How does a cell divide to produce two genetically identical cells for growth and repair?
Explain how mitosis and the cell cycle produce two genetically identical cells, describe its role in growth, repair and asexual reproduction, and explain how uncontrolled division leads to cancer (NYSSLS LS1 and LS3, stability and change; cause and effect).
A NYSSLS-level answer on mitosis for the New York Life Science: Biology Regents: the cell cycle, how mitosis produces two identical cells, its role in growth, repair and asexual reproduction, and what happens when division is not controlled.
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What this topic is asking
NYSSLS asks you to explain how cells divide to make genetically identical copies for growth and repair, and why this division must be controlled. On the Life Science: Biology Regents, mitosis is often contrasted with meiosis (the next topic), and clusters frequently ask about chromosome number or the consequences of division going wrong (cancer). The crosscutting concept is stability and change: mitosis keeps the genetic information stable across cell generations.
The cell cycle
The key point for the exam is the order: the cell grows and replicates its DNA first, then divides. Replicating the DNA beforehand is what allows each new cell to receive a complete copy (see DNA structure and replication).
What mitosis produces
This identity is the defining feature. Because the DNA was copied accurately and then shared equally, the daughter cells carry the same genes as the original. This contrasts sharply with meiosis, which halves the chromosome number and produces variation.
Why organisms need mitosis
Mitosis serves several roles in living things:
- Growth. A multicellular organism grows by increasing its number of cells.
- Repair and replacement. Damaged tissue is repaired, and worn-out cells (such as skin and blood cells) are continually replaced.
- Asexual reproduction. Single-celled organisms and some multicellular ones reproduce by mitosis, producing offspring genetically identical to the parent (clones).
In every case, producing identical cells is an advantage: the new cells have the same correct instructions as the originals.
When control fails: cancer
The cell cycle is normally regulated so that cells divide only when needed. If these controls fail (often through mutations in the genes that control division), cells may divide uncontrollably, forming a mass called a tumor. A malignant tumor is cancer. The extra cells serve no useful purpose and can crowd out and damage healthy tissue. This is a cause-and-effect link the exam tests: loss of regulation leads to uncontrolled division.
Try this
Q1. State two cells that result from mitosis in terms of their genetic content and chromosome number. [2]
- Cue. Two genetically identical cells, each with the same chromosome number as the original cell.
Q2. Explain why uncontrolled mitosis can be harmful. [2]
- Cue. Cells divide without control and form a tumor (cancer); the extra cells have no useful function and can damage normal tissues.
Exam-style practice questions
Practice questions written in the style of NYSED exam questions on this dot point, with worked answer explainers. The year tag is the paper they imitate, not the source.
Regents (Life Science sample, 2024)3 marksA body (skin) cell with 46 chromosomes divides by mitosis. (a) State the number of chromosomes in each new cell. (b) State whether the new cells are genetically identical to or different from the original cell. (c) Explain the role of DNA replication before mitosis in producing identical cells.Show worked answer →
A 3-point constructed-response item assessing patterns and stability and change.
(a) 1 point: 46 chromosomes (the same number as the original).
(b) 1 point: genetically identical (to each other and to the original cell).
(c) 1 point: DNA is replicated before mitosis so there are two copies of each chromosome; mitosis then separates them so each new cell receives a full, identical set, keeping the cells genetically the same.
Markers reward "46, identical" and linking replication to each cell getting a complete copy.
Regents (Life Science CR, 2025)2 marksCell division is normally tightly controlled. (a) State one normal role of mitosis in a multicellular organism. (b) Explain what can happen if the controls on cell division fail.Show worked answer →
A 2-point item on the role and regulation of mitosis.
(a) 1 point: any correct role, for example growth, repair of damaged tissue, or replacement of old cells (asexual reproduction in single-celled organisms is also acceptable).
(b) 1 point: if the controls fail, cells divide uncontrollably, which can form a tumor (cancer); the extra cells serve no useful function and can damage normal tissues.
Markers reward a correct role and "uncontrolled division forms a tumor/cancer".
Related dot points
- Describe the structure of DNA (the antiparallel double helix and base pairing) and explain how complementary base pairing allows DNA to be copied accurately during replication (NYSSLS LS3, structure and function; patterns).
A NYSSLS-level answer on DNA for the New York Life Science: Biology Regents: the double-helix structure, base pairing, why DNA is a stable store of information, and how complementary base pairing allows accurate replication.
- Explain how meiosis produces gametes with half the chromosome number and generates genetic variation through crossing over and independent assortment, and how fertilization restores the chromosome number (NYSSLS LS3, patterns; cause and effect).
A NYSSLS-level answer on meiosis for the New York Life Science: Biology Regents: how meiosis halves the chromosome number to make gametes, how crossing over and independent assortment create variation, and how fertilization restores the chromosome number.
- Explain how genes are expressed through transcription and translation, how the sequence of DNA bases codes for the sequence of amino acids in a protein, and why this links genotype to phenotype (NYSSLS LS3, structure and function; cause and effect).
A NYSSLS-level answer on protein synthesis for the New York Life Science: Biology Regents: how transcription makes mRNA from DNA, how translation reads codons to build a protein, and how the base sequence of a gene determines a protein and so a trait.
- Explain how mutations change the DNA sequence and their possible effects, and describe how genetic technologies such as selective breeding and genetic engineering are used (NYSSLS LS3, cause and effect; structure and function).
A NYSSLS-level answer on mutations and biotechnology for the New York Life Science: Biology Regents: what mutations are and their effects, how they create variation, and how selective breeding and genetic engineering are used and assessed.
- Explain how cells with the same DNA become specialized through differential gene expression, and describe the role of stem cells in development and repair (NYSSLS LS1, structure and function; cause and effect).
A NYSSLS-level answer on differentiation for the New York Life Science: Biology Regents: how cells with identical DNA specialize by expressing different genes, what stem cells are, and how this builds and maintains a multicellular body.
Sources & how we know this
- New York State P-12 Science Learning Standards (Life Science) — New York State Education Department (2016)
- Educator Guide to the Regents Examination in Life Science: Biology — New York State Education Department (2025)