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Recombination The process by which progeny derive a combination of linked genes different from that of either parent. In higher organisms, this can occur by crossing over between their loci during meiosis. Recombination may come about through random orientation of non-homologous chromosome pairs on the meiotic spindles, from crossing-over between homologous chromosomes, from gene conversion, or by other means. See homologous recombination.
Related Terms:
Gene The term coined by Johannsen (1909) for the fundamental physical and functional unit of heredity. The word gene was derived from De Vries' term pangen, itself a derivative of the word pangenesis which Darwin (1868) had coined. A gene is an ordered sequence of nucleotides located in a particular position (locus) on a particular chromosome that encodes a specific functional product (the gene product, i.e. a protein or RNA molecule). It includes regions involved in regulation of expression and regions that code for a specific functional product. See gene expression, allele.
Crossing over The term coined by Morgan and Cattell (1912) for the occurrence of new combinations of linked characters. With the acceptance of the chromosome theory, the term is applied to the breaking during meiosis of one maternal and one paternal chromosome, the exchange of corresponding sections of DNA, and the rejoining of the chromosomes. This process can result in an exchange of alleles between chromosomes and gives rise to new character combinations. Compare recombination.
Locus The position of a gene on a chromosome or other chromosome markers; also, the DNA at that position. The use of the term locus is sometimes restricted to main regions of DNA that are expressed. Plural: loci. See gene expression.
Meiosis The term coined by Farmer and Moore (1905) for the process of two consecutive cell divisions in the diploid progenitors of sex cells. Meiosis results in four rather than two daughter cells (gametes), each with a haploid set of each chromosome pair. In meiosis I the prophase is more complex than that of mitosis. Five different stages can be differentiated: leptotene, zygotene, pachytene, diplotene and diakinesis. Prophase is followed by metaphase I, anaphase I, telophase I and interkinesis. Meiosis II could be described as a haploid mitosis resulting in four haploid gametes.
Meiosis I   

Leptotene of prophase I

Zygotene of prophase I

Pachytene of prophase I

Diplotene of prophase I

Diakinesis of prophase I

Metaphase I

Anaphase I

Telophase I

Interkinesis
   
Meiosis II   
Homologous chromosome A pair of chromosomes containing the same linear gene sequences, each derived from one parent. Humans normally have 22 pairs of homologous chromosomes and 2 X chromosomes (female) or 1 X and 1 Y chromosome (male). Compare sex chromosomes.
Conversion The term proposed by Winkler (1930) for a process of interaction between alleles at meiosis. The term was re-introduced by Lindegren (1953) to account for aberrant ratios in the products of meiosis, apparently arising from such interaction. Whitehouse and Hastings (1965) have suggested that if gene conversion is due to the correction of mispairing of bases in DNA, it may give rise to reciprocal as well ac nonreciprocal recombination.
Homologous recombination Substitution of a segment of DNA by another that is identical (homologous) or nearly so. Occurs naturally during meiotic recombination; also used in the laboratory for gene targeting to modify the sequence of a gene. See recombination.

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Database: Birgid Schlindwein. Please contact me if you encounter any mistakes or if you are missing anything
© Dr. Birgid B. Schlindwein
last update of the database 10/01/2006