SS3 Second Term Biology Lesson Note – Variation in Population

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WEEK 3

VARIATION IN POPULATION

Variation can be defined as the differences that occur between individual or organisms of the same species. Variation is caused majorly by

1. Genetic of differences or genotypic variation
2. Effect of environmental factor.

The genetic differences or genotypic variation may be as a result of new genetic combination which occur during sexual reproduction or due to mutation, a rare and spontaneous alteration that occur in genes or chromosome. This type of variation is inheritable and can be transferred from parent to offspring. For examples variations in eye colour and disease resistance.

Variation due to effect of environmental factors such climate, food supply and action of other organism on the expression of the genetic potential. Such variations are not heritable but acquired and cannot be transferred from parent to offspring.

TYPES OF VARIATION

Morphological or continuous variation

Morphological variation are variations that deal with physical appearance of individual or an organism. It concerns form and structure or an organism or a plant. It helps us to identify and differentiate individual in population based on their physical appearance.

Continuous variation is a type of variation in which a particular feature shows a smooth gradual transition between two extremes with the majority of individuals at the centre. For example, a graduation in height from short to tall is a continuous variation since there are intermediate forms as majority of individuals are of average height.

Example of continuous or morphological variation in human being are

1. Height of the body
2. shape of the body parts e.g. head, jaw, mouth, nose
3. Size of various part of the body such as head, nose ear, eye, hand and lips.
4. Colour of part other body such as skin, hair, and the eye.
5. Finger print

Physiological or discontinuous variation.

Physiological variation are variations which are related to the functioning of the body. It is a discontinuous type of variation since it composed of well-defined classes with no intermediate forms. For example, the blood group composed of four distinct classes A, B, AB and O, which indicate sharp differences between the various blood groups. No intermediate feature of a particular trait.

Examples of discontinuous variation or physiological variation in human being are

1. Rolling of tongue
2. Moving the ears without moving the head
3. Closing one eye and leaving the other open
4. Tasting the chemical substance called phenylthiocarbamide (PTC). some people can taste the chemical while others cannot
5. Differences in blood group A, B, AB and O in man. Each person belongs to one of these group.
6. Sex of an individual. An individual will either belong to a male or female
7. Behavioural pattern of an individual can be grouped as being excitable or calm, pessimistic or optimistic, mean or Kind, gentle or harsh, timid or brave, intelligent or foolish. Environmental factors and genetic make-up of individual are believed to contribute greatly to their behaviour.

APPLICATION OF VARIATION

It can be used to trace or detect the perpetuator of crime by using finger printing.

Explanation: Forensic examination of objects or substance seen at the scene of crime may provide necessary clue of the suspect. Finger printing is a technique used in forensic examination based on the impression of the finger tips left on surface touched bare-handed. Dusting the surface with powder using a brush allows the powder to stick to the protein secreted by the sweat glands on the skin ridges of the finger tips. Upon the removal of excess powder, an outline the contours of the rigdes remain. Another method is chemical treatment to reveal contours. The finger print of potential suspects compared with the one under examination. Any individual whose finger print matches the finger print on the gun or other material picked from the scene of the crime will be taken as an accused person.

(b) DNA Finger printing is used in identifying a rapist. The body cell or DNA sample is first extracted from body tissues or fluid at the scene of the crime and fragment using enzyme. The DNA pattern is analyzed to defect the criminal.

Finger prints

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