If an organism's diploid chromosome number is 18, how many different possible combinations of homologous chromosomes lining up during meiosis exist for the eggs or sperm produced by that organism?

a. 128

b. 18

c. 36

d. 9

e. 512

D. 9

Notice that diploid cells which 18 are the complete number of chromosome pair of the organism. This usually happens under cell divison - mitosis which process of replicating oneself to produce another like cell. Meiosis occurs in gametes, sex cells. Their respectively called spermatogenesis (sperm cells) and oogenesis (egg cells). These cell division - meiosis produces haploid cells, in which in words "half" from the complete cell chromosome number, hence, these haploid cells only produce half number or one set of chromosome (9) instead of the complete pair which in this case, 18.