be unaffected and the daughters will be carriers.

If a mother is a carrier for an X-linked recessive form of EDS, she may have affected or unaffected sons, or carrier or unaffected daughters, depending on the second sex chromosome inherited from the father.

The rate of mutation of the fibrillin gene, however, appears to be related to the age of the child's father; older fathers are more likely to have new mutations appear in chromosome 15.

Marfan syndrome is caused by a single gene for fibrillin on chromosome 15, which is inherited in most cases from an affected parent.

Also, older fathers are more likely to have new mutations appear in chromosome 15.

An autosomal disorder is one that occurs because of an abnormal gene on a chromosome that is not a sex-linked chromosome.

Each gene is found on a precise location on a chromosome.

Fragile X, a defect in the chromosome that determines sex, is the most common inherited cause of mental retardation.

Examples of such accidents are development of an extra chromosome 18 (trisomy 18) and Down syndrome.

Down syndrome is caused by an abnormality in the development of chromosome 21.

Down syndrome-A chromosomal disorder caused by an extra copy or a rearrangement of chromosome 21.

Turner syndrome-A chromosome abnormality characterized by short stature and ovarian failure caused by an absent X chromosome.

This condition has an X-linked, recessive pattern of inheritance, meaning that the defective gene is carried on the X chromosome.

A female who carries a defective recessive gene on one of her two X chromosomes will not have the disease because she also has one good X chromosome.

The sons inheriting one defective gene will develop the disorder because a male has only one X chromosome, which he receives from his mother and one Y chromosome from his father.

The amniotic fluid can be examined for signs of chromosome abnormalities or other genetic diseases.

X-linked-A gene carried on the X chromosome, one of the two sex chromosomes.

Blood tests can check the levels of sex hormones in the baby's blood, and chromosome analysis (called karyotyping) can determine sex.

In FA, the frataxin gene on chromosome 9 is expanded when a particular sequence of bases in the DNA is repeated too many times.

The ATM gene is located on the long arm of chromosome 11 at position 11q22-23.

Increased chromosome breaks and rearrangements.

Mutations in the MEFV gene (short for Mediterranean fever) on chromosome number 16 are the underlying cause of FMF.

Genetic counseling and further testing, such as chromosome analysis before pregnancy, or amniocentesis during pregnancy, may be recommended in adults with atrial septal defects.

Researchers believe the defect responsible for Marfan's syndrome is found in gene FBN1 on chromosome 15.

Genetic counseling and further testing, such as chromosome analysis before pregnancy or amniocentesis during pregnancy, may be recommended in adults with congenital cardiovascular defects.

Wilson's disease, which is caused by a mutation of the ATP7B gene on chromosome 13, first produces symptoms in teenagers and young adults.

Menkes disease-A genetic disease caused by a mutation on the X chromosome and resulting in impaired transport of copper from the digestive tract.

Unlike the other MPS conditions, MPS II is inherited in an X-linked recessive manner, which means that the gene causing the condition is located on the X chromosome, one of the two sex chromosomes.

A male child inherits an X chromosome from his mother and a Y chromosome from his father.

He will have the disorder if the X chromosome inherited from his mother carries the defective gene, since he has only one (nonfunctioning) copy of the gene.

Females inherit one X chromosome from their mother and a second X chromosome from their father.

Because they have two X chromosomes, they are carriers of the disorder if one of their X chromosomes has the gene that causes the condition, while the other X chromosome does not.

All individuals with Hunter syndrome are male, because the gene that causes the condition is located on their single X chromosome.

The gene that causes MPS IIIA is located on the long arm of chromosome 17.

The gene associated with MPS IIIB is also located on the long arm of chromosome 17.

The gene involved in MPS IIIC is believed to be located on chromosome 14.

The gene involved in MPS IIID is located on the long arm of chromosome 12.

The gene involved with MPS IV A is located on the long arm of chromosome 16.

The gene that produces beta-galactosidase is located on the short arm of chromosome 3.

