Chromosomal crossover

Chromosomal crossover is the process by which two chromosomes, paired up during Prophase I of meiosis, exchange some distal portion of their DNA. Crossover occurs when two chromosomes, normally two homologous instances of the same chromosome, break and then reconnect but to the different end piece. If they break at the same place or locus in the sequence of base pairs, the result is an exchange of genes. This outcome is the normal way for crossover to occur. If they break at slightly different loci, the result can be a duplication of genes on one chromosome and a deletion of these on the other. This is known as an unequal crossover. If chromosomes break and rejoin on opposite sides of the centromere, the result can be one chromosome being lost during cell division.

Related Topics:
Chromosomes - Meiosis - DNA - Chromosome - Homologous - Locus - Gene - Centromere - Cell division

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Any pair of homologous chromosomes may be expected to cross over three or four times during meiosis.

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This reduces the genetic linkage between genes on the same chromosome. The genetic variation of a population is thereby increased through chromosomal crossover. Independent assortment is a somewhat related process operating on the complete set of chromosomes.

Related Topics:
Genetic linkage - Independent assortment

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The physical basis of crossing over was first demonstrated by Harriet Creighton and Barbara McClintock in 1931.

Related Topics:
Harriet Creighton - Barbara McClintock - 1931

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