![]() ![]() During this period before cell divisions, genetic information is exchanged between homologous chromosomes in a process known as genetic recombination. After the DNA is replicated in meiosis, the homologous chromosomes pair up so that their DNA sequences are aligned with each other. ![]() This is followed by two cell divisions to generate haploid gametes. In meiosis, DNA is replicated to produce a total of four copies of each chromosome. ![]() In the production of gametes in eukaryotes, diploid precursor cells divide to produce haploid cells in a process called meiosis. Some proteins and other features that are key for sexual reproduction may have arisen in bacteria, but sexual reproduction is believed to have developed in an ancient eukaryotic ancestor. However, some process in bacteria may be considered analogous to sexual reproduction in that they incorporate new genetic information, including bacterial conjugation, transformation and transduction. Sexual reproduction does not occur in prokaryotes, unicellular organisms without cell nuclei, such bacteria and archaea. Sexual reproduction also occurs in some unicellular eukaryotes. Sexual reproduction is the most common life cycle in multicellular eukaryotes, such as animals, fungi and plants. This is typical in animals, though the number of chromosome sets and how that number changes in sexual reproduction varies, especially among plants, fungi, and other eukaryotes. ![]() Sexual reproduction is a type of reproduction that involves a complex life cycle in which a gamete ( haploid reproductive cells, such as a sperm or egg cell) with a single set of chromosomes combines with another gamete to produce a zygote that develops into an organism composed of cells with two sets of chromosomes ( diploid). During " fertilisation", haploid gametes come together to form a diploid zygote, and the original number of chromosomes is restored. In the first stage of sexual reproduction, " meiosis", the number of chromosomes is reduced from a diploid number (2n) to a haploid number (n). ![]()
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