Breeding of Vegetable, Spice and Tuber Crops

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

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

Aneuploidy

• 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