Back to Course

SS3: BIOLOGY - 2ND TERM

0% Complete
0/0 Steps
  1. Reproductive Behaviours | Week 1
    1 Topic
    |
    1 Quiz
  2. Life Cycles of Insects, Toads | Week 2
    6 Topics
    |
    1 Quiz
  3. Social Insects | Week 3
    2 Topics
    |
    1 Quiz
  4. Biology of Heredity (Genetics) I | Week 4
    4 Topics
  5. Biology of Heredity (Genetics) II | Week 5
    6 Topics
    |
    1 Quiz
  6. Biology of Heredity (Genetics) III | Week 6
    7 Topics
    |
    1 Quiz
  7. Variation | Week 7
    1 Topic
    |
    1 Quiz
  8. Evolution | Week 8
    3 Topics
    |
    1 Quiz
  • excellence
  • Follow

Lesson Progress
0% Complete

Topic Content:

  • Meaning of Variation
  • Types of Variation

In a population, differences exist between parents and offspring and among offspring.

Variation refers to the physical observable differences within a species.

The variations could be in the form of size, eye colour, coat colour, height, etc. Variations that are inherited, are determined by genes (genetic variations). Phenotypic variations may be brought about by genes, but can also be caused by the environment or a combination of both genes and the environment.

Some variations cannot be inherited because they are determined by certain factors in the environment.

Types of Variation:

There are two types of variations; morphological variations and physiological variations.

1. Morphological Variations:

Variations which relate to physical traits or outward appearance in organisms are known as morphological variations.

Examples include:

i) Weight

ii) Size of various parts of the body

iii) Colour of parts of the body examples are eye colour, hair or coat colour, 

iv) Facial features such as the shape of the jaw, mouth, nose, head etc

v) Fingerprints

2. Physiological Variations:

Variations which relate to the bodily functions of organisms are known as physiological variations.

Examples include:

i) Ability to taste a chemical, phenylthiocarbamide: This organic compound can taste bitter to some people but not to others.

ii) Ability to roll the tongue: Some human beings have the ability to roll their tongues while others cannot.

iii). ABO blood group system: There are four different blood groups in humans. A person can belong to only one blood group. The blood groups are A, B, AB, and O.

iv)  Behaviour: The personalities and behaviour of people differ. Even identical twins do not behave the exact same way.

Continuous Variations:

Continuous variations are variations within a population in which phenotypes may have any value between the extremes. Traits in the population tend to be quantitative. It is usually controlled by a lot of genes and strongly influenced by the environment.  

Intermediates exist within the population. Examples of such phenotypic traits are height, weight, and intelligence. If you measure the height of students in a class, you can group the students according to their height. A graph can be plotted to show the relationship between the number of students and their height. The graph shows a normal curve.

Screen Shot 2021 04 01 at 11.43.29 AM Easy Resize.com
Graph showing no of students in a class and their heights.

               

Discontinuous Variation:

In discontinuous variation, the variations appear as distinct, alternative characteristics with no intermediate forms among individuals in a population. It is controlled by a few genes and is usually unaffected by the environment. It tends to be qualitative.

Examples include tongue rolling, fingerprints, eye colour and blood groups.

Graph of tongue rollers and non-rollers
Graph of tongue rollers and non-rollers.
avatar