The term variation can be defined as the range of differences between individual organisms. This variation occurs within the species. For example differences between individual human beings. This variation is of two types:
Continuous Variation: In this variation all types of features have a normal distribution.
For example: Height of individual human beings, width of a leaf, weight of a cat, etc.
This image shows an example of continuous variation - height of individual human beings.
Discontinuous Variation: In this case, there are only a few features, which fall under the category of discontinuous variation.
For example: Different colour of flower in a single plant species, different types of blood groups in individual human beings, different types of ear lobe, etc.
This image shows an example of discontinuous variation - different colour of flower in a single plant species
The term heredity can be defined as the process of transferring the characters or the traits from the parents to their offspring. In this process of transformation, the characters gets transferred through the genes present in the DNA. These DNA's are present in the chromosomes, which are present in the nucleus of the cell. The transferring of the characters, includes the contribution of equal amount of genetic material from both the parents (mother and father) to their offspring.
Before moving into gene expression, let us know something about a gene.
What is a Gene?
A gene is a segment of the DNA, which contains all sorts of information that are required for coding some important functions. Hence a gene is called as a unit of information. Every cell in an organism have a similar set of genes. A gene is transferred from the parents to their offsprings. The term gene was coined by the scientist named Johann sen in the year 1909.
Gene expression is the activation of a gene, which results in a protein. Gene expression is the process by which the genetic information is used in the synthesis of a gene. This process is generally used in all eukaryote, prokaryotes and in viruses for generating the macromolecular machinery of life.
A code that contains all types of genetic information, which are present in the nucleotide sequences of DNA or RNA and are later translated into proteins by the living cells. These codes can be expressed either as RNA codons or DNA codons. These code instructs a gene to guide the cell to make a specific protein. A,T,G,C is the alphabetical letter of the DNA code. These letters stand for adenine, thymine, guanine and cytosine, which completely make up the nucleotide bases of DNA. Each and every code combines with these four chemicals for the synthesis of proteins.
DNA is called the blueprint of life as it contains all types of instructions for making proteins within the cell. It is very long polymer and the basic shape of the DNA is just like a twisted ladder. Hence it is also called as a double helices DNA. The backbone of the DNA molecule is alternating phosphates, deoxy Ribose sugar and nitrogenous bases. The information in DNA is stored as a code made up of four chemical bases: adenine (A), guanine (G), cytosine (C), and thymine (T).
Structure of DNA
It can be defined as the transformation of traits from the parents to their offspring. Everyone has two copies of every gene among which one inherited from the mother cell and another one is inherited from the father cell .
Causes of Variation and Evolution.
There are mainly two factors, which are responsible for variation and evolution of species. They are:
Genetic variation: In this case,difference in variation is mainly due to the presence of DNA inside the cells of an organism. The features of each species will be different in their colour, size and shape because they come from the parent with different alleles, which codes for different characteristics.
This image shows an example of genetic variation in the shape of tomatoes.
Environmental variation: In this case the difference in variation is mainly due to the external environmental conditions like water, light, temperature, wind, nutrients, pH of a soil, etc. For example: All features of plant species will be genetically identical but the differences are mainly seen in the colour of the flower, which is due to the effects of the environment.
This image shows an example of environmental variation in plant species, which are genetically identical but the differences are mainly seen in the colour of the flowers.