A nucleus, cell (usually reproductive) or organism having a single set or copy of unpaired chromosomes. Gametes, formed as a result of meiosis, are haploid in that the number of chromosomes is halved randomly. Fusion of two reproductive cells during fertilization restores the normal diploid number of chromosomes (viz., 46) as shown in the figure below.
Sexual reproduction separates out chromosomes in new combinations. Humans have 23 chromosomes in each gamete (only one chromosome is portrayed to aid interpretation). In eukaryote animals, cells proliferate in the diploid phase to form a multicellular organism.
See Acrosome, Chromosome, Diploid, Eukaryote cell (or organism), Gametes, Genetic (or DNA) recombination, Fertilization (or syngamy), Haploinsufficiency, Meiosis (reduction division), Mitosis