Facts about chromosomes you need to know & bull; hello healthy

Although not as familiar as DNA, chromosomes are actually related to this one molecule. However, do you know exactly what a chromosome is? For more details, let's take a look at some of the following facts.

What are chromosomes?

Chromosome comes from the Greek word, viz chroma and soma. Chroma means color, meanwhile soma means body. Scientists give it this name because this molecule is a cell or body structure that consists of certain colors when viewed under a microscope.

This molecule was first observed in the late 1800's. However, at that time the nature and function of this cell structure were not yet clear. In the early 1900's, Thomas Hunt Morgan then re-examined this section. Morgan discovered the relationship between chromosomes and inherited traits in living things.

With this, it can be concluded that chromosomes are tightly coiled collections of DNA located in the nucleus (cell nucleus) of almost every cell in the body. This DNA collection is a thread-like molecule that carries hereditary (derivative) information from height to skin color to eye color.

This molecule is made of protein and a DNA molecule which contains the genetic instructions for an organism that is passed down from parents. In humans, animals, and plants, most of the chromosomes are arranged in pairs in the nucleus of the cell.

Normally, humans have 23 pairs of chromosomes in their body or the same as 46 copies. However, in plants and animals the numbers vary widely. Each DNA collection has two short arms, two longer arms, and one centromere in the center as the center.

Chromosome function

The unique structure of chromosomes causes DNA to wrap around coil-like proteins called histones. Without such coils, the DNA molecules would be too long to fit into the cell.

As an illustration, if all the DNA molecules in a human cell were removed from the histones, it would be about 6 feet long or the equivalent of 1.8 meters.

In order for an organism or living thing to grow and function properly, cells must continue to divide. The goal is to replace old damaged cells with new ones. During this process of cell division, it is important that DNA remains intact and evenly distributed between cells.

Well, chromosomes play an important role in this process. The reason is, this molecule is responsible for ensuring that DNA is accurately copied and distributed in most cell divisions. But sometimes, there is still the possibility that this DNA collection made mistakes in the process of division.

It is the change in the number or structure of the DNA collection in cells that is new to causing serious problems. For example, certain types of leukemia and some other cancers are caused by damage to this DNA collection.

In addition, it is also important that the egg and sperm contain the right number of chromosomes with the correct structure. If not, the resulting offspring may also fail to develop properly.

The chromosomes of every living thing are not the same

In number and shape, these DNA collections vary greatly from one living thing to another. Most bacteria have one or two circular chromosomes. Meanwhile, humans, animals, and plants have linear chromosomes arranged in pairs in the cell nucleus.

The only human cells that do not contain a chromosome pair are reproductive cells or gametes. These reproductive cells carry only one copy of each.

When two reproductive cells unite, they become a single cell which contains two copies of each chromosome. These cells then divide to finally produce a complete adult individual with a complete set of paired chromosomes in almost all of its cells.

Circular DNA collections are also found in mitochondria. Mitochondria are the breathing areas of cells. This part is later tasked with burning glucose and producing energy needed by the body.

Within the mitochondria, these DNA collections are much smaller in size. This circular DNA collection, located outside the cell nucleus in the mitochondria, functions as the cell's powerhouse.

The way of chromosome inheritance

In humans and most other living things, one copy of each DNA collection is inherited from a female and a male parent. Therefore, every child who is born must inherit some of the characteristics of his mother and father.

However, this inheritance pattern is different for the small DNA assemblages found in mitochondria. Mitochondrial DNA is always inherited from the female parent or egg cells only.

Men and women have different chromosomes

Apart from being physically different, men and women also have different sets of DNA. These different sets of DNA are called sex chromosomes. Females have two X chromosomes in their cells (XX). While men have one X and one Y (XY).

A person who inherits too many or too few copies of sex chromosomes can cause serious problems. In women who have extra copies of the X chromosome more (XXX) can trigger mental retardation.

