Genetics are traits inherited from one's family. As a branch of science, it studies genes, heredity and variations.

Genetics are traits inherited from one’s family. As a branch of science, it studies genes, heredity and variations.


Views on heredity date back thousands of years. It was known that some characteristics of living things passed between generations, although they were not revealed as clearly as they are today.

Scientists from ancient civilizations such as Hippocrates and Aristotle have studied human semen and its shaping.

Scientific studies on heredity that have survived to the present day begin with Gregor Mendel in the 1800s. As a result of his observations on plants for many years, Mendel revealed that some characteristics of plants show hereditary transmission and that there is a mathematical expression for this. The term genetics was first coined by William Bateson in 1906.

Inheritance features: 

Inheritance is provided by genes in living organisms. The genetic material is stored in DNA (deoxyribonucleic acid) in plants, animals, fungi and bacteria, and in RNA (ribonucleic acid) or DNA in viruses. Genes are linear sequences of nucleotides, the chemical building blocks of DNA and RNA.


DNA is found in the nucleus of nucleated cells and in the cytoplasm of nonnucleated cells.

DNA consists of 4 types of nucleotides. These:

  • Adenine (A),
  • Guanine (G),
  • Cytosine (C),
  • thymine ( T ) .

The sequence of these four nucleotides creates genetic information.

DNA is in a double-stranded helical structure. Nucleotides complement each other in this double helix. Thymine is opposite to Adenine and Cytosine is opposite to Guanine. Guanine-Cytosine and Adenine-Thymine are linked by hydrogen bonds.

Adenine and Guanine have a single ring structure called purine , while Thymine and Cytosine have a single ring structure called pyrimidine . Mathematically, the amount of purine is equal to the amount of pyrimidine, the amount of Adenine is equal to the amount of Thymine, and the amount of Cytosine is equal to the amount of Guanine.

Nucleotides in DNA are used to form amino acids, and amino acids are used to form proteins. The sequence of amino acids in the protein determines the shape of the protein and therefore its function. The protein is produced in the cell cytoplasm.

All living things are composed of these four nucleotides, but the number and sequence of these nucleotides differ among living things. This difference creates the difference between living things.


It carries the information in DNA from the nucleus to the cytoplasm and initiates protein synthesis in the cytoplasm. RNA is synthesized from DNA. There are three different types:

  • m-RNA: It is messenger RNA. It transmits the information on how to arrange amino acids in the cell from DNA to the ribosome.
  • t-RNA: It is the carrier RNA. It pairs with specific amino acids in the cytoplasm and delivers them to the ribosomes.
  • r-RNA: It is the most abundant RNA in the ribosome.


It is a long DNA molecule organized into genes. It is found in all nucleated cells. It can be seen with an electron microscope.

They are the units that provide heredity in living things. It consists of DNA and protein.

The shape, size and number of chromosomes differ between living species. Chromosome number, shape and size are fixed within the species and are passed on through generations. For example, the frog has 26 chromosomes, the mouse 42, and the dog 78.

Humans have 46 chromosomes. One pair of 23 pairs of chromosomes determines sex. The sex chromosomes are shown as XX in females and XY in males. Of the 46 chromosomes, 23 are inherited from the mother and 23 from the father. If there is a change in the number or shape of chromosomes, it appears as a genetic disease.

For example, Down Syndrome (trisomy 21) develops when there are three chromosomes numbered 21, which should normally be even in number, that is, a total of 47 chromosomes. The advanced age of the mother’s gestational age poses a risk for this chromosomal disorder.

Changes in the number of sex chromosomes appear as chromosomal diseases. Kleinfelter Syndrome develops when the sex chromosome, which should be XY in men, is XXY, that is, one more chromosome. Turner Syndrome develops in cases where the sex chromosome, which should be XX in women, is X, that is, one missing.

In some cases, structural defects such as displacement (translocation), deletion (deletion), increase (duplication), inversion (inversion-ring formation) are also seen in chromosomes. All these structural changes appear as genetic diseases.