MCQ - Independent assortment or Incomplete linkage

[Tyto alba]

Homework Statement

Two flies were crossed one wildtype another double mutant sepia(se) and vestigial(vg) yielding 40% wild type 40% se vg, 10% se and 10% vg. The genes show-

a.Complete linkage b.Incomplete linkage c.Independent assortment d. epistasis

2. The attempt at a solution
Since no. of combination of phenotypes appeared =/= 2 (there are non-parental traits so) it is not complete linkage.

It is neither epistasis because two genes controlling two diffrenet phenotypes not one.

It can be independent assortment or incomplete linkage.

Since the question says double mutant sepia(se) and vestigial(vg) (I am getting the idea that) that it is a female and the wildtype individual (with no genotype concerned hint it) is a male. The genes are likely on X chromosome.

So... it is incomplete linkage.

But I'm not sure why not independent assortment.

 

[epenguin]

Have you quoted the question completely? What do these results describe – an F2 generation?

 

[Tyto alba]

It is pretty much what was written. I'll share the snip-off :

I'm getting the idea of which one is male and which one's female, not the cross.

 

[Tyto alba]

Something just came to my mind.

An individual is homozygous recessive- the question may be indicative of test cross.

Besides if the other individual had been Homozygous dominant, there would have been just 1 phenotype in offsprings...so it is heterozygote.

Here, since the ratio deviates from 1:1:1:1 so the genes are not independently assorting and the only way to be able to display 4:1:1:4 ratio is to be present on same chromosome, and showing incomplete linkage-crossing over.

I have few questions:
1.Since the offsprings produced in one generation may have ratio other than 1:1:1:1 despite being on diff. chromosome/ far apart on the same chrom it would be due to complete chance that the the male gametes willl fuse with female gametes (hetero individual)to form an exact a 1:1:1:1 ratio. So questions like these are oversimplified ? And tests the concept ?
2. Is the reason as why no crossing over happens in male, known?
3. Could you shade some light as why the proportion of recombinants can never be more than 50% ? I think this would be true for both genes present on diff. chromosomes and same chromsome but part apart.

 

[epenguin]

Sorry I find this question hard to answer firstly because of the lack of any context (that's why I asked if this was all the information), secondly I'm not familiar with any of the special features of drosophila genetics (though I suspect they do not come into this question) and thirdly I find your logic hard to follow.

2. The attempt at a solution
Since no. of combination of phenotypes appeared =/= 2 (there are non-parental traits so) it is not complete linkage. OK

It is neither epistasis because two genes controlling two diffrenet phenotypes not one. I also do not see anything leading to suppose epistasis.

It can be independent assortment or incomplete linkage. As far as I understand independent assortment and non-linkage are practically the same thing aren't they?

Since the question says double mutant sepia(se) and vestigial(vg) (I am getting the idea that) that it is a female and the wildtype individual (with no genotype concerned hint it) is a male. The genes are likely on X chromosome.

So... it is incomplete linkage.

But I'm not sure why not independent assortment.

Something just came to my mind.

An individual is homozygous recessive- the question may be indicative of test cross. I don't know what this means

Besides if the other individual had been Homozygous dominant, there would have been just 1 phenotype in offsprings...so it is heterozygote. I think this is a key point. You cannot have these results in F1 if the parents are homozygous and there is dominance/recessivity. That's why I asked is this F2? But It appears from your current quote that it is F1. So you guess that there is heterozygosity. It seems slightly odd to me that this is in a problem about which you are given no information. It seems fairly reasonable to suspect that it is that form of 'heterozygosity' (termed hemizygosity) that constitutes maleness. Maybe this was your logic?.

Here, since the ratio deviates from 1:1:1:1 so the genes are not independently assorting and the only way to be able to display 4:1:1:4 ratio is to be present on same chromosome, and showing incomplete linkage-crossing over.

I have few questions:
1.Since the offsprings produced in one generation may have ratio other than 1:1:1:1 despite being on diff. chromosome/ far apart on the same chrom it would be due to complete chance that the the male gametes willl fuse with female gametes (hetero individual)to form an exact a 1:1:1:1 ratio. So questions like these are oversimplified ? And tests the concept ?
2. Is the reason as why no crossing over happens in male, known? I don't know but a quick google gave me this https://www.quora.com/Why-there-is-no-crossing-over-in-male-drosophila. Well that means something is known about what happens at the cellular level that is different from other organisms, not exactly why this has happened at evolutionary level.
3. Could you shade some light as why the proportion of recombinants can never be more than 50% ? With the given possibilities if having started as here with with (sp,vs) then later just 50% of the sp are also vs, it cannot be more random than that! But you could end up with less than half the sp being vs - that would be epitaxis. I think this would be true for both genes present on diff. chromosomes and same chromsome but part apart.

I think you need to set out your suppositions and argument more clearly to get any credit. However the question does not seem to me at all that will posed. I hope we can get some other contributions to this thread.

 

[Tyto alba]

Thank you for your attention.