Drosophila cross Flashcards
What are 4 advantages of studying drosophila genetics?
1) Short life cycle with 10 days from egg to adult
2) Grown easily in lab
3) High fertility where a single gamete can have over 400 progeny
4) Genetically well-characterised with a large number of mutant strains available
How can you tell a drosophila is male?
There is a dark tip to their abdomen visible from their underside
They are smaller
In our cross what was strain A and strain B?
strain A: Homozygous for white-eye (w) and vestigial short wings (vg)
strain B: wild type ie. red eyes, normal wings
Why do you have to immobilise the drosophila?
To score the phenotypes and set up the mating tubes
How do you immobilise them?
CO2 then use paintbrush to move them
How many males and females did we use to make the F2?
8 of each
Why can’t you use females from the F1 tubes for the backcrosses?
Need virgin females, have to get them from separate tubes
What did our cross between A and B show?
White eye is recessive to red eye
Vestigial wings are recessive to normal wings
White eye gene is sex linked and located on the x chromosome
Vestigial wing gene is autosomal so shows no linkage
How can you predict phenotype and genotype of offspring?
What were our expected ratios for female and male offspring when we crossed the F1 with each other?
With a Punnet square
(see notes for diagram)
Female and male : both expect 3(+ +) : 1 (+ vg) : 3 (w +) : 1 (w vg)
What was an unexpected issue with our practical results and why did this happen?
Vestigial mutants were seriously under-represented
These flies are less viable than Wild type counterparts and more likely to be trampled into their food and die
What were some potential issues with the cross?
1) White-eyes flies emerge later than their WT counterparts so could be underrepresented among progeny
2) Crumpled/wet wings could be confused with the vestigial phenotype
3) Immature females could look like males
