Ploidy breeding

Ploidy breeding

    • Ploidy refers to the number of sets of chromosomes in a biological cell.
    • Plant germ cells (pollen and ovule) have one complete set of chromosomes from the male or female parent.
    • Germ cells, also called gametes, combine to produce somatic cells.
    • Somatic cells therefore have twice as many chromosomes as that of germ cells. The haploid number ( n) is the number of chromosomes in a gamete.
    • A somatic cell has twice that many chromosomes (2n).


    • Euploidy is the state of a cell or organism having an integral multiple of the monoploid number, possibly excluding the sex-determining chromosomes.


    • Aneuploidy is the state of not having euploidy. In humans, examples include having a single extra chromosome (such as Down syndrome), or missing a chromosome (such as Turner syndrome).
    • Aneuploid karyotypes are given names with the suffix -somy (rather than -ploidy, used for euploid karyotypes), such as trisomy and monosomy.

    Haploid and monoploid

    • As stated above, the haploid number ( n) is the number of chromosomes in a gamete of an individual, and this is distinct from the monoploid number (x) which is the number of unique chromosomes in a single complete set.
    • Gametes (sperm, and ovary) are haploid cells.
    • The haploid gametes produced by (most) diploid organisms are monoploid, and these can combine to form a diploid zygote.
    • For example, most animals are diploid and produce monoploid gametes.
    • During meiosis, germ cell precursors have their number of chromosomes halved by randomly "choosing" one homologue, resulting in haploid gametes.
    • Because homologous chromosomes usually differ genetically, gametes usually differ genetically from one another.
    • All plants including algae and even many fungi switch between a haploid and a diploid state (which may be polyploid), with one of the stages emphasized over the other.
    • This is called alternation of generations. Most fungi and algae are haploid during the principal stage of their life cycle.
    • Male bees, wasps, and ants are haploid organisms because of the way they develop from unfertilized, haploid egg cells

Last modified: Monday, 2 April 2012, 7:21 PM