Variation
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  • 1. LEARNING OBJECTIVES: 1. Understanding variation in organisms 2. Understanding the causes of variation 3. Being respectful towards one another despite variation VARIATION The difference between organisms of the same species.
  • 2. Continouos variation is the variation that have range of values from the smallest o the biggest . Eg. shortest – tallest lightest - heaviest Discontinuous variation – which have no range: you either have the characteristic ,or you do not OR you can do something or you cannot.
  • 3. Examples of continuous variation Exapmles of discontinuous variation
  • 4. CAUSES OF VARIATION GENETIC FACTORS ENVIRONMENTAL FACTORS Crossing -over Independent assortment mutations Random fertilisation Nutrition temperature light intensity
  • 5. CAUSES OF VARIATION Environmental
  • 6. GENE MUTATION – (point mutation) occurs at a single locus or gene position on a chromosomes - Sickle – cell anaemia - Albinism - Hutchinson –Gilford Progeria syndrome ( rapidly ageing ) -Polydactylism CHROMOSOMAL MUTATION : 1. Increase or decrease in the number of chromosomes -Down’s syndrome (47 hromosomes) -Turner’s syndrome (45 chromosomes) -Triploid (3n) -Tetraploid (4n) Polyploidy – is common among flowering plants and food plants like apples ,tomato and wheat polyploidy 2. A change in the structure of the chromosomes – rearrangement of whole blocks of gene son a chromosomes.
  • 7. The importance of variation in the survival of a species. The moth exists in two forms ,grey and dark melanic. The grey Biston well carmouflaged against lichen – covered tree trunks In unpolluted enviroments, giving them protection from predators. However, in such unpolluted environments , dark melanic Biston are not carmouflaged and their numbers decrease drastically due to predation. In 1940s ,the onset of Industrial Revolution in England, air quality declined and soot was deposited on tree trunk , killing lichen and the grey moths were not carmouflaged the melanic moths became dominant until 1960s when the Clean Air Act was introduced in the cities. After that the quality improved and the number of melanic moths decreased.