Gametogenesis: The process of germ cell development from the primordial GERM CELLS to the mature haploid GAMETES: ova in the female (OOGENESIS) or sperm in the male (SPERMATOGENESIS).Gametogenesis, Plant: The process of germ cell development in plants, from the primordial PLANT GERM CELLS to the mature haploid PLANT GAMETES.Spermatogenesis: The process of germ cell development in the male from the primordial germ cells, through SPERMATOGONIA; SPERMATOCYTES; SPERMATIDS; to the mature haploid SPERMATOZOA.Germ Cells: The reproductive cells in multicellular organisms at various stages during GAMETOGENESIS.Oogenesis: The process of germ cell development in the female from the primordial germ cells through OOGONIA to the mature haploid ova (OVUM).Meiosis: A type of CELL NUCLEUS division, occurring during maturation of the GERM CELLS. Two successive cell nucleus divisions following a single chromosome duplication (S PHASE) result in daughter cells with half the number of CHROMOSOMES as the parent cells.Testis: The male gonad containing two functional parts: the SEMINIFEROUS TUBULES for the production and transport of male germ cells (SPERMATOGENESIS) and the interstitial compartment containing LEYDIG CELLS that produce ANDROGENS.Genomic Imprinting: The variable phenotypic expression of a GENE depending on whether it is of paternal or maternal origin, which is a function of the DNA METHYLATION pattern. Imprinted regions are observed to be more methylated and less transcriptionally active. (Segen, Dictionary of Modern Medicine, 1992)Pollen: The fertilizing element of plants that contains the male GAMETOPHYTES.Spermatocytes: Male germ cells derived from SPERMATOGONIA. The euploid primary spermatocytes undergo MEIOSIS and give rise to the haploid secondary spermatocytes which in turn give rise to SPERMATIDS.Reproduction: The total process by which organisms produce offspring. (Stedman, 25th ed)Ovary: The reproductive organ (GONADS) in female animals. In vertebrates, the ovary contains two functional parts: the OVARIAN FOLLICLE for the production of female germ cells (OOGENESIS); and the endocrine cells (GRANULOSA CELLS; THECA CELLS; and LUTEAL CELLS) for the production of ESTROGENS and PROGESTERONE.XanthurenatesGonads: The gamete-producing glands, OVARY or TESTIS.Ovule: The element in plants that contains the female GAMETOPHYTES.Vitellogenesis: The active production and accumulation of VITELLINS (egg yolk proteins) in the non-mammalian OOCYTES from circulating precursors, VITELLOGENINS. Vitellogenesis usually begins after the first MEIOSIS and is regulated by estrogenic hormones.Helleborus: A plant genus of the family RANUNCULACEAE. Members contain hellebrin (BUFANOLIDES). The extract is the basis of Boicil preparation used to treat rheumatism.Spermatozoa: Mature male germ cells derived from SPERMATIDS. As spermatids move toward the lumen of the SEMINIFEROUS TUBULES, they undergo extensive structural changes including the loss of cytoplasm, condensation of CHROMATIN into the SPERM HEAD, formation of the ACROSOME cap, the SPERM MIDPIECE and the SPERM TAIL that provides motility.Meiotic Prophase I: The prophase of the first division of MEIOSIS (in which homologous CHROMOSOME SEGREGATION occurs). It is divided into five stages: leptonema, zygonema, PACHYNEMA, diplonema, and diakinesis.Spores, Fungal: Reproductive bodies produced by fungi.Oocytes: Female germ cells derived from OOGONIA and termed OOCYTES when they enter MEIOSIS. The primary oocytes begin meiosis but are arrested at the diplotene state until OVULATION at PUBERTY to give rise to haploid secondary oocytes or ova (OVUM).Gene Expression Regulation, Developmental: Any of the processes by which nuclear, cytoplasmic, or intercellular factors influence the differential control of gene action during the developmental stages of an organism.Molecular Sequence Data: Descriptions of specific amino acid, carbohydrate, or nucleotide sequences which have appeared in the published literature and/or are deposited in and maintained by databanks such as GENBANK, European Molecular Biology Laboratory (EMBL), National Biomedical Research Foundation (NBRF), or other sequence repositories.Arabidopsis: A plant genus of the family