You are studying development in a new species offruit fly,Drosophila mitensis, and you find a fly that has curly wings asseen here:
                                                          Â
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                                                                                                        CurlyWings                  Normal Wings
The Curly wings phenotype is due to a mutation at a singlelocus. Assume that you have flies that are true- breeding for thecurly wing phenotype(cur-cur-)and flies that are true-breeding for normal wings(cur+cur+).
·Propose a genetic cross todetermine whether the mutant phenotype is dominant or recessive,and list the genotype(s) of the F1 offspring you would obtain fromthis cross. Use cur- for the alleleassociated with curly wings and cur+for the allele associated with normal wings.
·What phenotype(s) would you expectto see in the F1 generation if the mutant phenotype is dominant? Inwhat proportion would you see these phenotypes?
·What phenotype(s) would you expectto see in the F1 generation if the mutant phenotype is recessive?In what proportion would you see these phenotypes?
You perform the experiment and find that the curly wingphenotype is recessive. A friend of yours has been studying amutation that causes short antenna. The short antenna phenotype isrecessive to the wild-type long antenna phenotype. You designatethat mutant allele (ant-) and thewild-type allele (ant+)
You set up the following crosses:
Curly wings, longantenna                                Normal wings, short antenna
Cross 1:Â Â Â Â Â Â Â Â Â cur-cur-ant+ant+Xcur+cur+ant-ant-
↓
F1:Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Normal wings,Long antenna
↓
Cross 2:      Normal wings, longantenna       X                    Curly wings, short antenna
                       (F1 from cross 1)
What type of cross is cross 2?
If the two genes are unlinked…
What phenotypic classes do you expect to see from cross 2 and inwhat ratios?
You perform cross 2, examine 1000 progeny and see that the genesare linked. In the table below, give the genotypes and phenotypesfor the parental and recombinant progeny.
Please note that you must use the following nomenclature. Usecur- andcur+ for the alleles of the wing gene.Use ant- andant+ for the alleles of the antennaegene.
| Number of progeny | Genotype | Phenotype |
Nonrecombinant | 431 + 429 | | |
| |
What is the recombination frequency between the wing and theantennae genes?
