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25 November, 04:30

In Drosophila, singed bristles [sn] and cut wings [ct] are both caused by recessive X-linked alleles. The wild type alleles [sn + and ct+] are responsible fro straight bristles and intact wings, respectively. A female homozygous for sn and ct + is crossed to a sn + ct male. The F1 flies are interbred. The F2 males are distributed as follows:

sn ct 13

sn ct + 36

sn + ct 39

sn + ct + 12

What is the map distance bwteen sn and ct?

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  1. 25 November, 04:54
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    The map distance between sn and ct is = 25 m. u or map unit.

    Explanation:

    Given, sn ct + * sn + ct

    In F1 generation the progenies were interbred.

    In F2 generation,

    sn ct = 13 (recombinant)

    sn ct + = 36 (parental)

    sn + ct = 39 (parental)

    sn + ct + = 12 (recombinant)

    Linkage Map distance = (no. of Recombinant progeny/total progeny)

    * 100

    Recombination frequency = (no. of Recombinant progeny/total progeny)

    * 100

    = (13 + 12) / 100 * 100 m. u

    = 25/100 * 100

    = 25 %

    ∴ The distance between sn and ct = 25 m. u or map unit

    ∴ Linkage happened between sn and ct as the map distance is much less than 50
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