biology 03

Sexual reproduction

the production of offspring through the union of male and female gametes (e.g., eggs and sperm)

Meiosis

specialized process of cell division that, in animals, produces gametes

Gametes

have half the number of chromosomes present in the somatic cells (body cells) of a species

Zygote

formed when the nuclei of an egg and a sperm cell fuse at fertilization; the chromosome number is restored

Fertilization

the nuclei of an egg and a sperm cell fuse, producing a zygote

Gonads

primary reproductive organs where meiosis takes place

Spermatozoa

gametes of the male produced in testes

Ova

gametes of the female produced in ovaries

Gametogenesis

the cellular mechanism of gamete formation

Alleles

versions of each gene present in the members of a homologous pair; may be the same or different

Crossing over

the physical exchange of chromosome segments between nonsister chromatids of homologous chromosomes during meiosis I.

Chiasmata

thickened spots marking sites where crossing-over occurred

Synapsis

the pairing of homologous chromosomes during prophase I to form tetrads

Independent assortment

random segregation of homologous chromosomes to the poles during anaphase I

Genetic recombination

the exchange of DNA between homologous chromosomes (via crossing-over), producing genetic variability