a. Mutations
Mutations are ultimate sources of variations in most populations. Mutations are heritable changes in the genetic constitution of an organism. It may involve changes of a gene from one form to another.
Typical values of mutations are about 10^5 per gene or less. So the impact of mutation in any one generation is small. Since all morphological and physiological character of an organism is controlled by genetic information derived by the DNA, any mutation changes in their characters are due to some change in DNA. There are four basic types of change in DNA.
b. Gene recombination
Genetic recombination is the production of offspring with combinations of traits that differ from those found in either parent. In eukaryotes, genetic recombination during meiosis can lead to a novel set of genetic information that can be passed on from the parents to the offspring.
c. Migration
This is the movement of genes through pollen, seeds or transplanting of trees. Although mutation and migration are different processes, they resemble each other in one aspect; both are ways in which new genes can be introduced into a population. The difference is that mutation rates are low while migration rates are high.
In migration the movement of genes into a population is only considered. Pollen and seeds are nearly always produced in such excess that the removal from the stand does not affect the genetic information in the stand.
d. Ploidy levels
The number of chromosome sets a tree has is termed ploidy. It can greatly affect the variability pattern within and among species. Usually each parent contributes one set (1n) of chromosomes for a progeny so that a tree has 2 sets of chromosomes and it is called a diploid (2n) set.
Dullayo answered the question on August 14, 2018 at 05:27
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