Haploid: Definition, Types, and Examples

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Haploid Definition

A state, a cell, or an organism that contains half of the normal full set of chromosomes in somatic cells is referred to as haploid in biology. This condition is referred to as haploidy. It’s only one of many different forms of ploidy. Other terms include monoploid (one set), diploid (two sets), and polyploid (three or more sets), comprising triploid (three sets), tetraploid (four sets), and so on.

What is Haploid?

The term haploid refers to a state, cell, or organism that has half of the homologous chromosomes found in a somatic cell. If two chromosomes have the same gene sequence, loci, chromosomal length, and centromere position, they are homologous.

The maternal half of the homologous pairings comes from the mother, while the paternal half comes from the father (coming from the father). A haploid cell, in other words, is one that possesses half of the total homologous chromosomes, or a single unpaired set of chromosomes.

Haploid Etymology

The word haploid comes from the Greek word haplous, which means “single.” The terms haploidic and haploidy are derived from each other. Their meanings depend on what haploid means. The term haploidic, for example, refers to a cell or organism with half of the set of homologous chromosomes.

When haploid is used as an adjective, haploidic can be used as a synonym for haploid. The term haploid refers to a haploid cell (e.g. germ cell) or organism (e.g. fungus) as a noun. Haploidy is a noun as well as a verb. It refers to a state that is defined by being haploid.

Haploid vs vs Other Ploidies

The number of sets of homologous chromosomes in a cell’s or organism’s genome is referred to as ploidy. The number n is assigned to each set. The condition of possessing half of a pair of chromosomes is referred to as haploidy.

The sign n is given to haploid cells (e.g. gametes) to denote that they only contain half of the chromosomal set of a somatic cell, which is any of the cells in a multicellular organism’s body except germ cells and sex cells.

Somatic cells in humans have two sets of chromosomes. As a result, a human somatic cell is a diploid cell and is denoted by the symbol (2n). The words haploid and monoploid are sometimes used interchangeably.

This is when haploid is defined as having a single copy of the chromosomes in a cell rather than half of a pair; monoploid is defined similarly. Polyploid refers to a situation in which a cell contains several sets of DNA. Triploid (3n), tetraploid (4n), pentaploid (5n), and other polyploids are examples.

Haploid Examples
i. Haploid Cells in Humans

Hemiploid cells include sex cells (gametes). The somatic cell in humans (as well as other higher forms of life) has two copies of genes. As a result, they are known as diploids. They generate haploid gametes by gametogenesis, which uses meiosis to split the chromosome set in half.

This is necessary to ensure that the resultant zygote is diploid following the fusion of gametes. This ensures that chromosomal number integrity is maintained throughout generations. Human sex cells (sperm or egg cells) contain 23 chromosomes in particular.

This indicates that the diploid number of sperm and egg cells is half that of a human somatic cell (which is 46). The two cells join during fertilisation, creating a zygote with two sets of chromosomes. The human zygote then develops through the process of mitosis. As a result, the archetypal human chromosomal number of 46 per somatic cell in the body is preserved.

ii. Plant Gametophyte

Plants have two generations in their life cycle: the gametophyte and the sporophyte. A gametophyte is a stage in the life cycle of a plant or the plant itself that carries gametes. As a result, a gametophyte, such as the embryophytes, is a haploid multicellular form of the plant.

Haploid Citations
  • Breeding Maize Maternal Haploid Inducers. Plants (Basel) . 2020 May 12;9(5):614.
  • Haploid Induction and Genome Instability. Trends Genet . 2019 Nov;35(11):791-803.
  • Haploid animal cells. Development . 2014 Apr;141(7):1423-6.
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