The gene involved in MPS VI is believed to be located on the long arm of chromosome 5.

The gene that causes MPS VII is located on the long arm of chromosome 7.

The gene involved in MPS IX is believed to be located on the short arm of chromosome 3.

X-linked gene-A gene carried on the X chromosome, one of the two sex chromosomes.

Spina bifida may arise because of chromosome abnormalities, single gene mutations, or specific environmental insults such as maternal diabetes mellitus or prenatal exposure to certain anticonvulsant drugs.

Tuberous sclerosis occurs when at least one of two genes (either TSC-1 on chromosome 9 or TSC-2 on chromosome 16) is defective.

Being located at 9q34 means that it is on the long arm (q) of chromosome 9 in the 34 region.

These cells are then tested for chromosome abnormalities or other genetic diseases.

In 1999 researchers identified the gene that causes narcolepsy on chromosome 12.

Fragile X syndrome, in which a segment of the chromosome that determines gender is abnormal, primarily affects males.

Fragile X syndrome-A genetic condition related to the X chromosome that affects mental, physical, and sensory development.

Autosome-A chromosome not involved in sex determination.

The somatic cells contain two of each chromosome 13 and, therefore, two copies of the RB1 gene.

Each egg and sperm cell contains only one copy of chromosome and, therefore, only one copy of the RB1 gene.

Chromosome testing would be recommended for the blood relatives of the parent with the abnormality.

If chromosome or DNA testing identifies an RB1 gene/deletion in someone's blood cells, then prenatal testing can be performed on this person's offspring.

Fragile X syndrome, a genetic condition involving changes in the long arm of the X chromosome, is the most common form of inherited mental retardation.

Generally, males are affected with moderate mental retardation (since they only have one X chromosome) and females with mild mental retardation.

Fragile X syndrome is caused by a mutation in the FMR-1 gene, located on the X chromosome.

When a man carries a premutation on his X chromosome, it tends to be stable and usually will not expand if he passes it on to his daughters (he passes his Y chromosome to his sons).

Since the FMR-1 gene is located on the X chromosome, males are more likely to develop symptoms than females.

This greater inclination occurs because males have only one copy of the X chromosome.

A female's normal X chromosome may compensate for her chromosome with the fragile X gene mutation.

The chorionic membrane can be examined for signs of chromosome abnormalities or other genetic diseases.

Normal males have both an X and a Y chromosome, and normal females have two X chromosomes.

Most individuals have four normal copies of the alpha globin gene, two copies on each chromosome 16.

This syndrome can be caused by a deletion of a significant amount of chromosome 16, affecting the alpha globin genes.

Most individuals have two normal copies of the beta globin gene, which is located on chromosome 11 and makes the beta globin component of normal adult hemoglobin.

Patau syndrome, also called trisomy 13, is a congenital (present at birth) disorder associated with the presence of an extra copy of chromosome 13.

The extra chromosome 13 causes numerous physical and mental abnormalities, especially heart defects.

A condition called trisomy occurs when three, instead of two, copies of a chromosome are present in a developing human embryo.

An extra copy of a particular chromosome can come either from the egg or sperm or from mutations that occur after conception.

The most well-known trisomy-related disorder is Down syndrome (trisomy 21), in which the developing embryo has an extra copy of chromosome 21.

Patau syndrome is trisomy 13, in which the developing embryo has three copies of chromosome 13.

An extra copy of chromosome 13 is not the only cause of Patau syndrome.

Other changes in chromosome 13, such as mispositioning (translocation), can also result in the characteristics classified as Patau syndrome.

In these cases, an error occurs that causes a portion of chromosome 13 to be exchanged for a portion of another chromosome.

There is no production of extra chromosomes, but a portion of each affected chromosome is "misplaced" (translocated) to another chromosome.

Patau syndrome is confirmed by the presence of three, rather than the normal two, copies of the thirteenth largest chromosome.

Karyotyping-A laboratory test used to study an individual's chromosome make-up.

