#cytogenetics

• 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.
• Amphidiploidy — A genetic state or a particular type of polyploidy (allopolyploidy) characterized by the presence of a complete diploid set of chromosomes derived from two different parental species following hybridization and subsequent chromosome doubling. This structural phenomenon guarantees the fertility of the hybrid, allowing normal pairing of homologous chromosomes during meiosis, and is widely used in plant genetic engineering to create new plant varieties.
• Amphiplasty — A cytogenetic phenomenon or structural chromosomal anomaly arising following interspecific hybridization, characterized by the constant morphological modification (alteration of shape, secondary constrictions, or nucleolar organizers) of one set of chromosomes derived from one parental species under the influence of the cytoplasm or genome of the partner species.
• 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.
• Aneuploidy — A numerical genetic anomaly consisting of a change in the normal number of chromosomes within a cell or organism, through the loss or gain of one or more chromosomes from the basic diploid set. This structural phenomenon usually occurs as a result of chromosome nondisjunction during meiosis or mitosis and represents a major cause of severe phenotypic developmental disorders and spontaneous abortions.
• 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.
• Autopolyploidy — A structural genomic state or mutation characterized by the presence of more than two complete sets of homologous chromosomes within the cell nucleus, derived entirely from the same species due to endogenous duplication of genetic material without interspecific hybridization. This phenomenon occurs through the disruption of cell division (mitotic or meiotic non-disjunction) and plays a major role in the evolution and diversification of the plant kingdom, frequently causing morphological changes such as increased cell and organ size, as well as enhanced plant resilience.
• Azygote — A haploid organism or cell resulting from a parthenogenetic developmental process, without prior fertilization of gametes; an individual that develops directly from an unfertilized egg, possessing a single set of chromosomes and lacking paired genes.