st + bw testcross drosophila melanogaster

[lucashell]

Hey I am doing a school project using Drosophila strains of scarlet female and brown male mutant test cross to detect mutation in either chromosome 2 or 3. I am going to feed the male with the mutagen however i have some questions .

1)Why mutagens are feed to male ? Is it because males have only one copy of the X-chromosome while
females have two copies have two X-chromosomes. As males are hemizygous for all X-linked
genes, they will express the phenotype of all X-linked recessive mutations that they carry.
Females are diploid for X-linked genes and express phenotypes of X-linked recessvie mutations
only when they are homozygous.

2) I should put how many males and females in one vial ?
1 male 2 females ? 2 males 2females ?
If I use 1 male i am afraid it will die but if i use 2 male and there is a mutation how will i know mutation occurs in which male ?

3) How do I interpret the results ?
If its 9:3:3:1 its normal
what if the ratio of brown n scarlet is 1:1 ? and other weird ratio ?

4) If there is mutation and i mapped it to either chromosome 2 or 3 what is the significance of such a result and how do I extrapolate it to humans ?

Any additional thoughts and suggestion are highly welcomed !!!!!!!!!

 

[Hercules Rockefeller]

1)Why mutagens are feed to male?

Because males produce lots of sperm from many spermatogonial cells whereas females produce (relatively) only a few ova. The many spermatogonial cells in males present multiple targets for the mutagen whereas there are fewer oogonial targets in females. At least, that’s the reasoning behind vertebrate mutagenesis; I suppose it also holds true for invertebrates as well.

So, the object is to introduce mutations into the spermatogonia of the males. When this occurs, the sperm that arise from the mutagenized spermatogonia will be carrying the mutations. Thus, these males can be used to cross with multiple different females in order to establish F1 lines for subsequent mutant screening.

2) I should put how many males and females in one vial ?

I don’t know. You will have to ask someone with specific experience in Drosophila experiments.

3) How do I interpret the results ?
If its 9:3:3:1 its normal
what if the ratio of brown n scarlet is 1:1 ? and other weird ratio ?

The 9:3:3:1 ratio is what you see for a test cross involving two unlinked loci. A 1:1 ratio is what you see for linked loci with a small number of recombinant variants due to crossing over.

Of course, these are the predicted ratios. In reality you always get “weird ratios”. Your job is to apply statistical analysis (eg. chi[sup]2[/sup] test) to determine whether the observed ratios differ from the expected ratios by chance alone.

4) If there is mutation and i mapped it to either chromosome 2 or 3 what is the significance of such a result and how do I extrapolate it to humans ?

What do you mean? You will have to be more specific. If you are trying to relate the genetics of Drosophila eye colour to humans then there is a similarity in the sense that humans also have genes that control eye pigmentation with some being dominant over others.

 

[lucashell]

Thank You !!!!!

First of all A BIG THANK YOU for those that have replied to my post !!!!! the information you guys give are valuable !!!!

 

[lucashell]

Qns AGAIN !!!!!

1) If a mutagen causes a mutation in the eye colour of drosophila, will it cause a more serious effects on human other than the eye colour ?

2) What are the constraints of doing a scarlet + brown cross ?