A balanced translocation occurs when pieces from two different chromosomes exchange places without loss or gain of any chromosome material.

Mild and severe hemophilia A are inherited through a complex genetic system that passes a recessive gene on the female chromosome.

An abnormal chromosome known as the Philadelphia chromosome is seen in 90 percent of those with CML.

The DMPK gene is located on chromosome 19.

Instead, they have a mutation in a gene on chromosome 3 that causes four units within the gene to be repeated.

It is caused by mutations in a gene known as LIM Homeobox Transcription Factor 1-Beta (LMX1B), located on the long arm of chromosome 9.

The more common of the two, known as X-linked hyper-IgM syndrome (XHIM), is caused by an abnormal gene on the X chromosome and affects only boys.

Hyper-IgM syndrome is caused by a mutation in a gene on the X chromosome that affects the patient's T cells.

Turner syndrome is a birth defect caused by the absence of an X chromosome in some or all cells of a female, which inhibits sexual development and usually causes infertility.

Normally, females have two X chromosomes, and males have one X and one Y chromosome.

The missing chromosome is an X chromosome.

About 1 to 2 percent of all female conceptions have a missing X chromosome.

This specific learning problem is referred to as Turner neurocognitive phenotype and appears to be due to loss of X chromosome genes important for selected aspects of nervous system development.

The genetic region responsible for it has been localized on its chromosome, however.

While the X chromosome carries many genes, the Y chromosome carries almost none.

Therefore, a male has only one copy of each gene on the X chromosome, and if it is flawed, he will have the disease that defect causes.

He will pass the flawed gene on to each of his daughters, who will then be carriers, but to none of his sons (because they inherit his Y chromosome).

The PAH gene and its PKU mutations are found on chromosome 12 in the human genome.

The term autosomal means that the gene for PKU is not located on either the X or Y sex chromosome.

X-linked agammaglobulinemia is an inherited disease stemming from a defect on the X chromosome, consequently affecting more males than females.

Hemophilia is a coagulation disorder arising from a genetic defect of the X chromosome; the defect can either be inherited or result from spontaneous gene mutation.

Hemophilia A and B are both caused by a genetic defect present on the X chromosome.

Both factors VIII and IX are produced by a genetic defect of the X chromosome, so hemophilia A and B are both sex-linked diseases passed on from a female to male offspring.

Because the trait is carried only on the X chromosome, it is called sex-linked.

Because a female child always receives two X chromosomes, she will nearly always receive at least one normal X chromosome.

Therefore, even if she receives one flawed X chromosome, she will still be capable of producing a sufficient quantity of factors VIII and IX to avoid the symptoms of hemophilia.

Such a person who has one flawed chromosome but does not actually suffer from the disease is called a carrier.

If, however, she has a son who receives her flawed X chromosome, he will be unable to produce the right quantity of factors VIII or IX, and he will suffer some degree of hemophilia.

Once such a spontaneous genetic mutation takes place, offspring of the affected person can inherit the newly created, flawed chromosome.

Edwards' syndrome is caused by an extra (third) copy of chromosome 18.

The extra chromosome is lethal for most babies born with this condition.

Edwards' syndrome is associated with the presence of a third copy of chromosome number 18.

Using special stains and microscopy, individual chromosomes are identified, and the presence of an extra chromosome 18 is revealed.

Klinefelter syndrome is a chromosome disorder in males that results in hypogonadism (small penis and small firm testicles).

People with this condition are born with at least one extra X chromosome.

Females have two X chromosomes (the XX combination); males have one X and one Y chromosome (the XY combination).

The extra chromosome is an X chromosome.

Because people with Klinefelter syndrome have a Y chromosome, they are all male.

Approximately 1/3 of all males with Klinefelter syndrome have other chromosome changes involving an extra X chromosome.

Mosaic Klinefelter syndrome occurs when some of the cells in the body have an extra X chromosome and the other have normal male chromosomes.

Males with more than one additional extra X chromosome, such as 48, XXXY, are usually more severely affected than males with 47,XXY.

