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Biology 334

1. Drosophila geneticists interested in the genes determining flying ability obtained three pure lines that were unable to fly. They called this flightless phenotype 'grounded' in contrast to the wild type 'flyer' phenotype. The three lines were called gounded 1, 2 and 3. They then performed the following analyses:

1. Grounded 1 x wild type -> F1 all flyers -> F2: 204 flyers, 68 grounded

2. Grounded 2 x wild type -> F1 all flyers -> F2: 268 flyers, 89 grounded

3. Grounded 3 x wild type -> F1 all flyers -> F2: 312 flyers, 105 grounded

4. Grounded 1 x grounded 2 -> F1 all flyers -> F2: 468 flyers, 364 grounded

5. Grounded 1 x grounded 3 -> F1 all grounded -> F2: all grounded

6. Grounded 2 x grounded 3 -> F1 all flyers -> F2: 819 flyers, 637 grounded.

a) Invent allele symbols, define them clearly, then write the full genotypes of the parents, F1 and F2 in all six analyses. (If your explanation involves more than one gene, make sure all the genes are represented in all genotypes in every cross.) [15 marks]

 

2. In the fungus Neurospora, a strain that was auxotrophic for thiamine (mutant allele t) was crossed to a strain that was auxotrophic for methionine (mutant allele m).  Linear asci were isolated and these were classified into the following groups.

 spore pair                                        ascus types                   

 1 and 2                                  t +    t+     t+       t+   tm    tm

 3 and 4                                  t+     tm    +m    ++    tm    ++ 

 5 and 6                                 +m    ++     t+      tm   ++    t+              

 7 and 8                                 +m    +m    +m   +m   ++   +m     

 number                                 260    76     4     54     1     5

(a) Determine the linkage relationships of these two genes to their centromere(s) and to each other.  Specify distances in map units.

 

(b) Draw diagrams to show the origin of each ascus type

 

(c) If 1000 randomly selected ascospores are plated on a plate of minimal medium, how many are expected to grow into colonies?

 

 

 

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