IMO Practice Test — Cell Cycle and Cell Division
6 Questions • 15 min • Olympiad level
15:00
Question 1 of 6
If a cell has 16 chromosomes before the S phase, how many will it have at the end of the S phase?
8
16 (but each with two chromatids)
32
4
Explanation: S phase doubles the DNA, not the chromosome number — 16 chromosomes, each now with two sister chromatids.
Question 2 of 6
A cell with 24 chromosomes undergoes mitosis. Each daughter cell will have:
12 chromosomes
24 chromosomes
48 chromosomes
6 chromosomes
Explanation: Mitosis is equational, so each daughter cell keeps 24 chromosomes.
Question 3 of 6
A cell with 24 chromosomes undergoes meiosis. Each of the four daughter cells will have:
24
12
48
6
Explanation: Meiosis halves the number, so each haploid cell gets 12 chromosomes.
Question 4 of 6
Crossing over increases variation because it:
Produces new combinations of parental genes
Doubles the DNA
Removes all genes
Stops the cell cycle
Explanation: Exchanging segments between homologues creates new gene combinations — the basis of recombination.
Question 5 of 6
Why is meiosis II often compared to mitosis?
Sister chromatids separate, with no further reduction in number
Homologous chromosomes pair
DNA is copied again
Four cells fuse
Explanation: In meiosis II the sister chromatids separate (as in mitosis); the reduction already happened in meiosis I.
Question 6 of 6
If gametes were formed by mitosis instead of meiosis, over generations the chromosome number would:
Stay the same
Keep doubling each generation
Become zero
Halve each generation
Explanation: Diploid gametes fusing would double the number every generation; meiosis prevents this by making haploid gametes.