Middle School Life Science: Cell Division, Reproduction, and Protein Synthesis - Reproduction — Flashcards

Reproduction is how organisms produce offspring. The ability to reproduce is a characteristic of all living things. In some species, all the offspring are genetically identical to the parent. In other species, each offspring is genetically unique. Why does this happen in some species but not others? It's because there are two types of reproduction.    
Reproduction can be sexual or asexual.    
Asexual reproduction is simpler than sexual reproduction. It involves just one parent. The offspring are genetically identical to each other and to the parent. All prokaryotes and some eukaryotes reproduce this way. There are several different methods of asexual reproduction, including binary fission, fragmentation, and budding.    
Sexual reproduction is more complicated. It involves two parents. Special cells called gametes are produced by the parents. A female parent produces gametes called eggs, and a male parent produces gametes called sperm. An offspring forms when an egg and a sperm unite, a process that is called fertilization. The initial cell that forms when the egg and sperm unite is called a zygote.    
Unlike other body cells, gametes are haploid cells. They have only one copy of each type of chromosome. Gametes are produced in a special type of cell division called meiosis.

Meiosis is basically mitosis times two. During meiosis, an original diploid cell divides twice (meiosis I and meiosis II). However, the DNA in the cell replicates just once (only before meiosis I). The result is four genetically different daughter cells, each with the haploid number of chromosomes.