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Thomas Hunt Morgan's illustration of crossing over (1916) In eukaryotes, recombination during meiosis is facilitated by chromosomal crossover. The crossover process leads to offspring having different combinations of genes from those of their parents, and can occasionally produce new chimeric alleles. The shuffling of genes brought about by genetic recombination produces increased genetic variation. It also allows sexually reproducing organisms to avoid Muller's ratchet, in which the genomes of an asexual population accumulate deleterious mutations in an irreversible manner. Chromosomal crossover involves recombination between the paired chromosomes inherited from each of one's parents, generally occurring during meiosis. During prophase I (pachytene stage) the four available chromatids are in tight formation with one another. While in this formation, homologous sites on two chromatids can closely pair with one another, and may exchange genetic information. Because recombination can occur with small probability at any location along chromosome, the frequency of recombination between two locations depends on the distance separating them. Therefore, for genes sufficiently distant on the same chromosome the amount of crossover is high enough to destroy the correlation between alleles. Tracking the movement of genes resulting from crossovers has proven quite useful to geneticists. Because two genes that are close together are less likely to become separated than genes that are farther apart, geneticists can deduce roughly how far apart two genes are on a chromosome if they know the frequency of the crossovers. Geneticists can also use this method to infer the presence of certain genes. Genes that typically stay together during recombination are said to be linked. One gene in a linked pair can sometimes be used as a marker to deduce the presence of another gene. This is typically used in order to detect the presence of a disease-causing gene. #recessive #nucleicAcid #GeneticTesting #Allele #enzyme #inheritance #aminoAcid #genetic #genes #Eukaryotic #MolecularBiology #breedingExperiment #genotypes #genomics #metaphase #RnaSplicing #PaternityTest #Primers #gene #GeneticsExamQuestionsSolutions #transcription #codons #Haploid #nucleicAcids #GeneticsLecture #Prokaryotes #Chromosomes #locus #DNA #phenotype #GeneticsFieldOfStudy #RecombinantDNAInvention
