#zygote

• From the egg / From the very beginning — A Latin phrase derived from Horace's writings, meaning literally 'from the egg'. In embryology and developmental toxicology, it refers to analyzing a biological process, cellular mechanism, or the action of a teratogenic agent (malformation-inducing toxin) traced right from the egg-cell (zygote) stage or from the moment of fertilization to fully map fetal development disruptions.
• 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.
• Amphicaryon — A hybrid, diploid cell nucleus, structurally formed following the process of amphimixis through the complete fusion of two pronuclei (male and female) during egg fertilization. This zygotic nucleus contains the full set of chromosomes inherited from both parents, ensuring the combination and transmission of hereditary genetic material to subsequent generations.
• Amphigenetic — Relating to amphigenesis or originating from it; characterized by biparental sexual reproduction involving the hybrid fusion of two gametes of different sexes (male and female). From a structural perspective, it describes the normal ontogenetic process through which the new organism inherits complementary sets of genetic material from both parents, ensuring genomic variability within the species.
• Amphigenesis — A biological process of generating or arising a new organism through true sexual reproduction, requiring the equal participation and structural fusion of male and female reproductive elements (gametes). This phenomenon represents the evolutionary foundation of most higher organisms, being the opposite of asexual reproduction or clonal parthenogenesis.
• Amphigony — A normal form of biparental sexual reproduction requiring the structural and functional fusion of two gametes of opposite sexes, male and female, leading to the formation of a diploid zygote. This fundamental biological process represents the evolutionary basis of genetic variability within higher organisms, being the opposite of parthenogenesis or clonal asexual reproduction.
• Amphimixis — A fundamental biological process of true sexual reproduction, consisting of the structural fusion of two gametes of opposite sexes (the male and female pronuclei), leading to the formation of a diploid zygote (fertilized egg). This mechanism forms the basis of Mendelian genetic recombination, ensuring the transmission of parental hereditary traits and genomic diversity within the species.
• Amphiplasm — A hybrid cytoplasmic formation or unified protoplasmic mass, structurally formed during the early stages of amphimixis through the complete merging of the cytoplasm of both gametes (male and female). This stage precedes the actual nuclear fusion (karyogamy) and ensures the rearrangement of cellular organelles inside the newly developing zygote.
• 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.
• Androgamy — A specialized type of reproduction or fertilization (found in rare cases in certain plants, insects, or genetically modified organisms) where the zygote nucleus develops exclusively from the genetic material provided by the male gamete, while the female genetic material is structurally eliminated or inactivated.
• Autozygote — A zygote or diploid organism possessing identical alleles at a specific genetic locus, genes that have been inherited directly from a common ancestor through inbreeding or self-fertilization; an individual homozygous by direct descent (identity by descent).
• 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.