crossing overPaired chromosomes trading matching segments. The chromosomes that come out of it carry combinations of gene forms that neither of them had before.
diploidHolding a matched pair of every chromosome. A diploid cell has its chromosomes twice over, one full set from each parent. Most cells of the human body are diploid.
egg cellThe gamete of the female parent, the larger kind. It cannot move by itself. In humans it is about 100,000 times as large in volume as a sperm cell.
fertilizationThe meeting and merging of an egg and a sperm. It brings two single sets of chromosomes together, so the number that meiosis halved is whole again.
gameteA reproductive cell that must merge with another. The egg cells and sperm cells of animals are gametes. The name was introduced in 1878 by the German scientist Eduard Strasburger.
haploidWith one chromosome of each kind, not a pair. A haploid cell has one set of chromosomes only. In bees, wasps and ants the males hatch from eggs that were never fertilized, so they are haploid.
Show all 36 terms (30 more)
Gametes, continued
homologous pairTwo chromosomes with the same genes, one per parent. The two may carry different forms of those genes. In mitosis they do not ordinarily pair up; in meiosis they do.
meiosisOne cell dividing twice to give four haploid cells. The DNA is copied once, before the first division, and not again before the second.
sister chromatidsBoth halves of one copied chromosome, still joined. They are identical copies, joined at the centromere. They stay together through the first division and part in the second.
sperm cellThe gamete of the male parent, the smaller kind. The sperm cells of animals can swim. Those of flowering plants cannot, and travel inside pollen.
tetradThe four chromatids of two paired chromosomes. Its other name is a bivalent. Bivalent counts the two chromosomes, and tetrad counts their four chromatids.
zygoteA fertilized egg cell, before it first divides. It carries everything needed to build a new individual, with half of the genetic information from each gamete.
Two divisions 12
anaphase IThe stage that parts the two chromosomes of a pair. Each chromosome travels whole to its end of the cell, with its two chromatids still joined.
anaphase IIThe stage in which a chromosome's two halves part. From the moment they part, each chromatid is called a chromosome.
chiasmaA visible link left where crossing over took place. The plural is chiasmata. They hold a pair of chromosomes together until anaphase I. Frans Alfons Janssens, a professor in Belgium, described them in 1909.
interkinesisA pause between the two divisions of meiosis. No DNA is copied during it. Many plants skip it and go straight on to prophase II.
meiosis IThe division that separates homologous chromosomes. It is called the reduction division, because each of the two cells it makes has half the chromosome number.
meiosis IIThe division that separates sister chromatids. It works much as mitosis does, and it turns the two cells of the first division into four.
metaphase IThe stage when chromosome pairs line up mid-cell. Which way round each pair faces is random, and no pair is steered by the others.
metaphase IIThe stage with unpaired chromosomes at mid-cell. The line they form is at a right angle to the line of metaphase I.
prophase IThe longest stage: matching chromosomes pair up. In mice it lasts 13 of the 14 days that meiosis takes. Crossing over happens during it.
synapsisThe zipping together of two matching chromosomes. A protein structure, the synaptonemal complex, forms between the two as they pair.
telophase IThe closing stage of the first division. The chromosomes arrive at the two ends of the cell. Each new cell has half the number, and every chromosome is still a pair of chromatids.
telophase IIThe closing stage of the second division. Nuclear envelopes form again, and the result is four cells with one haploid set each.
Life cycles 12
alternation of generationsA plant life cycle of haploid and diploid phases. The diploid phase makes spores by meiosis. The haploid phase that grows from a spore makes gametes by mitosis. All land plants live this way.
genetic recombinationThe making of gene combinations no parent had. Another name for it is genetic reshuffling. In meiosis it comes about in two ways: crossing over and independent assortment.
genetic variationHow individuals differ from one another in their DNA. The new combinations of DNA made in meiosis are one main source of it. Mutation is another.
germ cellA cell from which gametes are later made. The germ cells of many animals travel to the gonads while the embryo is forming. Every other cell of the body is called a somatic cell.
independent assortmentEach chromosome pair sorting by chance, on its own. Because of it, genes for different traits can be passed on independently of each other, as Gregor Mendel found with his pea plants.
nondisjunctionChromosomes failing to separate as they should. It can happen in either division, and it leaves cells with the wrong number of chromosomes. It was discovered in fruit flies in 1910.
