Haploid
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Haploid describes a cell or organism that has a single set of chromosomes, such as a human egg or sperm cell with 23 chromosomes.
Also: haploidy
Definition
What does haploid mean?
A haploid cell carries one set of chromosomes, so each kind of chromosome is present only once. Geneticists write this number as n. In humans n is 23, and the only haploid cells are the gametes, eggs and sperm, which form by meiosis from diploid cells with 46 chromosomes (2n). When an egg and a sperm fuse at fertilization, the zygote regains two sets. Halving the number in meiosis and doubling it at fertilization keeps the chromosome count steady across generations.
Because a haploid cell has just one copy of each gene, any recessive allele it carries is expressed, with no second copy to hide it. This makes haploid organisms useful in genetics research. Baker's yeast, Saccharomyces cerevisiae, can grow as either haploid or diploid cells, so mutations are easy to detect in its haploid form.
Many organisms spend much of their lives haploid. Most fungi and many algae have a haploid body, and their zygote, the only diploid cell, quickly undergoes meiosis. Plants alternate between a haploid gametophyte and a diploid sporophyte. In bees, wasps and ants, males usually hatch from eggs that were never fertilized and so are haploid, whereas females are diploid.
Word parts
Where does the word “haploid” come from?
- haplo-
- single, simpleGreek haploos
- -oid
- like, having the form ofGreek eidos (form)
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Terms that go with it
- DiploidDiploid describes a cell or organism with two complete sets of chromosomes, one inherited from each parent, as in most human body cells.
- MeiosisMeiosis is a two-stage cell division that turns one diploid cell into four genetically different haploid cells, the precursors of eggs and sperm.
- GameteA gamete is a haploid reproductive cell, such as a sperm or an egg, that fuses with a gamete of the opposite type at fertilization to form a zygote.
- ChromosomeA chromosome is a thread-like structure of DNA and protein that carries an organism's genes; most human cells hold 46 of them in 23 pairs.
- Alternation of generationsAlternation of generations is a life cycle in which a multicellular haploid gametophyte and a multicellular diploid sporophyte produce each other in turn.
- EusocialityEusociality is the most complex form of animal social life, in which colony members share brood care and only a few reproduce while the rest work.
Sources
Checked against
Written for biofideX in plain words, after checking these references:
- NHGRI Talking Glossary: Haploid
- OpenStax Biology 2e, 11.1 The Process of Meiosis
- OpenStax Biology 2e, 11.2 Sexual Reproduction
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