40 Fun Facts About Mitosis

Many chemotherapy drugs block mitosis in fast-dividing cells, causing which common side effect?

Hair loss follows because hair follicles hold some of the fastest-dividing cells in the body, so drugs aimed at dividing tumor cells hit them too. The gut lining suffers for the same reason.

Which human organ can regrow to full size by mitosis after surgeons remove a large part of it?

The liver is the only internal organ that can pull this off, which is why a living donor can give part of theirs away. Its cells normally sit idle and rarely divide.

Whose tumor cells, taken without her knowledge at Johns Hopkins, still divide in labs worldwide?

Henrietta Lacks died in 1951, but her cells became the first human cell line able to divide without limit. Known as HeLa, they were used to test the first polio vaccine.

Named for how chromosomes look under a microscope, 'mitosis' comes from the Greek word for what?

Thread is the meaning of the Greek 'mitos': stained chromosomes showed up as long strands at the start of division, two decades before anyone linked them to heredity.

What does mitosis, the division behind growth and tissue repair, produce from one parent cell?

Two identical cells result, each carrying the same DNA as the parent. That is why the fresh skin replacing what you shed every day is a perfect match for the old.

Which human cell type can never divide by mitosis because it ejects its nucleus as it matures?

Red blood cells give up their nucleus to make room for more oxygen-carrying hemoglobin, so bone marrow has to build replacements at a rate of over two million every second.

A human cell with 23 pairs of chromosomes divides by mitosis, giving each daughter cell how many?

46 is the full human set, and mitosis never changes the count. Only sperm and egg cells, made by a different kind of division, drop to 23.

Which type of cell division, unlike mitosis, halves the chromosome number to make sperm and eggs?

Meiosis divides twice in a row, leaving each sex cell with half the usual chromosomes, so that an egg and a sperm restore one full set when they join.

Which stage of mitosis, used by labs to photograph chromosomes, lines them up across the middle?

Metaphase is the moment every chromosome sits on the cell's equator, tugged equally toward both ends. Chromosomes are easiest to see then, so it is the stage used for medical chromosome tests.

Which unspecialized cell type in bone marrow keeps dividing by mitosis throughout a person's life?

Stem cells can renew themselves again and again while also producing specialized offspring, which is why a bone marrow transplant can rebuild a patient's immune system.

Which cell-cycle stage, once misnamed the 'resting phase', takes up most of a typical cell's life?

Interphase takes up about 90 percent of a cell's life, and it is anything but restful: the cell grows, does its everyday work and copies all of its DNA.

In which stage of mitosis do chromatids form V shapes as spindle fibers drag them to opposite poles?

Anaphase is the moment the sister chromatids finally let go of each other. Each is towed by a single attachment point, so its arms trail behind like streamers.

In which stage of mitosis do chromosomes first become visible as the nucleolus fades from view?

Prophase is when loose DNA coils into compact chromosomes that can be moved without tangling. Before then, even a good light microscope shows only a grainy nucleus.

In which stage of mitosis does a new membrane wrap each set of chromosomes as they begin to uncoil?

Telophase undoes the opening moves of mitosis: the chromosomes relax back into loose DNA, the spindle is dismantled and each new nucleus regains its nucleolus.

Which process, not counted as a stage of mitosis, divides the cytoplasm to complete cell division?

Cytokinesis usually overlaps the last moments of mitosis, but it can be skipped: some fungi and slime molds divide their nuclei again and again inside one giant cell.

Rigid walls cannot pinch inward after mitosis, so plants divide by building which structure instead?

A cell plate starts as a row of tiny sacs in the center and spreads outward until it meets the side walls, becoming the new wall between the daughter cells.

Which indentation, tightened like a drawstring, pinches an animal cell apart after mitosis?

The cleavage furrow deepens as a ring of protein contracts beneath it, driven by the same pair of proteins that power muscles, until the cell is squeezed apart at the waist.

Which pinched-in region of a chromosome holds its sister chromatids together during mitosis?

The centromere is the narrow waist that gives a duplicated chromosome its familiar X shape, and it is also where the spindle fibers get their grip.

Bacteria have no nucleus, so instead of mitosis they copy themselves by which simpler process?

Binary fission can be astonishingly quick: with no nucleus or spindle to organize, E. coli can double its numbers in as little as 20 minutes.

Mitosis builds a whole human body from which single cell, formed when a sperm meets an egg?

The zygote divides again and again by mitosis, and its descendants go on to specialize into the hundreds of kinds of cell in an adult body.

