Which of the following is not a source of genetic variation?
a) random fertilization of eggs by sperm
b) independent assortment of chromosomes
c) crossover of homologous chromosomes
d) age of either or both parents

The correct answer is option d) age of either or both parents.

Explanation:

Genetic variation is the difference in nucleotide sequences between individuals organisms within a particular population. Variation can occur either in germ cells that are sperm and egg or in somatic cells or in both.

Random fertilization of egg and sperm can lead to genetic variation is every germ cell has a different set of chromosomes. Independent assortment of chromosomes is also the same as random fertilization as it is also random. Crossing over of homologous chromosomes is one of a major source of the genetic variation as it forms a new set of chromosomes.

Thus, the correct answer is option D) age of either or both parents.

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answer : haversian

[explanation: -(compact bone is organized as parallel columns, known as haversian systems, which run lengthwise down the axis of long bones. these columns are composed of lamellae, concentric rings of bone, surrounding a central channel, or haversian canal, that contains the nerves, blood vessels, and lymphatic system of the bone)]