Answer: Genetic variation can be caused by mutation (which can create entirely new alleles in a population), random mating, random fertilization, and recombination between homologous chromosomes during meiosis (which reshuffles alleles within an organism's offspring).
By the end of meiosis, the resulting reproductive cells, or gametes, each have 23 genetically unique chromosomes. The overall process of meiosis produces four daughter cells from one single parent cell.
Explanation:
During meiosis, homologous chromosomes (1 from each parent) pair along their lengths. The chromosomes cross over at points called chiasma. At each chiasma, the chromosomes break and rejoin, trading some of their genes. This recombination results in genetic variation.
"In the early days of germ theory, contagious diseases
were thought to be caused by fungi or bacteria. In the 1890's, Dmitri
Ivanovski filtered extracts from diseased tobacco plants and discovered
that the disease could be transmitted to new plants through the
filtrate. He concluded that the disease was caused by particles smaller
than bacteria; the tobacco mosaic virus", is partially correct. Dmitri
Ivanovski discovered that filtered extracts from diseased tobacco plants
could be transmitted to new plants through the filtrate. However, it
was Dutch microbiologist Martinus Beijerinck who, while replicating
Ivanovsky's experiments, proved that the filtrate contained a new
infectious agent. Beijerinck named this agent a virus.
one is adapted to live in a hot and dry environment and one is adapted to live in a humid environment.
They are further classified into: fish, amphibians, birds, reptiles and mammals.
I hope I've helped : )
