Inheritance and Genetics: Question 6
Syllabus 17.2
A species of aquarium fish has 24 chromosomes in each body (somatic) cell, arranged as 12 homologous pairs. A skin cell from an injured fin divides by mitosis to replace damaged tissue as the fin heals.
Which statement correctly describes the daughter cells produced by this mitotic division?
Show worked solution Hide worked solution
Worked solution
Step 1: Recall what mitosis does
Mitosis is the type of nuclear division used for growth and the repair of damaged tissue. It produces new cells that are genetically identical to the parent cell, and it does not change the chromosome number: a cell that starts as diploid (with chromosomes in pairs) produces diploid daughter cells with the same number of chromosomes.
Step 2: Apply this to the fish skin cell
The parent skin cell has 24 chromosomes (12 pairs). Mitosis involves one division of the nucleus, copying the chromosomes first so that each daughter cell receives a complete, identical set. This gives two daughter cells, each with the full 24 chromosomes, and each genetically identical to the parent cell (and to each other), since no new genetic combinations are created.
Why the other options are wrong
- B: this halves the chromosome number to 12, which is what happens in meiosis, not mitosis. Mitosis keeps the chromosome number the same as the parent cell.
- C: this describes meiosis (four daughter cells, a halved chromosome number, and genetic variation between them) none of which apply to mitosis.
- D: this keeps the correct chromosome number (24) but wrongly claims the daughter cells are genetically different. Mitosis produces genetically identical cells; it is meiosis that produces genetic variation.
Final answer
Mitosis produces two daughter cells, each with the same chromosome number as the parent cell (24) and genetically identical to it, option A.