#chromosome

• Aberrant / Anomalous — Deviating evidently from the normal type, standard anatomical structure, or natural physiological course. In genetics and oncology, it qualifies atypically developed cells, chromosomes, or blood vessels; in psychiatry, it describes a profoundly distorted behavior, reasoning, or emotional response incompatible with medical logic or objective reality.
• Chromocenter — A microscopic nuclear structure formed by the fusion or aggregation of the pericentromeric heterochromatic regions (centromeres) of multiple chromosomes during cellular interphase. This dense structural formation, frequently observed within the salivary glands of certain insects (such as the polytene chromosomes of Drosophila), appears under the microscope as an intensely stainable central mass from which the euchromatic chromosomal arms radiate, lacking direct transcriptional activity in that zone.
• 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.
• DNA — Deoxyribonucleic acid; a complex macromolecule formed by a double helical strand of nucleotides, which constitutes the material basis of genetic information in all living organisms and most viruses. Structurally, it contains the genes responsible for heredity, development, and biological functioning, primarily located within the cell nucleus.
• Allele — One of the alternative forms or molecular variants of the same gene, structurally located at the same locus on a homologous chromosome. Alleles determine different variations of the same phenotypic trait (such as eye color or blood type), interacting with each other through relations of dominance, recessiveness, codominance, or incomplete dominance within diploid organisms.
• The alleles — The definite articulate plural form of the feminine noun alelă; it specifically and directly defines the alternative variants of the same gene occupying a homologous chromosomal locus, viewed as clearly defined objects of study within a diploid organism or a biological population.
• Allelism — The state, property, or biological phenomenon whereby a gene possesses multiple alternative forms or mutant variants (alleles) occupying the same locus on homologous chromosomes. Structurally, this concept underscores genetic diversity within a population, analyzed in Mendelian inheritance studies to explain the functional interactions between phenotypic traits transmitted to offspring.
• Allelomorph — 1. One of the alternative forms or molecular variants of the same gene, occupying the same locus on a homologous chromosome and controlling different variations of the same phenotypic trait; an allele. 2. Presenting allelomorphic characteristics, structures, or properties, belonging to a pair of alternative genes that interact through relations of dominance or recessiveness.
• Allelomorphism — The state, quality, or biological phenomenon whereby a gene presents itself in the form of multiple alternative variants (allelomorphs or alleles) capable of occupying the same chromosomal locus. This structural concept underscores genetic variability within populations, explaining how paired genes interact to produce phenotypic diversity.
• Allelomorphism — The state, property, or biological phenomenon whereby a single gene possesses multiple alternative forms or molecular variants (alleles) capable of occupying the same chromosomal locus. In population genetics, this structural mechanism represents the central pillar of gene polymorphism, determining the complex ways in which paired genes interact through dominance, recessiveness, or codominance to generate the diversity of hereditary traits.
• 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).
• Allopolyploid — An organism, cell, or individual possessing more than two complete sets of chromosomes (being polyploid), resulting from the hybridization between two or more distinct species, followed by chromosome doubling. This hybrid structural phenomenon combines non-homologous genomes, being extremely widespread in the plant kingdom (for instance, in wheat or cotton), where it ensures enhanced vigor and restored fertility.
• Allopolyploidy — The state, property, or structural phenomenon consisting of the presence of more than two chromosome sets originating from distinct species following interspecific hybridization. Allopolyploidy represents a major evolutionary engine in the plant kingdom, allowing the instantaneous emergence of new, fertile species reproductively isolated from their parents, combining the genetic advantages of both ancestral lines.
• 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.
• Allosome — A sex chromosome or heterochromosome that differs structurally in size, shape, and genetic behavior from regular somatic chromosomes (autosomes). This type of chromosomal element (such as the X and Y chromosomes in mammals) plays the pivotal role in the genetic determination of an individual's sex and in the transmission of sex-linked hereditary traits.
• Allozygote — A diploid organism or cell (zygote) in which the two alleles at a specific gene locus originate from completely independent and distinct ancestors, lacking a recent common origin (identical by state, but not by descent). This structural mechanism opposes the concept of an homozygote by descent (autozygote), serving as a baseline indicator of genetic variability and the absence of inbreeding within a population.
• Allosome — A sex chromosome or heterochromosome that differs structurally in size, shape, and genetic behavior from regular somatic chromosomes (autosomes). This type of chromosomal element (such as the X and Y chromosomes in mammals) plays the pivotal role in the genetic determination of an individual's sex and in the transmission of sex-linked hereditary traits.
• Amphidiploid — A polyploid organism or cell formed through the hybridization of two different species, followed by the doubling of the chromosome set, thus containing the complete diploid sets of both parental species. As an adjective, it describes a genetically stabilized genome, plant, or agricultural crop (such as triticale) capable of normal fertile reproduction because each chromosome finds its homologue during meiosis.
• 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.