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Chromosomes Definition

A thread-like structure present in the nucleus of plants and animals is known as a chromosome. Each chromosome carries only one molecule of DNA (Deoxyribonucleic acid). DNA is transferred from one generation to the next generation, i.e., from parents to offspring through chromosomes.There are 23 pairs of chromosomes present in humans and 46 when counted singly.

Functions of chromosomes

Chromosomes are made up of proteins and enclose the DNA tightly around histones. Histones are spool-like protein structure which packs DNA around them so as to make them fit the self.If put together end to end, all the DNA of a single person, it would extend upto 6 feet; therefore, it gets extremely important to wrap DNA in such a way.For the growth and evolution of an organism and its proper functioning, cells keep dividing to create new ones and replace the old and unworking ones. This process of replacing the old and worn-out cells with new ones is known as cell division.Therefore, chromosomes play an important role in the process of ensuring that DNA is copied properly and evenly during this cell division. However, there is less probability of mistakes in DNA copying or cell division.

Any change in the structure of chromosomes or in their number from minor to the major may signify some serious health problems. For instance, when broken chromosomes or defective chromosomes are combined together, it sometimes leads to cancer and leukemia.

Chromosomes also play a very significant role in reproductive cells, i.e., sperm and eggs. These reproductive cells should carry the chromosomes of adequate structure. Improper number or structure of chromosomes may cause the baby to not develop properly or healthily. For example, generally, two copies of chromosomes are found in people, but the ones with down syndrome carry three copies of chromosomes 21.

Different types of chromosomes

All different living organisms have different numbers and structures of chromosomes; like bacteria have round or circular chromosomes, generally, 1 or 2 in number, and humans have linear chromosomes, generally in pairs. Only reproductive cells in humans do not have chromosomes in pairs. The Union of two reproductive cells creates a cell containing two copies of each chromosome. Further, the newly created cell divides numerous times, which leads to the creation of an individual completely mature with a complete set of chromosomes in pairs.

Other than linear chromosomes present in the nucleus, cells in humans and other living complex organisms are much more likely than those that appear in bacteria. It is found in mitochondria in a circular structure and is present outside the nucleus, which acts as its powerhouse. Earlier chromosomes were misconcepted as bacteria freely living with the potential to convert oxygen into energy.

The concept of centromeres

The region where the linear chromosomes are confined is known as the centromere. Centromere is not always located in the centre of the chromosome and is sometimes present at its end. Regions on the side of centromeres are called chromosome's arms. Centromeres help in the proper alignment of chromosomes when cell division is being conducted. Centromeres also act as the attachment for each replicated chromosome and are known as sister chromatids.

Chromosomes Definition

The concept of telomeres

The repetitive stretch of DNA present at the end of the linear chromosomes is referred to as telomeres. These telomeres protect the ends of the chromosomes. Sometimes, in many cells, telomeres lose a pinch of their DNA every time cell division takes place.When the telomere's DNA ends, the cell loses its replication ability and dies. Many cells, like white blood cells, contain some special enzymes which prevent the chromosomes to not to lose their telomeres as these cells divide very often. Due to their ability to retain telomeres, such cells live longer than others. Telomeres have a significant role in causing cancer in people. They generate the fuel which fosters its growth and makes it more dangerous and killing.

Inheritance of chromosomes

Offspring inherit a copy of every type of chromosome, one from its female parent and the other from the male parent. This concept of inheritance is the reason which backs the concept of children inheriting some qualities from their mothers and some from their fathers. Babies inherit mitochondrial DNA from the female parent only.

Different chromosomes in males and females

The only difference in the pair of chromosomes is the sex chromosomes. Males carry one X chromosome and another Y chromosome, whereas females carry both X chromosomes. When more or fewer chromosomes are inherited, serious problems can occur. Females having extra X chromosome copies are generally taller than average and carry some mental disability, and males with extra X chromosome copies are also taller than average and usually carry impaired fertility. Also, there is another syndrome associated with an imbalance in sex chromosomes which is known as turner syndrome. Women with this syndrome are usually short in height, and many of them do not go through puberty and carry heart and kidney issues. Females with this syndrome carry only one X chromosome.

X and Y chromosomes

X and Y are the terms that refer to human sex chromosomes whose combination specifies the person's gender or sex. Generally, females carry XX pairs of chromosomes, and the male carries XY pair of chromosomes. The sex of the person is known when the sperm fertilizes the egg and initiates the process of creating a life. Cells in the egg and sperm are known as gametes or sex cells, which show up as haploid (only one chromosome). Gametes are the result of meiosis cell division which further leads to the division of cells. Gametes in a female's egg are the X chromosomes, while the male's sperm carries half X and half Y chromosomes. Therefore, sperm is the variable factor in determining the sex of the baby. A Baby's sex totally depends upon the male chromosome as it will inherit only the X chromosome from the female parent. If it inherits the X chromosome from the male parent, it will lead to a baby girl, and if it inherits the Y chromosome from the male parent, it will lead to a baby boy.

Recent studies and research papers have declared that a human can carry a different combination of genes of sex chromosomes, especially people belonging to the LGBT category.

Structure of sex chromosome

Unlike other chromosomes, sex chromosomes, i.e., X and Y chromosomes, have relatively different structures. Generally, the X chromosome is longer than Y chromosome and carries atleast 100 more genes and is dominant as they have no counterpart in the other sex chromosome, chromosome Y. This is the rationale behind that any quality which is recessive in females will be shown or appear in males and is referred to as X-linked genes. Genes that appear in the Y chromosome are known as Y-linked genes. According to research and studies, the X chromosome is three times the Y chromosome when being talked about size. Also, the X chromosome contains an estimated nine hundred genes, whereas the Y chromosome contains fifty-five genes. SRY gene is the male-determining gene present in the Y chromosome. Any mutation in this gene will lead to the formation of female genitalia in the embryo even after having XY pairs of chromosomes.

Abnormalities in sex chromosomes

Full or partial chromosome deletion or even duplicated sex chromosome leads to abnormalities that lead to rarely lethal conditions depending upon gender. As told earlier, Turner syndromes in females occur due to the lack of an X chromosome which leads to heart problems or failures, short height, and incomplete or no development of ovaries. A syndrome due to three X is called triple X syndrome. Triple X chromosome is also known as Trisomy X syndrome, and its effect is found in about 1 in 1000 females. Mild symptoms or no symptoms are found in the person suffering from trisomy X syndrome. Sezier, kidney problems, behavioural problems and development of speech and language skills might get delayed are to the presence of some other important symptoms. Klinefelter syndrome disorder is commonly found in 1 in 650 males and is caused due by to increase in the number of X chromosomes. Until puberty, some people suffering from Klinefelter syndrome may stay undiagnosed due to mild symptoms. The percentage of affected males who do not come to know about their condition is around 75%. Klinefelter syndrome involves many symptoms like less amount of testosterone produced due to the small testes, due to which there can be a delay in puberty, breast development, infertility and decreased muscle mass.


Deoxyribonucleic Acid is the abbreviated form of DNA. It is present in each and every cell of the body, which holds the person's genetic information. DNA is made up of four chemical bases: adenine (A), cytosine (C), thymine (T), and guanine (G).


These are the building blocks of the body. Sometimes genes are included in the formation of proteins. Genes are only transferred from one generation to another. Babies receive their genes from their parents. They get one copy of the gene from each parent. According to reports, an estimated of 20 to 25000 genes are present in the body.

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