Diagnosis of Klinefelter syndrome is confirmed by examining chromosomes for evidence of more than one X chromosome present in a male.

If the diagnosis of Klinefelter syndrome is suspected in a young boy or adult male, chromosome testing can also be on a small blood or skin sample after birth.

Down syndrome is a condition that includes mental retardation and a distinctive physical appearance linked to an abnormality of chromosome 21 (called trisomy 21).

Genetic abnormalities such as craniosynostosis are described by the type of chromosome that carries the abnormal gene and whether the gene is recessive or dominant.

Cri du chat (a French phrase that means "cry of the cat") syndrome is a group of symptoms that result when a piece of chromosomal material is missing (deleted) from a particular region on chromosome 5.

Cri du chat syndrome is also called 5p minus syndrome or chromosome 5p deletion syndrome because it is caused by a deletion, or removal, of genetic material from chromosome 5.

The deletion that causes cri du chat syndrome occurs on the short or p arm of chromosome 5.

Cri du chat is the result of a chromosome abnormality-a deleted piece of chromosomal material on chromosome 5.

If a child has this unusual cry or other features seen in cri du chat syndrome, chromosome testing should be performed.

Chromosome analysis provides the definitive diagnosis of cri du chat syndrome and can be performed from a blood test.

Chromosome analysis, also called karyotyping, involves staining the chromosomes and examining them under a microscope.

In some cases the deletion of material from chromosome 5 can be easily seen.

This testing would only be recommended if the mother or father is known to have a chromosome rearrangement, or if they already have a child with cri du chat syndrome.

It is seen only in males because it is caused by a genetic defect on the X chromosome.

Since males have only one X chromosome, they always have the defect if the gene is present.

Females can have the defective gene, but since they have two X chromosomes, there will be a normal gene on the other X chromosome to counter it.

The most common form of SCID is X-linked, i.e. the defect is on the X chromosome and, therefore, occurs only in boys.

Karyotype-A standard arrangement of photographic or computer-generated images of chromosome pairs from a cell in ascending numerical order, from largest to smallest.

Although persons with XLA carry the genes to produce immunoglobulins, a genetic defect on the X chromosome prevents their formation.

The gene that controls the production of Btk is on the X chromosome.

Males have one X and one Y chromosome (XY).

The mother passes one of her two X chromosomes down to her child, and the father passes either an X or a Y chromosome to the child.

Boys only have one copy of the gene, because they only have one X chromosome.

To make a definitive diagnosis, the child's X chromosome is analyzed for defects in the Btk gene.

Some brain defects are caused by trisomy, the inclusion of a third copy of a chromosome normally occurring in pairs.

Trisomy of chromosome 9 can cause some cases of Dandy-Walker and Chiari II malformation.

Some cases of holoprosencephaly are caused by trisomy of chromosome 13, while others are due to abnormalities in chromosomes 7 or 18.

The complex genetics of VWD involve a gene found on chromosome 12.

Previous studies have pointed out linkages of other potential dyslexia genes to chromosome 1, chromosome 15 (DYX1 gene), and to chromosome 6 (DYX2 gene).

The researchers who pinpointed the localized gene on chromosome 2 (DYX3) hope that this finding will lead to earlier and more precise diagnoses of dyslexia.

Most cases of Angelman's syndrome can be traced to a genetic abnormality inherited from a maternal chromosome (15).

Careful chromosomal study can reveal abnormalities on chromosome 15 that are consistent with those identified in Angelman's syndrome.

Specialized testing of chromosome 15 will be required; the usual tests done during amniocentesis or chorionic villi sampling will not reveal the specific, small genetic flaw that causes Angelman syndrome.

An autosomal dominant trait is a gene that is not related to the chromosome that determines gender; therefore, it affects boys and girls equally.

In 2003, a team of Finnish researchers reported finding a candidate gene for developmental dyslexia on human chromosome 15q21.

