What is Genetics?

The significant branch in science which involves the study of genes, gene variations, and the organism's heredity is known as genetics. It is also used to study the involvement of a gene or set of genes in the health of an individual and how it prevents several diseases in a human being. Thus, genetics also creates an understanding of various medical conditions.      

"Somatic cell (A); Possible combinations of both parental chromosomes (red and green) (B); Gamete of the hybrid containing the chromosomes of one parental species (C)"


The nucleus in every cell contains genetic information about that particular cell in the body. This genetic information is partially obtained from the father and partially from the mother. Thus, genes are otherwise called units of heredity as they are constructed of DNA (deoxyribonucleic acid) molecules. Each gene has certain information required to carry out a specific role. Genes are ultimately responsible for heredity. Around twenty thousand genes exist in each chromosome with a pair of 23 chromosomes in the body. These genes contain only 2% of the DNA molecules from the whole genome. The term genetics was coined earlier to the term gene by William Bateson in 1905. The word gene was coined by Wilhelm Johannes in 1909.      

DNA is the macromolecule that contains genetic information and is made up of subunits called nucleotides. The bases such as adenine, guanine, thymine, and cytosine, a phosphate group, and a molecule of sugar link to form a nucleotide. The order of the nitrogenous bases decides a particular genetic code.     


The chromosomes contain the genes and exist in 23 pairs in the human body. The chromosomes present within the nucleus are smaller and have a thread-like structure. Among the total 23 pairs, 23 chromosomes are inherited or obtained from the father and the remaining 23 from the mother. A gene and chromosome can be stated with an example of a book, in which the chromosome can be compared to the book and the gene to its pages. The number of genes carried by each chromosome varies from cell to cell. The longer and thinner DNA strands coil up more tightly to form the chromosome. The structure of the chromosome includes a centromere that splits the chromosome into short and long arms.          

The chromosomes are classified as autosomes and sex chromosomes. The chromosomes starting from 1 to 22 are known as autosomes and the 23rd chromosome pair is considered a sex chromosome. The two sex chromosomes are represented by the letters X and Y. They play a significant role in deciding the sex of an individual. In women, X chromosomes are available as two copies and in men, one X and one Y chromosomes exist. Important: Sex chromosomes for males and females are XY and XX respectively.


The term inheritance is commonly associated with the word heredity which is defined as the mechanism by which the characteristics are transferred from generation to generation. Gregor Johann Mendel is known as the father of modern genetics due to his discoveries on heredity principles.       


The variation is the extent of dissimilarity observed between children and their parents. The study of variation in genetics concludes several individual characteristics. It deals with the morphological, behavioural, physiological, and cytological characters of an individual that belong to the same kind of species. The significant factors that lead to these variations are listed below:      

  • Gene mutation due to the influence of the ecosystem on the organisms.      
  • Rearrangement of the genes or chromosomes.      
  • Crossing over mechanism.     

Genetic Disorders      

Genetic disorders can result from several causes. In terms of chromosomes, the disorder occurring in the autosomes is referred to as autosomal conditions, and the disorder occurring in the sex chromosomes is named X-linked. The genetic disorder is categorized by the way it is transferred among the families and its causes. Thus, a genetic disorder can be categorized as either recessive or dominant.      

Types of Genetic Disorders 


DNA mutations occurring in only a copy of a gene are capable of causing disease in an individual, such conditions are referred to as dominant diseases. In this case, if a mother or father is affected by a disease, their children can inherit the particular gene which is mutated with a 50% probability.      


For this type of disease, the gene copies obtained from both the mother and father must be mutated. A copy of a mutated gene present in both parents develops around a 25% chance of the child inheriting the disease. In this recessive disease, parents are not infected by the disease, rather they act as a carrier for such mutated genes. Thus, there is a probability that a child can be infected with a disease, but the parents of the child are not infected with the same.  

Single Gene Disorders 

The genetic disease caused due to the mutation in only one of the genes in an individual is known as a single gene disorder. The mutation occurring in the chromosome can directly take place in the sperm or egg cell or can be inherited from the parents. The single gene disorder can be X-linked or autosomal. Sickle-cell disease is an example of a singlegene disorder, in which a gene mutation occurs in chromosome 11. Fragile X syndrome is an example of an X-lined disorder of a single gene.

Chromosomal Abnormalities   

The abnormalities in the chromosomes’ number, their shapes, and their availability are referred to as chromosomal abnormalities. Trisomy and monosomy are two different conditions in the abnormality of chromosomes that depend upon the number of chromosomes. Deletion, duplication, and inversion are a few of the terms used to represent chromosomal abnormalities in terms of the variations in the shape or availability of the chromosomes. Apart from these conditions, certain other multifactorial diseases are categorized as complex conditions. These diseases are usually caused by the factors associated with the environment and genes. Certain types of hereditary cancer such as hereditary breast or ovarian cancer are examples of multifactorial diseases.   

"Single-chromosome mutations: deletion (1), duplication (2), and inversion (3)"

Context and Applications     

This topic is significant in the professional exams for both undergraduate and graduate courses, especially for;

  • Bachelors in Genetics, Biochemistry and Molecular biology
  • Masters in Genetics, Biochemistry and Molecular biology
  • Masters in Ecology and Evolutionary biology
  • Masters in Biological Sciences
  • Masters in Biotechnology

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