Linkage and Crossing Over

Also called

linkage · crossing over · recombination · Morgan · Drosophila · fruit fly · chiasma · chiasmata · linked genes · recombinant · parental type · genetic map · linkage map · map distance · centimorgan · Sturtevant · सहलग्नता · जीन विनिमय · पुनर्संयोजन

Topics

• Morgan crossed fruit flies (Drosophila) and found that some pairs of genes did not assort independently.
• Genes close together on one chromosome are linked: they are passed on together, as one block.
• Yellow body and white eye lie close together on the X chromosome: only 1.3 % of offspring were recombinant.
• White eye and miniature wing lie far apart on it: 37.2 % of the offspring had new combinations.
• In prophase I of meiosis homologous chromosomes pair; two non-sister chromatids touch at a chiasma.
• At the chiasma the chromatids break and rejoin, swapping segments: this is crossing over.
• One crossover gives two parental and two recombinant chromatids, so two kinds of new gametes.
• The farther apart two genes are, the more often a crossover falls between them.
• Sturtevant used recombination frequency as map distance: 1 % recombination is 1 map unit (centimorgan).

About this model

A GLB file of about 403 KB, shown in Lably's 3D viewer and, on a phone, placed in your room with AR. Credit: Model, science and animation: Lably (built procedurally with three.js; no downloaded meshes). | CC BY 4.0. Original geometry and animation made for Lably.

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