Proof that genetic factors contribute to Hirschsprung's disease is that it is known to run in families, and it has been seen in association with some chromosome abnormalities.

For example, about 10 percent of children with the disease have Down syndrome (the most common chromosome abnormality).

Females have two X chromosomes, while males have one X and one Y chromosome.

Male sperm cells contain either an X or a Y; if the sperm with the Y chromosome fertilizes an egg, the baby will be male.

Males with this disorder have an extra Y chromosome.

The error that causes the extra Y chromosome can occur in the fertilizing sperm or in the developing embryo.

Turner's syndrome is a genetic disorder caused by a missing X chromosome that occurs only in females.

The 21-hydroxylase gene is made by a gene located on the short arm of chromosome 6.

This gene is located in an area of the chromosome that contains many other important genes whose products control immune function.

The gene responsible for WAS is located on the short arm of the X chromosome.

Since males have only one X chromosome they only have one copy of the gene.

They have a normal copy of the gene on one chromosome even if an abnormal gene is on the other because the abnormal gene is very rare.

The normal copy on one X chromosome is usually sufficient to prevent females from having WAS.

Researchers identified the gene for WAS in 1994 and pinpointed its location on the short arm of the X chromosome.

DiGeorge syndrome is a rare congenital disease that affects an infant's immune system and that is due to a large deletion from chromosome 22.

DiGeorge syndrome is caused either by inheritance of a defective chromosome 22 or by a new defect in chromosome 22 in the fetus.

The deletion means that several genes from chromosome 22 are missing in children with DiGeorge syndrome.

This technique uses DNA probes from the DiGeorge region on chromosome 22.

Although most children with DiGeorge syndrome do not inherit the chromosome deletion from their parents, they have a 50 percent chance of passing the deletion on to their own children.

Deletion-The absence of genetic material that is normally found in a chromosome.

A genetic disorder, it occurs because of the presence of an extra chromosome.

The extra chromosome in Down syndrome is labeled number 21.

One cell divides abnormally, creating a line of cells with an extra chromosome 21.

A piece of the number 21 chromosome then becomes attached to another chromosome.

Each cell still has 46 chromosomes, but the extra piece of chromosome 21 results in the signs and symptoms of Down syndrome.

Less than 25 percent of Down syndrome cases occur due to an extra chromosome in the sperm cell.

The majority of cases of Down syndrome occur due to an extra chromosome 21 within the egg cell supplied by the mother (nondisjunction).

Once this suspicion has been raised, genetic testing (chromosome analysis) can be undertaken in order to verify the presence of the disorder.

This testing is usually done on a blood sample, although chromosome analysis can also be done on other types of tissue, including skin.

In most cases of Down syndrome, one extra chromosome 21 will be revealed.

Nondisjunction-An event that takes place during cell division in which a chromosome pair does not separate as it should.

Prader-Willi syndrome (PWS) is a genetic condition caused by the absence of chromosomal material from chromosome 15.

Initially, scientists found that individuals with PWS have a portion of genetic material deleted (erased) from chromosome 15.

In order to have PWS, the genetic material must be deleted from the chromosome 15 received from one's father.

If the deletion is on the chromosome 15 inherited from one's mother, a different syndrome develops.

Over time, scientists realized that some individuals with PWS do not have genetic material deleted from chromosome 15.

Further studies found that these patients inherit both copies of chromosome 15 from their mother, which is not typical.

Normally, an individual receives one chromosome 15 from his or her father and one chromosome 15 from his or her mother.

A small number of patients with PWS have a change (mutation) in the genetic material on the chromosome 15 inherited from their father.

This mutation prevents certain genes on chromosome 15 from working properly.

The centromere separates the chromosome into long and short arms.

The short arm of a chromosome is called the p arm; the long arm and is called the q arm.

When genes in a certain region on a chromosome are silenced, they are said to be imprinted.

Individuals have two complete copies of chromosome 15.

One chromosome 15 is inherited from the mother, or is maternal in origin.

The other chromosome 15 is inherited from the father, or is paternal in origin.

