Heredity and Evolution | Key-Terms


These are the thin thread-like structure, present in the nucleus, which carries the gene. They are mainly composed of DNA and proteins.


These are the unit of inheritance, occurring at a specific location on a chromosome. A single gene may be made up of thousands of DNA bases.


Deoxyribonucleic acid. It consists of nucleotides and is the main constituent of chromosomes. It is the carrier of genetic information.

Amino acids

These are the organic molecules that are the building block of protein. There are 20 different types of amino acids in living beings that are linked via a peptide bond.


These are bio-macromolecules consisting of one or more chain of amino acids, performing various functions like enzymes, antibodies, hormones, structural components, etc.


These are the alternate forms of a gene.


A condition where a particular trait is controlled by more than two alleles OR A condition in which a gene occurs in more than two alleles.

Dominant allele

An allele that masks the presence of a recessive allele in the phenotype. Dominant alleles for a trait are usually expressed if an individual is homozygous dominant or heterozygous.

Recessive Allele

An allele, whose expression is masked by the presence of a dominant allele. The recessive alleles are expressed only in the homozygous recessive condition (aa).


The situation where neither allele is dominant or recessive, both of them appear in the phenotype.

Incomplete dominance

The situation where the phenotypic expression of one allele for a specific trait is not completely expressed over the other allele. This results in an intermediate trait.

F1 Generation

The First filial generation. These are the offspring of the first generation. The subsequent generations are referred to as F2, F3, F4, etc.


An offspring of a cross between two genetically different parents.


A genotype consisting of two different type of allele for a gene (Aa).


A genotype consisting of the same type of allele for a gene. The individual may be homozygous dominant (AA) or homozygous recessive (aa).

Punnett square

It is a diagram to predict the outcome of a particular cross.

Principle of independent assortment

During gamete formation, a segregating pair of alleles assorts independently of each other.

Principle of segregation

During gamete formation, each of the gamete receives one of the pairs of gamete, selected randomly.


The genetic makeup of an individual.


The observable characteristics of an organism. It is the result of the expression of the genotype.

Homologous chromosomes

These are the chromosomes that are paired during meiosis having similar size and shape. One of these chromosomes is of paternal origin while the other has a maternal origin. These chromosomes have the same genes but not necessarily the same alleles.

Test cross

For organisms with unknown genotype, test cross is performed for the organism in question with an organism with the homozygous recessive trait, to find out if the organism is homozygous or heterozygous for the trait.


Genetic changes that get accumulated in a population over time that might lead to speciation.

Gene flow The transfer of genes from one population to another population by migration, possibly leading to altered allele frequency.
Gene pool The sum total of all different alleles in a population at a given time.
Genetic drift Random change in a gene frequency of a small population that provides diversity without any survival disadvantage.
Mutation A change in the DNA at a particular location in the chromosome of an organism.
Karyotype A photo captured through a microscope of all the chromosomes in a person, arranged from chromosome 1 through the sex chromosome.

9 thoughts on “Heredity and Evolution | Key-Terms

  1. K.VINAY says:

    Sir.. . Thanx a lot .. .. Its so worthful, making our preparation easier and effective…. They are bearing transparent words thus r easy 2 assimilate… Hope u would soon publish bumf related 2 other chapters… Well done sir… ATB for ur ambition.

    Liked by 1 person

  2. Sidharth Uttarakabat says:

    Sir…thanks a lot for providing us such a wonderful information which made me to understand the key terms easily. …and I believe all will like this site….and I hope u will develop this site more !!!
    Well done sir …. and we hope a lot from u…..!!!

    Liked by 1 person

    • Biswal RK says:

      Amoeba has no definite structural organization. 

      Leishmania has whip like structure at one end of the cell.

      Amoeba fission can take place in any one plane.

      Leishmania fission takes place in a definite orientation.


  3. Anonymous says:

    Thx a lot sir……..It’s very helpful 2 us…..D terms n concepts which we 4got ………NW it became easy 4 remember without searching any book………Thx sir…..

    Liked by 1 person

Leave a Reply

Fill in your details below or click an icon to log in: Logo

You are commenting using your account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s