Hypermedia Glossary Of Genetic Terms
|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.|
|Allele||The term coined by Bateson and Saunders (1902) for characters which are alternative to one another in Mendelian inheritance (Gk. Allelon, one another; morphe, form).
Now the term allele is used for two or more alternative forms of a gene resulting in different gene products and thus different phenotypes. In a haploid set of chromosomes there is only one allele at its specific locus. Diploid organisms have 2 alleles at a given locus, i.e. a normal and a mutant allele. A single allele for each gene locus is inherited separately from each parent (e.g., at a locus for eye colour the allele might result in blue or brown eyes). An organism is homozygous for a gene if the alleles are identical, and heterozygous if they are different.
|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.
|Mispairing||The presence of a nucleotide in one nucleotide chain of a DNA molecule, which is not the complement of that at the corresponding position in the other chain.|
|Deoxyribonucleic acid (DNA)||The molecule that encodes genetic information. DNA is a double-stranded molecule held together by weak bonds between base pairs of nucleotides. The four nucleotides in DNA contain the bases: adenine (A), guanine (G), cytosine (C), and thymine (T). In nature, base pairs form only between A and T and between G and C; thus the base sequence of each single strand can be deduced from that of its partner.|
|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.|
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