Haploids have one set of chromosomes (n=1), which is the same as a gamete (pollen or egg cell). Haploids can be distinguished from diploids (n=2) by using gene markers which are closely linked with the gene under study so they can be visually detected or by their physical characteristics. They are used in plant breeding to obtain pure lines that are homozygous by using colchicine to double the chromosome number, or by relying on spontaneous mutations.
A doubled haploid has two sets of chromosomes identical to the haploid and can form pollen and egg cells like a diploid plant, whereas, a haploid is rarely able to produce pollen for self fertilization .
Some examples of plants in which haploidy is used for breeding purposes are: