Biology

Your DNA determines who you are

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Have you ever asked yourself what exactly determines who you are? Why are you in the way that you are? Every single feature of your face, every detail of your body, every process that takes place in your body, including your mind, is determined by your genetic information. Everything is encoded and kept in the nucleus of each cell in your body.

The genetic information is stored in structures called chromosomes. Each chromosome contains of one DNA molecule and proteins. The deoxyribonucleic acid is in fact polymer. That is a large molecule that is made out of smaller, repeating molecules called monomers. The monomers of DNA are called nucleotides. Nucleotides are the same except the type of nucleobases. There are four types of nucleobases, therefore DNA is made out of four different nucleotides – Adenine (A), Guanine (G), Thymine (T) and Cytosine (C). 

Every DNA molecule contains two strands, that run in opposite directions and are connected to each other by binding the nucleobases from the opposite nucleotides. Always A from one strand binds with T from the opposite strand and G from one strand binds with C from the opposite one. This is the way how genetic information is stored. The sequence of those nucleotids makes up the whole diversity of proteins and therefore of organisms. Yes, it is only four different nucleotides, but they are billions on one DNA molecule and the human genome has 46 chromosomes ( 23 different chromosomes that form pairs).

Perhaps you  are asking how all of this has to do with the way you look and you think. Here is the answer. DNA has structural and functional parts called genes. Each gene has the information for a specific protein ( there are special techniques in different cells how from one simple gene similar but still distinguishing from each other proteins could be produced). So each gene has a specific nucleotides sequence, which is first transcribed into special molecules called RNA. The type of RNA that carries the information for synthesizing a protein is called messenger RNA or mRNA. The messenger RNA is then translated into a protein. This happens by the ribosomes which are special organels in the cells. The sequence of three nucleotides from mRNA codes one amino acid from the protein ( proteins are polymers made out of amino acids). For example, the sequence AGA stands for the amino acid Arginine.

This is how different proteins are produced in the cell. Proteins are the polymers that determine the structure and functions of each cells, tissues, organs. It is considered that the difference between people is due to the difference in the proteins that build them up.


Chromosome abnormalities

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What are chromosome abnormalities?

These are changes in the normal number and structure of the chromosomes. Most of them have either lethal outcome or cause different changes to the normal structure of the body. Some of them cause changes in the brain such as mental retardation.

What types of chromosome abnormalities are there?

Chromosome abnormalities could be two types -  numerical and structural.

In the numerical chromosome abnormality there is a difference in the usual number of chromosomes. There are two types – euploidy and aneuploidy. Euploidy is when the cells have a different amount of chromosomes which is even to the normal haploid state of the cell. For example, human cells are diploid (2n).  Euploidy is when the cells are triploid (3n), tetraploid (4n), etc. The number increases with a “n”. Aneuplody is when the number changes because of additional or missing chromosomes. For example, human reproductive cells are haploid (n). However, during cell division chromosomes could not divide normally and as a result there are cells with additional chromosome (n+1) or cells which are missing a chromosome (n-1). The first case is called trisomy and the second monosomy. There are cells which could have a whole pair of chromosomes as addition or missing. The first case is tetrasomy (2n+2) and the second nullisomy (2n-2).

Structural abnormalities are due to change in the structure of chromosomes. They occur because of chromosome breakage. This is caused by different factors of the environment. As a result of this breakage a chromosome could lose a part of its structure, receive an additional part or exchange parts between two homologous chromosomes. There is also the possibility of reversing a part inside the chromosome. Losing a part of the chromosome is referred as deletion, having a duplicate part similar to another one of the chromosome is called duplication. Reversing a part of the chromosome is called inversion. Exchanging parts between homologous chromosomes is called translocation.

What causes such abnormalities?

All of these abnormalities are due to changes in the cells, mainly in the mitotic spindle. This is a really important temporary structure, which forms only during cell divisions. Its importance is to make sure that chromosomes divide normally and each daughter cell receives the needed number. Chromosomal abnormalities are caused because of factors, which affect the organism. For example, radiation, viruses, bacterias, drugs and others.