A phenotype/trait may be influence and determined by more than one gene in cumulative way.
features:
The gene individually has little effect but addictive effect is significant.
The multiple gene may or may not be on the same homologous chromosome
It is responsible for the inheritance of quantitative traits.
difficulty in distinguishment of ploygenic inheritance:
Many of the polygenic character is strongly influenced by environmental factors.
Types of variation
Discontinuous variation
- distinct phenotype -->organism place in definite catagory
- qualitiative = cannot be measure
- character controlled by single gene --> not affect by enviroment
Continuous variation
- gradual transition between two extreme
- quantitative = can be measure
- combined effect of polygene and enviroment
- exhibit normal distribution curve
Source of biological variation
A. Reshuffling of gene/gene recombination
- random fusion of gamete during fertilization
- crossing over between homologous chromosome
- independent assortment of homologous chromosome
Mutation
Definition:
A sudden change in amount or structure of genetic material in chromosome which involve change in phenotype.(?)
Occurrence:
Spontaneous mutation-->error in replication, gene mutate itself randomly
Induced mutation-->x-ray, mutagenic chemical e.g. mustard gas
Types of mutation:
1. Change in structure
Deletion: a portion of chromosome is lost
Duplication: a portion of base sequence is duplicated
Inversion:...... is inverted
Translocation: a part of a chromosome breaks off and
---------------join another part of non-homologous chromosome
IDDT
Consequence:
Any change or rearrangement of the sequence will produce wrong sequence of amino acid
--> protein --> enzyme,since enzyme is important in controlling metabolic activities-->Alternation is usually harmful.
2. Change in chromosome number
Usually during meiosis.
One pair of chromosomes fail to separate at anaphase, resulting one gamete in extra and one in missing. This is called non-disjunction.
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