BRASSICACEAE that contains ARABIDOPSIS PROTEINS and MADS DOMAIN PROTEINS. The species A. thaliana is used for experiments in classical plant genetics as well as molecular genetic studies in plant physiology, biochemistry, and development.Fertility: The capacity to conceive or to induce conception. It may refer to either the male or female.Hermaphroditic Organisms: Animals and plants which have, as their normal mode of reproduction, both male and female sex organs in the same individual.Embryonic Development: Morphological and physiological development of EMBRYOS.snRNP Core Proteins: The protein components that constitute the common core of small nuclear ribonucleoprotein particles. These proteins are commonly referred as Sm nuclear antigens due to their antigenic nature.Arabidopsis Proteins: Proteins that originate from plants species belonging to the genus ARABIDOPSIS. The most intensely studied species of Arabidopsis, Arabidopsis thaliana, is commonly used in laboratory experiments.Spermatogonia: Euploid male germ cells of an early stage of SPERMATOGENESIS, derived from prespermatogonia. With the onset of puberty, spermatogonia at the basement membrane of the seminiferous tubule proliferate by mitotic then meiotic divisions and give rise to the haploid SPERMATOCYTES.DNA Methylation: Addition of methyl groups to DNA. DNA methyltransferases (DNA methylases) perform this reaction using S-ADENOSYLMETHIONINE as the methyl group donor.Disorders of Sex Development: In gonochoristic organisms, congenital conditions in which development of chromosomal, gonadal, or anatomical sex is atypical. Effects from exposure to abnormal levels of GONADAL HORMONES in the maternal environment, or disruption of the function of those hormones by ENDOCRINE DISRUPTORS are included.Cyclin A1: A cyclin A subtype primarily found in male GERM CELLS. It may play a role in the passage of SPERMATOCYTES into meiosis I.Mutation: Any detectable and heritable change in the genetic material that causes a change in the GENOTYPE and which is transmitted to daughter cells and to succeeding generations.Proto-Oncogene Proteins c-kit: A protein-tyrosine kinase receptor that is specific for STEM CELL FACTOR. This interaction is crucial for the development of hematopoietic, gonadal, and pigment stem cells. Genetic mutations that disrupt the expression of PROTO-ONCOGENE PROTEINS C-KIT are associated with PIEBALDISM, while overexpression or constitutive activation of the c-kit protein-tyrosine kinase is associated with tumorigenesis.Infertility, Male: The inability of the male to effect FERTILIZATION of an OVUM after a specified period of unprotected intercourse. Male sterility is permanent infertility.DNA (Cytosine-5-)-Methyltransferase: An enzyme that catalyzes the transfer of a methyl group from S-ADENOSYLMETHIONINE to the 5-position of CYTOSINE residues in DNA.Haploidy: The chromosomal constitution of cells, in which each type of CHROMOSOME is represented once. Symbol: N.Base Sequence: The sequence of PURINES and PYRIMIDINES in nucleic acids and polynucleotides. It is also called nucleotide sequence.Infertility: Inability to reproduce after a specified period of unprotected intercourse. Reproductive sterility is permanent infertility.Amino Acid Sequence: The order of amino acids as they occur in a polypeptide chain. This is referred to as the primary structure of proteins. It is of fundamental importance in determining PROTEIN CONFORMATION.Life Cycle Stages: The continuous sequence of changes undergone by living organisms during the post-embryonic developmental process, such as metamorphosis in insects and amphibians. This includes the developmental stages of apicomplexans such as the malarial parasite, PLASMODIUM FALCIPARUM.Sex Differentiation: The process in developing sex- or gender-specific tissue, organ, or function after SEX DETERMINATION PROCESSES have set the sex of the GONADS. Major areas of sex differentiation occur in the reproductive tract (GENITALIA) and the brain.Zygote: The fertilized OVUM resulting from the fusion of a male and a female gamete.Chlamydomonas: A genus GREEN ALGAE in the order VOLVOCIDA. It consists of solitary biflagellated organisms common in fresh water and damp soil.