variation

LEARNING OBJECTIVES:

1. Understanding variation in organisms2. Understanding the causes of variation3. Being respectful towards one another despite variation

VARIATION

The difference between organisms of the same species.

Continouos variation is the variationthat have range of values from thesmallest 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 somethingor you cannot.

Examples of continuous variation

Exapmles of discontinuousvariation

CAUSES OF VARIATION

GENETIC FACTORS ENVIRONMENTAL FACTORS

Crossing -over

Independent assortment

mutations

Random fertilisation

Nutrition temperature light intensity

CAUSES OF VARIATION

Environmental

GENE MUTATION – (point mutation) occurs at a single locus or geneposition 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.

The importance of variation in the survival of a species.

The moth exists in two forms ,greyand dark melanic.The grey Biston well carmouflagedagainst lichen – covered tree trunksIn unpolluted enviroments, giving them protection from predators.However, in such unpolluted environments , dark melanic Biston arenot carmouflaged and their numbersdecrease drastically due topredation. In 1940s ,the onset of Industrial Revolutionin England, air quality declined and soot was deposited on tree trunk , killing lichenand the grey moths were not carmouflagedthe melanic moths became dominantuntil 1960s when the Clean Air Act wasintroduced in the cities. After that the quality improved and the number ofmelanic moths decreased.