oogenesisThe making of egg cells. In female animals, typically only one of the four cells that meiosis yields becomes an egg cell.
ploidyThe number of chromosome sets in a cell. A cell with three or more sets is polyploid. The strawberry sold in grocery stores has eight sets.
polar bodyA small cell cast off as an egg cell forms. The divisions that make an egg are uneven: most of the cytoplasm goes to the egg, and a polar body gets very little.
sexual reproductionReproduction that mixes the genes of two parents. Among animals, plants and fungi it is the commonest life cycle. Bacteria do not reproduce this way.
spermatogenesisThe making of sperm cells. One cell that enters meiosis yields four sperm cells.
sporeA reproductive cell that plants and fungi release. Spores are adapted for spreading and for surviving bad conditions, often for a long time.
How this list was compiled: Term list chosen for this site on 2026-10-15. Each meaning is written in our own words and was checked that day against the English Wikipedia (https://en.wikipedia.org/), whose text is under the Creative Commons Attribution-ShareAlike license: the articles Meiosis (the two divisions, their eight stages, tetrads, the reduction division, the 13 of 14 days in mice, the right angle of metaphase II, meiosis in plants and animals, and its history), Gamete, Ploidy, Chromosomal crossover, Bivalent (genetics), Zygote, Fertilisation, Egg cell, Sperm, Sister chromatids, Synapsis, Synaptonemal complex, Chiasma (genetics), Interkinesis, Mendelian inheritance, Genetic recombination, Nondisjunction, Polar body, Oogenesis, Spermatogenesis, Germ cell, Spore, Alternation of generations and Sexual reproduction. Checked a second time against the Talking Glossary of Genomic and Genetic Terms of the U.S. National Human Genome Research Institute (https://www.genome.gov/genetics-glossary), entries Meiosis, Gamete, Haploid, Diploid, Crossing Over, Homologous Recombination, Germ Line, Chromatid, Mendelian Inheritance and Genetic Variation (which the glossary titles Genomic Variation): two rounds of division and four haploid cells, 23 and 46 chromosomes in humans, the haploid males of bees, wasps and ants, paired chromosomes with the same genes in different forms, germ cells and somatic cells, and the strawberry with eight sets. Tetrad, synapsis, chiasma, interkinesis, zygote, nondisjunction, polar body, oogenesis, spermatogenesis, ploidy, spore, recombination, reduction division and sexual reproduction were also read in Wiktionary, the free dictionary (https://en.wiktionary.org/). The fact after each meaning is from the same pages. Licence: own work
How it works
This meiosis vocabulary worksheet sets meiosis, gamete, haploid, diploid, homologous pair, crossing over, tetrad, zygote and four more terms in one column and their meanings, shuffled, in the other. Its key prints as page 2.
Read the full guide
The two divisions, stage by stage
Set opens on Gametes. Two divisions has meiosis I, meiosis II, prophase I, metaphase I, anaphase I, telophase I, metaphase II, anaphase II, telophase II, interkinesis, synapsis and chiasma.
Variation and life cycles
The third list, Life cycles, has independent assortment, genetic recombination, genetic variation, nondisjunction, polar body, oogenesis, spermatogenesis, germ cell, spore, alternation of generations, ploidy and sexual reproduction.
Mitosis, cytokinesis, spindle and centromere are terms on the cell division vocabulary worksheet.
Questions and answers
What is the purpose of meiosis?
It makes reproductive cells that carry half the chromosomes of a body cell, so that when two of them join, the offspring has the full number and not double. It also deals the parents' genes out in new combinations.
Where does meiosis occur?
In every animal, plant and fungus that reproduces sexually. In animals it makes the gametes directly: egg cells in the ovaries, sperm cells in the testes. In land plants it makes spores, and the gametes come a generation later, by mitosis.
What is the difference between a gamete and a zygote?
A gamete, an egg or a sperm, is a cell with one set of chromosomes. A zygote is the cell that two gametes make by joining, with two sets. In humans a gamete has 23 chromosomes and a zygote 46.
Who discovered meiosis?
The German biologist Oscar Hertwig first described it in 1876, in the eggs of sea urchins. Edouard Van Beneden saw it again in 1883 in roundworm eggs, this time following the chromosomes. The name dates from 1905.