Variation of Population

Evolution is the cumulative changes in the characteristics of population or organisms occurring in the course of successive generations related by descent. Variations are differences in traits or characteristics between individuals of the same species. There are genetic and physical variations.

  1. Genetic variations are those which are controlled by genes and can be inherited
  2. Phenotypic variations may be produced by genes but can also be caused by the environment, or a combination of both genes and the environment.

Variation can also be continuous or discontinuous.

  1. Continuous variation
    • Continuous variation is influenced by a combination of both genetic and environmental factors.
    • They have no distinct categories, resulting in a range of phenotypes between two extremes; examples include body length and body mass, height, counter-shading on a red-green apple fruit.
    • Continuously variable characteristics are strongly influenced by the environment. A person may inherit genes for tallness but they may not get enough food to grow tall.
  2. Discontinuous variation
    • This variations take the form of distinct, alternative phenotypes with no intermediates
    • Discontinuous variation cannot usually be altered by the environment.
    • Examples include blood group, The ability to roll the tongue, eye colour, seed shape in peas and seed colour in peas.

Examples of continuous variation in plants

  1. height of plants
  2. shape of the body parts
  3. size of petals and sepals
  4. Root size

Examples of Discontinuous Variation In Plant

  1. Colour of leaves
  2. colour of flowers
  3. colour of fruits
  4. shape of seeds and fruits
  5. colour of seeds

Morphology Variation

Variations in physical traits or outward appearances in organizations are known as morphological variations. Examples include:

  1. Height: If you measure the heights of all the students in your class that are of the same age, there is likely to be a steady graduation from the students who are very short to those who are very tall.
  2. Mass: Variations in weight can be due to genetic heredity or certain environmental factor such as lifestyle, diet or whether one is affected by an illness.
  3. Facial features: Although humans general look similar in physical form, our facial features vary. Some of our facial features like our nose or mouth resembles our parents but none looks exactly like theirs. The shapes of our face can range from oblong, round to squarish.
  4. colour of the eye: Eye color varies from person to person. It could be amber, brown, red, grey, green or blue. This continuous variation depends on the amount of melanin present in the iris of the eye. Brown eyes contain high levels of melanin while blue eyes contain low level of melanin.
  5. finger print patterns: Fingerprints are patterns formed by the ridges in the dermis of the skin on our fingertips. Due to small variations in the fingerprints of different individuals, each person has a unique finger-print. Variations in finger prints can be broadly classified into:
    • loop
    • whorl
    • arch
    Loops are the most common type, accounting for about 65 percent of all fingerprints. Whorls account for 30 percent of fingerprints, and arches for 5 percent. Despite these broad patterns, each individual has a unique set of fingerprints, which can be used as a means of personal identification.
    6. Finger Print Pattern Diagram

Physiological Variation

Physiological or discontinuous variation is the difference in the ways individuals of the same species behave or react to conditions in their environment. It relates to the functioning of the body and is not visibly apparent like morphological variation.

Examples of physiological Variation:

  1. Few people can roll their tongues.
  2. Every human possesses one of the four blood groups called A, B, AB and O. This is based on the cell factor called antigen.
  3. Disparities in ability to taste phenylthiocarbamide (PTC)

Application of Variation

The knowledge of variations in human population is applied in many ways. These include:

  1. Crime detection: Remember when I mentioned that fingerprints are unique to each person? Detectives use finger prints in identifying people suspected to have committed certain crimes. This is based on the assumption that no two persons possess exactly the same fingerprints and that human fingerprint remain the same throughout one’s life span. Hence, if the fingerprints of a suspect are exactly like those at the scene of a crime, the suspect might be held as being responsible for the crime. Fingerprints on dangerous weapons can also be investigated to detect criminals such as assassins using riffles.
  2. Blood groups: Every human being belongs to any of the four blood groups A, B, AB or O. The knowledge of human blood group is used as follows:
    • Blood transfusion: If the transferred blood does not match that of the recipient, the recipient’s blood will clump or agglutinate. Death can result from the agglutination. People in blood group O can donate blood to people in all other groups. Hence, they are called universal donors. People in blood group AB can receive blood from people in other groups. Thus they are called universal recipients.
    • Crime detection: When blood stains got from the scene of a crime is analysed, the result can be used by detectives to identify arrested suspects and hence detect the actual criminals.
    • Paternity: when there is a dispute as to the actual father of a baby, the knowledge of blood groups can be used to prove the paternity of the child. For example, if the baby’s blood falls under blood group AB and its mother is in blood group A, the baby's genotype will be IA IB and the mother IA; or IA IA, certainly, the IB gene of the baby must have been inherited from the father. Supposing the alleged father is in blood group O, it is not likely that the baby belongs to him. If he is real father, the baby would have blood type A.