There are several genes found on the q arm of chromosome 15 that are imprinted.

Seventy percent of the cases of PWS are caused when a piece of material is deleted, or erased, from the paternal chromosome 15.

This deletion occurs in a specific region on the q arm of chromosome 15.

These paternal genes must be working normally, because the same genes on the chromosome 15 inherited from the mother are imprinted.

If a child has PWS due to a sporadic deletion in the paternal chromosome 15, the chance the parents could have another child with PWS is less than 1 percent.

Maternal uniparental disomy for chromosome 15 leads to PWS because the genes on chromosome 15 that should have been inherited from the father are missing, and the genes on both the chromosome 15s inherited from the mother are imprinted.

Approximately 2-5 percent of patients with PWS have a change (mutation) in a gene located on the q arm of chromosome 15.

Methylation testing can detect the absence of the paternal genes that should be normally active on chromosome 15.

Chromosome analysis can determine if the PWS is the result of a deletion in the q arm of chromosome 15.

In some cases the deletion of material from chromosome 15 can be easily seen.

This testing is only recommended if the mother or father is known to have a chromosome rearrangement, or if they already have a child with PWS syndrome.

Maternal uniparental disomy-A chromosome abnormality in which both chromosomes in a pair are inherited from one's mother.

This indicates that the X chromosome is one of the locations for color blindness.

In 1997, the achromatopsia gene was discovered to reside on chromosome 2.

The researchers further concluded that there had been a mutation in the chromosome of the test respondents who did not have brown eyes.

The Danish blue-eyed genealogy study has led to the theory that blue eyes started with one person who had a mutation on their chromosome that shut off the production of melanin in their iris.

The Y chromosome passes from father to son in an almost unchanged state, so shared markers indicate a common patrilineal ancestry.

The most obvious limitation of this type of DNA test is that only men have a Y chromosome.

Paternal DNA testing focuses on the Y chromosome, which means it can only be performed on men.

Maternal DNA or mitochondrial DNA, is contained on the X chromosome.

However, unless there is a medical reason why a couple cannot have a child of a certain gender (such as a weak X or Y chromosome), your odds stay the same.

Women have two X chromosomes and men have an X and a Y chromosome.

Depending on which direction it is spun in, the X chromosome sperm rises to the top of the test tube.

Since the egg has no gender, it's the sperm's job to combine either a Y or X chromosome with egg's X chromosome to produce a boy (XY) or a girl (XX).

Male sperm, that which carries the Y chromosome, travels toward the egg faster than the female sperm.

Fragile X syndrome involves chromosomal problems on the X chromosome.

Prader-Willi syndrome is caused by dysfunction in the 15th chromosome.

Women over 35 years are more likely to have a child with chromosome problems.

The female eggs contain only X chromosomes (X is the female chromosome).

The male sperm contains either an X or Y (the Y chromosome makes a male).

Male children who inherit a fully mutated version of the FMR1 gene in the X chromosome will develop Fragile X, since males have just one X chromosome.

Mothers who have one mutated X chromosome and one normal copy have a 50 percent chance of passing the mutation to each child they bear, though they are very likely to show no symptoms of fragile X themselves.

Taking the latter first, Fragile X Syndrome is a genetic disorder carried by the X chromosome (the female one).

If she has a son, he only inherits one X chromosome, which means there is a high chance that he will have Fragile X Syndrome.

With nothing more than a drop of blood doctors can identify the chromosome and inform potential parents of the possibility.

For girls, with two X-chromosomes, the odds are that the "normal" X chromosome will compensate for the "fragile" one.

New medical developments are looking to help repair problems that stem from the disturbance on the X chromosome, but the approach is still being researched.

The scans revealed that a section of chromosome 16 and about 600,000 nucleotides were missing in the genomes of five children with autism.

The study identified genome regions may be linked to autism, including chromosome 6 and 20.

The variant is located near chromosome 5 and semaphorin 5A, which aid neuron and axon growth.