Meanwhile, men who have more than one X chromosome (XXY) will experience Klinefelter syndrome. This syndrome is usually characterized by small, undescended testicles, enlarged breasts (gynecomastia), lower muscle mass, and larger hips like women.

In addition, another syndrome caused by an imbalance in the number of sex chromosomes is Turner syndrome. Women with Turner syndrome are characterized by only having one X chromosome. They are usually very short, flat chested, and have kidney or heart problems.

Types of chromosomal abnormalities

Chromosomal abnormalities are usually divided into two broad groups, namely numerical and structural disorders.

Numerical abnormalities

Numerical abnormality occurs when the number of chromosomes is less or more than it should be, namely two (a pair). If a person loses one of them, this condition is called monosomy in the group of DNA collections concerned.

Meanwhile, if a person has more than two chromosomes the condition is called trisomy.

One of the health problems caused by numerical abnormalities is Down syndrome. This condition is characterized by mental retardation in the sufferer, a distinct and distinctive facial shape, and poor muscle strength.

People with Down syndrome have three copies of chromosome 21. That's why it's called trisomy 21.

Structural abnormalities

Structural abnormalities usually change due to several things, namely:

• Deletion, part of the chromosome is lost.
• Duplication, a portion of the chromosomes multiply to produce additional genetic material.
• Translocation, some chromosomes are transferred to other chromosomes.
• Inversion, a part of the chromosomes is damaged, reversed, and reconnected which makes the genetic material reverse.
• Ring, part of the chromosomes are damaged and form a circle or ring.

Generally, most cases of structural abnormalities occur due to problems with the egg and sperm. In this case, abnormalities appear in every cell of the body.

However, some abnormalities can also occur after fertilization so that some cells have abnormalities and some do not.

This disorder can also be passed down from parents. For this reason, when a child has an abnormality in his DNA collection, the doctor will check the DNA collection of his parents.

Causes of chromosomal abnormalities

Reporting from the National Human Genome Research Institute, chromosomal abnormalities usually occur when there is an error in the cell division process. The process of cell division is divided into two, namely mitosis and meiosis.

Mitosis is a division process that results in two duplicate cells from the original cell. This division occurs in all parts of the body except for the reproductive organs. Meanwhile, meiosis, is cell division that produces half the number of chromosomes.

Well, in both these processes an error can occur which causes too few or too many cells. Errors can also occur while this DNA pool is being duplicated or duplicated.

In addition, other factors that can increase the risk of this DNA collection abnormality include:

Mother's age

Women are born complete with eggs. Some researchers believe that this disorder can arise due to changes in the genetic material of the egg with age.

Usually, women with older age have a higher risk of having a baby with chromosomal abnormalities, compared to those who become pregnant at a younger age.

Environment

It is possible that environmental factors play a role in the emergence of genetic errors. However, further evidence is still needed to find out what influenced it.

Diseases caused by chromosomal abnormalities

Down syndrome

Down syndrome is a genetic disorder which is also referred to as trisomy 21 condition. This condition is one of the most common genetic birth defects caused by the addition of chromosome 21. As a result, babies have 47 copies of the chromosome, whereas humans normally only have 46 copies ( 23 pairs).

One of the strongest factors causing this problem is the mother's age at pregnancy. Usually the risk will increase every year after the mother is 35 years old.

Children with Down syndrome can usually be easily recognized by their physical characteristics. Here are some common signs of Down Syndrome children:

• Eyes that tend to tilt upwards
• Small ears that are usually slightly folded
• Small mouth size
• Short neck
• Joints tend to be weak

Turner Syndrome

This condition is a genetic disorder that usually occurs in girls. This occurs when a child loses one chromosome, so there are only 45. Usually children with Turner syndrome are shorter than their peers.

In addition, some of the other symptoms that characterize Turner's syndrome include:

• Has a wide neck with skin folds on the sides.
• There are differences in the shape and position of the ears
• Flat chest
• Have a lot more small brown moles on the skin than usual
• Small jaw

Klinefelter's Syndrome

Klinefelter's syndrome is also known as the XXY condition in which men have an extra X chromosome in their cells. Usually, babies with this syndrome have weak muscles. Therefore, the development tends to be slower than the others.

