Biology

Sperm

are male gametes, reproductive cells that contain half a set of chromosomes that can be joined with a female gamete to form a zygote. If allowed to develop, the zygote will turn into an embryo and eventually will mature into a baby. Male gametes are found in semen, a fluid produced by men for the purpose of reproduction. The composition of semen varies, but sperm as a general rule make up only a very small percentage, usually less than five percent, of the volume.

Gametogenesis

is a biological process by which diploid or haploid precursor cells undergo cell division and differentiation to form mature haploid gametes. Depending on the biological life cycle of the organism, gametogenesis occurs by meiotic division of diploid gametocytes into various gametes, or by mitotic division of haploid gametogenous cells. For example, plants produce gametes through mitosis in gametophytes. The gametophytes grow from haploid spores after sporic meiosis. The existence of a multicellular, haploid phase in the life cycle between meiosis and gametogenesis is also referred to as alternation of generations.

Fertilization

the action or process of fertilizing an egg, female animal, or plant, involving the fusion of male and female gametes to form a zygote.

Homologous chromosomes

A couple of homologous chromosomes is a set of one maternal chromosome and one paternal chromosome that pair up with each other inside a cell during mitosis. These copies have the same genes in the same locations, or loci. These loci provide points along each chromosome which enable a pair of chromosomes to align correctly with each other before separating during mitosis.

Diploid

is a cell or organism that has paired chromosomes, one from each parent. In humans, cells other than human sex cells, are diploid and have 23 pairs of chromosomes. Human sex cells (egg and sperm cells) contain a single set of chromosomes and are known as haploid.

Autosome

is a chromosome that is not an allosome. Autosomes appear in pairs whose members have the same form but differ from other pairs in a diploid cell, whereas members of an allosome pair may differ from one another and thereby determine sex. The DNA in autosomes is collectively known as atDNA or auDNA. For example, humans have a diploid genome that usually contains 22 pairs of autosomes and one allosome pair (46 chromosomes total).

Sexual reproduction

is a process that creates a new organism by combining the genetic material of two organisms in a process that starts with meiosis, a specialized type of cell division. It occurs in eukaryotes.[1][2] Prokaryotes display processes similar to sex (mechanisms for lateral gene transfer such as bacterial conjugation, transformation and transduction), but they do not lead to reproduction. Prokaryotes reproduce through asexual reproduction. In multicellular eukaryote organisms, an individual is created anew; in prokaryotes, the initial cell has additional or transformed genetic material. In a process called genetic recombination, genetic material (DNA) originating from two different individuals join up so that homologous sequences are aligned with each other, and this is followed by exchange of genetic information. After the new recombinant chromosome is formed, it is passed on to progeny.

Meiosis

is a specialized type of cell division which reduces the chromosome number by half. This process occurs in all sexually reproducing eukaryotes (both single-celled and multicellular) including animals, plants, and fungi.

Somatic cell

is any biological cell forming the body of an organism; that is, in a multicellular organism, any cell other than a gamete, germ cell, gametocyte or undifferentiated stem cell. In contrast, gametes are cells that fuse during sexual reproduction, germ cells are cells that give rise to gametes, and stem cells are cells that can divide through mitosis and differentiate into diverse specialized cell types.

Egg

is the organic vessel containing the zygote in which an animal embryo develops until it can survive on its own, at which point the animal hatches. An egg results from fertilization of an ovum. Most arthropods, vertebrates, and mollusks lay eggs, although some do not, such as scorpions and most mammals.

Gamete

A gamete (from Ancient Greek γαμετή gamete "wife"[1]) is a cell that fuses with another cell during fertilization (conception) in organisms that sexually reproduce. In species that produce two morphologically distinct types of gametes, and in which each individual produces only one type, a female is any individual that produces the larger type of gamete—called an ovum (or egg)—and a male produces the smaller tadpole-like type—called a sperm. This is an example of anisogamy or heterogamy, the condition in which females and males produce gametes of different sizes (this is the case in humans; the human ovum has approximately 100,000 times the volume of a single human sperm cell[2][3]). In contrast, isogamy is the state of gametes from both sexes being the same size and shape, and given arbitrary designators for mating type. The name gamete was introduced by the Austrian biologist Gregor Mendel. Gametes carry half the genetic information of an individual, one ploidy of each type, and are created through meiosis.

Sex chromosomes

A type of chromosome in the genome that is involved in the determination of the sex as well as the development of sexual characteristics in an organism. It occurs in pairs in somatic cells while singly in sex cells (gametes).

Polar body

When certain diploid cells in animals undergo cytokinesis after meiosis to produce egg cells, they sometimes divide unevenly. Most of the cytoplasm is segregated into one daughter cell, which becomes the egg or ovum. The other, smaller cells are called polar body.