One of two or more molecular forms of a gene at a given locus; alleles arise by mutation and encode slightly different versions of the same trait.
Any reproductive mode by which offspring arise from one parent and inherit that parent�s genes only; e.g., prokaryotic fission, transverse fission, budding, vegetative propagation.
Of a eukaryotic chromosome, a constricted region having binding sites (kinetochores) for spindle microtubules.
The sum of all of the chromosomes in cells of a given type.
A genetically identical copy of DNA, a cell, or a multicelled organism.
At prophase I of meiosis, reciprocal exchange of segments between two nonsister chromatids of a pair of homologous chromosomes. Puts novel combinations of alleles in gametes.
Of many sexually reproducing species, having two chromosomes of each type, or pairs of homologues, in somatic cells.
Mature female gamete, or ovum.
Fusion of a sperm nucleus and an egg nucleus, the result being a single-celled zygote.
Haploid cell formed by meiotic cell division of a reproductive cell; required for sexual reproduction.
[Gk. phyton, plant] A haploid multicelled body in which haploid gametes form during the life cycle of plants and some algae.
Unit of heritable information in DNA, transmissable from parents to offspring.
Outcome of any process that puts new genetic information in a DNA molecule; e.g., by crossing over.
Animal cell set aside for sexual reproduction; gives rise to gametes.
The sum of all chromosomes in cells with one of each type of chromosome characteristic of the species; e.g., in a gamete.
[Gk. homologia, correspondence] One of a pair of chromosomes in body cells of diploid organisms; except for a pairing of nonidentical sex chromosomes, a pair has the same size, shape, and gene sequence.
[Gk. meioun, to diminish] A nuclear division process that halves the parental chromosome number, to a haploid (n) number. Prerequisite to the formation of gametes and sexual spores.
A type of immature egg.
Mature secondary oocyte.
One of four cells that form by meiotic cell division of an oocyte but that does not become the ovum.
Production of genetically variable offspring by meiosis, gamete formation, and fertilization.
One of the two attached members of a duplicated eukaryotic chromosome.
Mature male gamete.
A structure of one or a few cells, often walled or coated, that protects and/or disperses a new sexual or asexual generation. Many bacteria as well as apicomplexans, fungi, and plants form spores.
[Gk. phyton, plant] A sporeproducing vegetative body of a plant or multicelled alga that grows by mitotic cell divisions from a zygote.