During puberty, men with XXY syndrome usually don't produce as much testosterone as other boys. In addition, they also have small, infertile testes.

This condition makes the child less muscular, has less facial and body hair, and even breasts that are larger than normal.

Trisomy 13 and 18

Trisomy 13 and 18 are genetic disorders that result in birth defects. Trisomy 13 means a baby born has 3 copies of chromosome number 13. Trisomy 13 is called Patau's syndrome.

Meanwhile, a child who has three copies of chromosome 18, or trisomy 18, is called Edwards syndrome. Generally, children who have both conditions will not survive until the age of one.

Babies with trisomy 13, or Patau's syndrome, usually have:

• Low birth weight
• Small head with slanted forehead
• Structural problems in the brain
• The size of the eyes are close together
• Cleft lip and palate
• The testes do not descend into the scrotum

Meanwhile, babies with trisomy 18 (Edwards syndrome) are characterized by:

• Failure to thrive
• Little head
• Small mouth and jaw
• Short sternum
• Hearing problems
• Arms and legs are bent
• The spinal cord is not completely closed (spina bifida)

How to detect chromosomal abnormalities in the fetus

To detect chromosomal abnormalities in the fetus, there are several tests that can usually be done. This test is quite important because the abnormalities that appear can affect the development of the baby. There are two types of tests that are usually done, namely:

Screening test

This test is done to look for signs that your baby is at high risk of developing an abnormality. However, screening tests cannot determine with certainty that a baby has a particular disorder.

Even so, this test has no adverse impact on both mother and baby. The following are the different types of screening tests that can be done:

The first trimester combined screen (FTCS)

This test is performed with an ultrasound scan of the baby at 11 to 13 weeks of gestation. Apart from ultrasound, blood tests will also be performed at 10 to 13 weeks of pregnancy.

This procedure combines the results of ultrasound and blood tests with facts regarding the mother's age, weight, ethnicity, smoking status.

The triple test

This one test is done in the second trimester of pregnancy, which is between 15 and 20 weeks of age. This procedure is done to measure the levels of certain hormones in the mother's blood. Usually this test is done to see the risk of Down syndrome, Edward's syndrome, Patau's syndrome, and neural tube defects (spina bifida).

Noninvasive Prenatal Testing (NIPT)

NIPT is a prenatal screening to look at DNA from the baby's placenta in the mother's blood sample. However, screening such as NIPT only determines the likelihood. This test cannot determine with certainty whether the baby will have a chromosomal abnormality or not.

Although we can't determine with certainty, according to research published in the BMJ Open, this test has an accuracy of 97 to 99 percent for detecting Syndome Down, Patau, and Edward.

Later, the results of this NIPT screening will help doctors determine their next steps, including whether you need to do a diagnostic test such as Chorionic Villus Sampling (CVS) or amniocentesis, or not.

Diagnostic test

This test is done to determine whether your baby has a chromosomal abnormality or not. Unfortunately, diagnostic tests are quite risky to cause miscarriage. The following are the different types of diagnostic tests that can be done:

Amniocentesis

Amniocentesis is a procedure used to obtain a sample of the amniotic fluid that surrounds the fetus. This test is usually performed on women between 15 and 20 weeks of gestation.

However, women who need to undergo this test usually prefer those who have a high risk, such as aged 35 years and over, or have an abnormal screening test.

Chorionic Villus Sampling (CVS)

This procedure is done by taking a cell or tissue sample from the placenta for testing in the laboratory. Cells or tissue from the placenta are taken because they have the same genetic material as the fetus. The cell or tissue can also be tested for abnormalities in the DNA collection.

CVS cannot provide information about neural tube defects, such as spina bifida. Therefore, after performing CVS, the doctor will perform further blood tests at 16 to 18 weeks of gestation.