#meiosis

• Acrosyndesis — A cytogenetic phenomenon or particular type of meiotic synapsis characterized by the pairing, association, or partial fusion of homologous chromosomes exclusively at their distal extremities (telomeres or terminal regions), while the intercalary and centromeric segments remain free and unaligned. This restrictive chromosomal structure directly influences the crossing-over process and the genetic recombination rate within those specific zones.
• Allocyclies — An atypical mitotic or meiotic behavior of certain chromosomes or chromosomal segments (especially heterochromatin), structurally characterized by a desynchronized rhythm of condensation and replication compared to the rest of the chromosomal complement in the nucleus; it can be positive (precocious condensation) or negative (delayed condensation).
• Allosyndesis — A cytogenetic phenomenon or structural process consisting of the pairing (synapsis) during meiosis of non-homologous chromosomes originating from different parents or distinct species within a hybrid or allopolyploid organism. This type of atypical chromosomal association differs structurally from autosynapsis and plays an essential role in analyzing genomic reconfiguration and the degree of phylogenetic relationship between taxa.
• Ameiosis — A special type of aberrant or modified cell division in which classic meiosis is not completed or is entirely replaced, resulting in reproductive cells (gametophytes or spores) that retain the unchanged diploid chromosome number of the parent cell (without chromatic reduction). This structural phenomenon is closely linked to the process of apomixis in certain plant species, allowing asexual reproduction through genetically viable seeds.
• Amphitene — A transient stage in the prophase of the first meiotic division, occurring between leptotene and pachytene, synonymous with zygotene, during which homologous chromosomes begin to align and pair up through synapsis. In this structural phase, the chromatid threads often present a characteristic bouquet arrangement, with one end thickened and the other thin during the pairing process.
• Anaphase — The third consecutive stage of the cell division process (mitosis or meiosis), structurally characterized by the abrupt separation and simultaneous migration of sister chromatids or homologous chromosomes toward the opposite poles of the cell. This mechanical and biological phenomenon, coordinated by the contraction of the mitotic spindle fibers, guarantees the perfectly equal and exact distribution of the duplicated genetic material to the two future daughter cells.
• Apomeiosis — A modified type of cell division where the normal process of meiosis is partially or completely suppressed or fails, resulting in the formation of a gametophyte or embryo sac with an unchanged (diploid) chromosome number; the cytological pillar of apomixis. This phenomenon ensures clonal seed production in plants, eliminating standard genetic segregation and meiotic recombination.
• Artioploid — An organism or polyploid cell that possesses an even number of complete chromosome sets (for example, tetraploid, hexaploid, octaploid); relating to this numerical condition of the genome. In plant and evolutionary genetics, this structure ensures higher meiotic stability compared to perissoploid (odd) forms, allowing normal fertility and regular genetic segregation.
• Ascospore — A microscopic spore with a sexual reproductive function, formed inside a special sac-like cell called an ascus, characteristic of fungi in the Ascomycota phylum. This structural element results from a sequential process of cell division (meiosis followed by mitosis), being released into the environment at maturity to germinate and form a new mycelium.
• Asynapsis — A structural biological phenomenon consisting of the absence or failure of alignment and pairing of homologous chromosomes during the prophase of the first meiotic division. This cellular structural anomaly prevents the formation of bivalents and the unfolding of the crossing-over process, frequently leading to aberrant chromosomal segregation, the formation of non-viable gametes, or the sterility of the affected organism.
• Autosyndesis — A genetic mechanism during meiosis in polyploid, particularly allopolyploid, organisms, characterized by the pairing (synapsis) and conjugation of homologous chromosomes derived from the same parental set or from the same ancestral species. This structural phenomenon differs from allosyndesis and plays a crucial role in maintaining genomic stability and determining inheritance patterns in complex plant hybrids.
• Auxocyte — An animal or plant germ cell during its stage of intense growth and development prior to entering the meiotic division process; a general term that encompasses primary spermatocytes and oocytes during their meiotic growth phase.