Which loose form of DNA, named from the Greek for 'color', fills the nucleus between cell divisions?

Chromatin earned its name by soaking up laboratory dyes so readily. Only when a cell gets ready to divide does it bundle up into separate, countable chromosomes.

Which German biologist coined the word 'mitosis' after staining dividing salamander cells?

Walther Flemming published his findings in 1882 but had never come across Mendel's work, so two decades passed before anyone grasped what his carefully shared-out chromosomes meant for heredity.

Which paired cylinders sit at an animal cell's spindle poles but are absent from flowering plants?

Centrioles help organize the spindle in animal cells, yet flowering plants and conifers carry out mitosis perfectly well with none at all, so they cannot be essential.

Which term names the number and look of a cell's chromosomes, as photographed in mid-mitosis?

A karyotype test lines the chromosomes up in matched pairs by size, letting doctors spot an extra or missing one, such as the third copy of chromosome 21 in Down syndrome.

Which structure breaks apart early in animal mitosis so spindle fibers can reach the chromosomes?

The nuclear envelope has to go because an animal cell's spindle forms outside the nucleus. Yeasts do it differently, keeping the nucleus sealed and building the spindle inside.

In which part of the cell cycle, before mitosis rather than during it, does a cell copy its DNA?

S phase stands for synthesis: every chromosome is duplicated just once, and the twin strands stay joined together until mitosis pulls them apart.

Which tiny freshwater relative of jellyfish clones itself by growing a bud through mitosis?

Hydra can sprout a new bud every two days when well fed, and because its cells are constantly renewed it shows no sign of growing old.

Which programmed cell death, from the Greek for 'falling off', removes cells whose mitosis fails?

Apoptosis is a tidy self-destruct routine, and a busy one: an adult body retires tens of billions of cells this way every day, with mitosis supplying the replacements.

Most animal cells, normally flat or stretched, pull themselves into which shape as mitosis begins?

A sphere gives the spindle room to assemble and capture every chromosome. Cells that are prevented from rounding up tend to build faulty spindles.

Which protective chromosome caps shorten with each division until a normal cell can divide no more?

Telomeres work like a countdown clock, allowing normal human cells roughly 40 to 60 divisions. Most cancer cells cheat by switching on an enzyme that rebuilds them.

Spindle fibers are built from which hollow protein rods, also used as cargo tracks inside a cell?

Microtubules grow and shrink constantly, and that restlessness is the point: during mitosis they shorten to reel the chromosomes toward the poles.

Which tree's bark gave medicine Taxol, a cancer drug that jams the spindle so mitosis cannot finish?

The Pacific yew dies when its bark is stripped, so the drug is now made from yew needles or cultured plant cells instead. It works by freezing spindle fibers in place.

Which protein structure, built on each chromatid during mitosis, do spindle fibers attach to?

The kinetochore doubles as a tension sensor: until every one reports a firm grip from both poles, the cell will not let the chromatids separate.

Which gout drug from the autumn crocus stops spindle fibers forming, stalling cells in mid-mitosis?

Colchicine is prized by plant breeders precisely because it derails division: treated cells can end up with extra chromosome sets, a trick behind seedless watermelons.

Which division-pacing proteins did Tim Hunt discover in sea urchin eggs, earning a Nobel Prize?

Cyclins build up and are then destroyed in every round of division, which is how Hunt noticed them: one protein kept vanishing each time the eggs divided.

Which gene's protein, nicknamed 'guardian of the genome', halts cell division when DNA is damaged?

TP53 is switched off in more than half of human cancers, which lets cells with broken DNA carry on dividing when they should have stopped.

Which bloodstream components bud off giant bone-marrow cells that keep copying DNA without dividing?

Platelets come from megakaryocytes, which start mitosis over and over but abandon it each time, ending up with as many as 64 sets of chromosomes in one swollen nucleus.

Which ring-shaped protein holds sister chromatids together in mitosis until an enzyme cuts it?

Cohesin is sliced by an enzyme aptly named separase, and the cut lands on every chromosome at almost the same instant, which is why the chromatids part in unison.

Which protein, also at work in muscle, forms the ring that pinches a dividing animal cell apart?

Actin filaments form a belt just under the cell membrane, and their motor partner myosin slides them together, the same pairing that makes a bicep contract.

Which term covers every body cell that divides by mitosis, unlike those that make sperm and eggs?

Somatic cells are a genetic dead end: a mutation in one can spread to its own descendants within the body but can never be passed on to a child.