Track DNA copying and chromosome numbers through ordinary cell division.
Method and worked examples
Before division, a cell copies its hereditary material. In binary fission, a prokaryotic chromosome is copied, copies separate as the cell grows, and the cell divides. Mitosis separates duplicated eukaryotic chromosomes into two nuclei; cytokinesis divides the cytoplasm. Under ordinary conditions both processes produce daughter cells with the same genetic information as the parent, apart from new mutations.
Diploid means two chromosome sets; haploid means one. Mitosis preserves the starting number of chromosome sets rather than halving it. DNA replication doubles DNA quantity before mitosis, but joined sister chromatids are counted as one duplicated chromosome until they separate. Growth and tissue repair commonly use mitotic division; gamete production involves meiosis instead.
Example 1
A diploid body cell with 12 chromosomes undergoes mitosis and cytokinesis. How many chromosomes are in each daughter cell?
Each daughter has 12 chromosomes. Mitosis preserves chromosome number.
Example 2
A culture begins with 5 cells and undergoes three complete binary-fission rounds with no deaths. Find the final number.
Each round doubles the population: 5×23=40 cells.
Watch out:Mitosis normally preserves chromosome number. Reduction to haploid sets is associated with meiosis.
Binary fission and mitotic division | Year 11 Biology | Ascent Arcade