Answer:
all of these options are correct.
Explanation:
There is a research paper published in 2012 which support option i.
i. Chance, a mistake by cellular machinery, or damage from an environmental agent can cause gene mutation.
Reference: Chan, Kin, et al. "Base damage within single-strand DNA underlies in vivo hypermutability induced by a ubiquitous environmental agent." PLoS genetics 8.12 (2012).
There is a research paper published in 1969 which support option ii. According to this paper chromosome exchange is called crossing over which is the reason of variation in offspring.
ii.Before the pairs separate, pieces of the two chromosomes in each pair are exchanged.
Reference: Wagenaar, E. B. "End-to-end chromosome attachments in mitotic interphase and their possible significance to meiotic chromosome pairing." Chromosoma 26.4 (1969): 410-426.
There is a research paper published in 1984 which support option iii. According to this paper chromosome follow law of independent assortment which results in variation in genetic make of daughter cell.
iii. It is a matter of chance as to which chromosome on a pair goes to the gamete.
Reference: Monaghan, Floyd, and Alain Corcos. "On the origins of the Mendelian laws." Journal of Heredity 75.1 (1984): 67-69.
