Haploid

HAPLOID, diploid (from Greek haploos-simple and diploos-double), terms denoting the numerical relationships of chromosomes in the nucleus (introduced by Strassburger in 1907). In a haploid nucleus, there is one chromosome of each type, while in a diploid nucleus there is a pair. The haploid number of chromosomes is present in sex cells after reduction division (see)-in "mature" sex cells. Diploid nuclei result from fertilization, after the fusion of two haploid (male and female) nuclei, and are generally found in all somatic cells. In some cases, during parthenogenetic reproduction, we find the haploid number of chromosomes even in somatic cells (drone). The rule that the diploid number equals twice the haploid number is undoubtedly valid only in cases where both sexes have the same number and form of chromosomes. If there are sex chromosomes, this rule applies only to one sex (in most cases female), where in the haploid nucleus the sex chromosomes (X-chromosomes) are present in single number, and in the diploid-in double. In the other sex, all chromosomes except the sex chromosomes are represented in the haploid nucleus in single number, and in the diploid-in double. As for the sex chromosomes, in some cases there is one unpaired sex chromosome in diploid cells (X-chromosome); in other cases there are two unpaired sex chromosomes (X and Y). Haploid nuclei in such cases are of two types: in the first case-with an X-chromosome and without it, in the second-some nuclei with an X-chromosome, others-with a Y-chromosome. Thus, the number of chromosomes in a diploid nucleus for a sex with different haploid nuclei can be represented as follows: 2n+x+y (if y is present), where n is the number of autosomes; the haploid number in some cells is n+x, in others n+y. For the other sex, the diploid number is 2n+2x, the haploid number is n+x in all cells. When there are multiple X-chromosomes, the double relationship between the number of chromosomes in haploid and diploid nuclei is even more disrupted. Then this relationship can be represented as follows: for one sex with different haploid nuclei, the diploid number = 2n + ax + y (if y exists), where a is the number of X-chromosomes; haploid = n+ax and n+y. For the other sex, diploid = 2n + 2ax, haploid = n+ax. For example, in the bug Gelastocoris oculatus, the male haploid number is 16 = 15+2y and 19 = 15+4x, diploid is 35=30 +4x+y; in the female, haploid is 19=15+4x, diploid is 38=30+8x; in another bug Syromastes marginatus, which has no Y-chromosome, in males the haploid number is 10 and 12 = 10 +2x, diploid is 22 = 20+2x; in females the haploid number is 12 = 10 +2x, diploid is 24=20+4x. In women, the haploid number of chromosomes is 24=23 +x, while in men it is either also 24 = 23 +y or else 24=23 +x (according to other authors, 23, y is absent).

L. Kursanov. In animals, haploid nuclei are present only in sex cells, while the entire body is diploid. In plants, the relationships are more complex, as both haploid and diploid states can develop into independent individuals that alternate properly in the developmental cycle (alternation of generations). In particular, in seed plants, the diploid state predominates, while the haploid state is represented only by the pollen tube and embryo sac, consisting of a few cells and not having an independent existence. In ferns, both states exist independently, although here the haploid state (gametophyte) is inferior in size and complexity of organization to the diploid (the actual fern). In some marine brown and red algae, both states are developed equally and are often indistinguishable in appearance, but differ in that the haploid state develops sexual organs (sexual generation), while the diploid develops asexual reproduction organs (asexual generation). In green algae, as a rule, the entire body is haploid, and the diploid nucleus is contained only in the zygote. During its germination, reduction division occurs. Finally, in higher fungi (see Fungi), the diploid state alternating with the haploid contains haploid nuclei in its cells, but paired and dividing simultaneously. Each such pair of haploid nuclei corresponds to one diploid nucleus.