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Unformatted text preview: 10/21/09 1 What is the map distance between sn and ct ? A. 15 m.u. B. 18 m.u. C. 33 m.u. D. 49 m.u. E. 67 m.u. In Drosophila , singed bristles ( sn ) & cut wings ( ct ) are both caused by recessive, X‐linked alleles. The wild‐type alleles ( sn + and ct + ) are responsible for straight bristles and intact wings, respecPvely. A female homozygous for sn and ct + is crossed to a sn + ct male. The F 1 ﬂies are interbred. The F 2 males are distributed as follows: sn ct 15 sn ct + 34 sn + ct 33 sn + ct + 18 ¡hysical ¡roof of RecombinaPon • Barbara McClintock & Harriet Creighton, 1931 • Corn chromosomes with di¢erent morphologies • Must have some way of disPnguishing b/w the 2 homologues. • IdenP£able markers present at both ends of chromosome • CC & Cc = coloured; cc = colourless • WxWx & Wxwx = starchy endosperm; wxwx = waxy endosperm They look happy because they have corn chromosomes that they can physically disPnguish. Not covered in class; however you are responsible for this material 10/21/09 2 • CC & Cc = coloured; • cc = colourless • WxWx & Wxwx = starchy endosperm; • wxwx = waxy endosperm 1. 2a. 3. 2b. • From the progeny, we can infer the genotypes of the gametes produced by the individual with the 2 morphologically dis?nct chromosomes • Can then back up phenotypic observa?ons by looking at the chromosomes themselves; with recombinant phenotypes, saw recombinant chromosomes Linked Genes Happen to Autosomes too… • Parental types (combina¡ons) > recombinant types genes are LINKED • Parental allele combina¡ons transmifed together > 50% oF ¡me...
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- Fall '09
- Biology, Flowering plant, Ovule