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Unformatted text preview: break and may be reattached to a different homologous chromosome. The alleles on this tetrad: A B C D E F G A B C D E F G a b c d e f g a b c d e f g will produce the following chromosomes if there is a crossing-over event between the 2nd and 3rd chromosomes from the top: A B C D E F G A B c d e f g a b C D E F G a b c d e f g Thus, instead of producing only two types of chromosome (all capital or all lower case), four different chromosomes are produced. This doubles the variability of gamete genotypes. The occurrence of a crossing-over is indicated by a special structure, a chiasma (plural chiasmata) since the recombined inner alleles will align more with others of the same type (e.g. a with a, B with B). Near the end of Prophase I, the homologous chromosomes begin to separate slightly, although they remain attached at chiasmata....
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