One source of trait variations among individuals is the process of fertilization, in which when new ...

Answer to q. 1

Genetic mutations are the main source of generating new alleles, which lead to new traits. Mutations are constantly occurring within a population.

Other sources of variation include two events that occur during meiosis. Crossing over between homologous chromosomes produces new combinations of alleles and independent assortment of homologous chromosomes produces new combinations of chromosomes. Both of these events lead to the production of gametes with a lot of variation in traits.

Finally, variation can also arise from the change in chromosome number or structure.

Answer to q. 2

Microevolution refers to allele frequency changes within a population or species. For example, when natural selection works to change traits within a population, such as changes in beak sizes of a bird population or changes in antibiotic resistance in a bacterial population.

Macroevolution however, refers to large scale evolutionary events such as the diversification of several new species or the mass extinction of a whole species. It does not examine specific traits (alleles); instead, it looks at big picture events.