Definition of haploid

The term "haploid" in biology refers to a cell or organism that has only one set of chromosomes, whereas diploid cells and organisms possess two sets. The word "haploid" comes from the Greek word "haploos" meaning "single" or "onefold." The concept of haploidy was first introduced by the German biologist Richard Hertwig in 1906, during his studies of the marine polyp Corallium. He observed that the fertilized egg of Corallium developed directly into a multicellular organism without undergoing cell division, and this led him to propose the idea that the gametes of this species were haploid. Later, in the 1920s, Thomas Hunt Morgan Further solidified the term haploid in biology, after his observation that fruit flies with only one X chromosome (XO) were viable, and the presence of another X chromosome (XX) led to disease in females. These findings shed light on the fact that the presence of two X chromosomes in women is necessary for the normal development of ovaries, while in men, only one X chromosome is required. Nowadays, haploidy is no longer limited to gametes or certain organisms but also extends to certain life cycles of some plants and animals. For instance, in the reproduction of some flowers like lilies or orchids, after pollination, the resulting zygote is haploid instead of diploid. These plants possess specialized cells that double in number to produce diploid embryos, leading to diploid offspring. In summary, the term "haploid" is essential in genetics as it helps us understand the different stages in the reproductive life cycle of living organisms, from gametes to embryos, and eventually, the adults that result from the union of gametes.