Chromosome abnormality

Inside our bodies, we have tiny parts.

These parts hold our plans for growing. Sometimes, a part is missing. Other times, there is an extra part.

This can happen when cells make new copies of themselves. A part might also break or change shape. This can happen because of things in the world around us. Some changes are passed from parents to children. Other changes happen as a person grows up. These changes can be harmless or cause health problems.

Our bodies use tiny parts called chromosomes to hold our plans.

Sometimes, these parts change. This is called a chromosomal abnormality.

One way this happens is with numbers. A person might have too many or too few chromosomes. For example, Down syndrome happens when there is an extra copy of chromosome 21. This is called trisomy 21.

Another example is Turner syndrome. In this case, a person has only one X chromosome.

Another way is with the shape of the parts. A piece might break off or turn upside down. This is called a structural abnormality. Some changes are "balanced." This means no parts are lost or gained. These changes can be harmless.

These changes can happen in different ways. Some are passed from parents to children. Others happen as a person grows. They can come from mistakes when cells divide. They can also come from things in the environment.

Doctors use a karyotype to study these parts. A karyotype is a full set of chromosomes.

Our bodies rely on chromosomes to hold our genetic plans. Sometimes, these chromosomes change in unexpected ways. This is called a chromosomal abnormality. These changes can involve the number of chromosomes or their physical shape.

An abnormality can be a missing, extra, or irregular piece of DNA. While some changes lead to health conditions, others may be harmless. Scientists study these changes to understand how life works.

Numerical abnormalities happen when there is an unusual number of chromosomes. One common type is called aneuploidy. This occurs when a person is missing a chromosome or has an extra one. For example, trisomy 21 is when there is an extra copy of chromosome 21. This causes Down syndrome.

Another type is monosomy, where a chromosome is missing. Turner syndrome is an example of this.

In these cases, the cell might have three sets of chromosomes, called triploid, or even four sets, called tetraploid.

Structural abnormalities happen when the shape of a chromosome changes. This often occurs if a piece breaks and realigns incorrectly. Some changes are unbalanced, meaning genetic information is lost or gained. A deletion is when a piece is missing.

A duplication is when a piece is copied twice. There are also insertions, where a piece moves to a new spot. Some changes are balanced, meaning no information is lost. An inversion happens when a piece turns upside down before reattaching.

Translocations occur when pieces move between two different chromosomes.

These changes can happen in several different ways. Some occur during cell division when chromosomes fail to separate properly. This is often called nondisjunction. Other changes can be caused by environmental factors. For example, exposure to things like tobacco smoke or certain chemicals can increase risks.

Some abnormalities are present at birth and come from the egg or sperm. These are called constitutional abnormalities. Others are acquired during a person's lifetime. These acquired changes happen in specific cells and are not passed to children.

Understanding how these changes move through families is very important. Some patterns are called Mendelian inheritance. For example, autosomal dominant traits can appear in every generation.

Other traits, like X-linked recessive ones, affect males more often.

There is also mitochondrial inheritance, which is passed only from a mother.

Doctors can use a karyotype to see these patterns. A karyotype is a full set of an individual's chromosomes. By comparing it to a typical set, they can find exactly what changed.

A chromosomal abnormality is a change in the DNA of a chromosome. This change might involve an extra, missing, or irregular portion of genetic material. These anomalies are often called chromosomal disorders or chromosomal aberrations when they lead to specific health conditions. However, not all abnormalities cause disease. Some structural changes are considered balanced, meaning the total amount of genetic information remains complete.

Numerical abnormalities involve an atypical number of chromosomes. A common form is aneuploidy, where an individual lacks a chromosome from a pair, known as monosomy, or has an extra one, known as trisomy. For example, trisomy 21 involves an extra copy of chromosome 21 and causes Down syndrome.

Monosomy can also occur, such as in Turner syndrome, where an individual has only one X sex chromosome.

Beyond aneuploidy, polyploidy occurs when cells contain more than two sets of chromosomes. This includes triploidy, with three sets, or tetraploidy, with four sets.

These numerical errors often happen during cell division. During meiosis, the process that creates sperm and egg cells, errors like nondisjunction can occur. Nondisjunction is when replicated chromosomes fail to separate properly. This results in germ cells that have either an extra or a missing chromosome. Tetraploidy can arise from errors during mitosis, which is regular cell division. Processes like cytokinesis failure or mitotic slippage can lead to these extra sets of chromosomes.

Structural abnormalities happen when the physical shape of a chromosome is altered. This usually occurs due to breakage and improper realignment of segments. Unbalanced rearrangements result in a loss or gain of genetic information. Deletions occur when a portion is missing, such as in Wolf–Hirschhorn syndrome. Duplications involve extra genetic material, like in Charcot–Marie–Tooth disease type 1A. Insertions happen when a piece of one chromosome is moved into another.

Other structural changes are balanced, meaning no genetic information is lost. Inversions occur when a segment breaks, turns upside down, and reattaches. Translocations involve the movement of segments between different chromosomes. A reciprocal translocation is an exchange between two chromosomes. A Robertsonian translocation occurs when two chromosomes break at their centromeres and fuse.

Other complex shapes include ring chromosomes, where the ends break off and form a circle, and isochromosomes, which are mirror-image copies of a chromosome segment.

Chromosomal abnormalities can be inherited or occur spontaneously. Constitutional abnormalities are present from the beginning of development. These often arise from errors in the egg or sperm and are found in every cell of the body. Spontaneous changes, called de novo mutations, occur without prior inheritance. These can emerge during the formation of germ cells or during embryonic development. Some individuals exhibit genetic mosaicism, where they possess two or more genetically distinct cell populations.

Inheritance patterns follow specific rules known as Mendelian inheritance. Autosomal dominant traits, like Huntington's disease, appear in every generation if one parent is affected. Autosomal recessive traits, such as cystic fibrosis, require both parents to be carriers. X-linked inheritance involves the X chromosome and can be dominant or recessive. In X-linked recessive patterns, males are more frequently affected.

There is also mitochondrial inheritance, which is passed only from the mother to her offspring.

Environmental factors can also play a role in these changes. Exposure to certain hazards may increase the risk of aneuploidy in sperm. For example, tobacco smoking or exposure to benzene and insecticides can increase this risk. These factors are often associated with increased DNA damage. To identify these issues, scientists use a karyotype. This is a full set of an individual's chromosomes, which is compared to a typical karyotype to find specific errors.