Intraspecific variation - less obvious is the distinction between the two individuals of the same species but nevertheless there are small differences (thus no two elephants are found to be identical)
Cause of variation
- variation is the result of either genetic differences or the influence of the environment
- in many cases its a combination of both genetic and environmental factors
Genetic differences
- are due to different genes each individual possesses
- genetic variations arises as a result of
- mutations
- these sudden changes to genes and chromosomes may or may not be passed onto the next generations
- meiosis
- this special form of nuclear division forms the gametes - this mixes up the genetic material before it is passed on to the gametes all of which are therefore different.
- fusion of gametes
- in sexual reproduction the offspring inherit some characteristics of each parent and are therefore different from both of them
- which gametes fuses with which at fertilisation is a random process adding to the variety of the offspring.
Discontinuous variation
- Qualitative difference between phenotypes
- Some characteristics of organisms grade into one another; there are no separate categories but a complete range of values.
- examples
- ear lobe shapes
- ability to role tongue
- blood type
- gender
- due to
- influence of one or more genes
- if greater than one they behave epistatically
- if only one gene then its called monogenic
- different alleles at a single gene locus have large effects on the phenotype
- different gene loci have different effects on the phenotype
- e.g. codominance
Continuous variation
- due to
- more than one gene - polygenic
- genes provide an additive effect to the phenotype
- different alleles at a gene locus have a small effect
- genes found on different chromosomes
- environmental influences
- affect the way the organisms' genes are expressed.
- the genes set limits but its largely the environment that determines where within those limits the organism lies
- e.g.
- temperature
- rainfall
- soil conditions
- pH
- food availability
- Variation and selection
- variation and selection is necessary within population
- selection can be natural or artificial.
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