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I have been known to do that, but you should provide more info if you want an answer to your question... :D
okay, so its a lab called "genetics of drosophila". The parents were red eyed male vestigial and white eyed female with normal wings. the f1 generation loooked like this:
If we counted 200 flies for the f2 generation, what could be an expected ratio for the genotypes?
All the f1 flies have red eyes, so you know that the red eye color allele is dominant to the white eye color allele. You also know that the red eyed parent must have been homozygous dominant and the white eyed parent must have been homozygous recessive. Are you clear on why?
yes. so all the children must have red eyes, but some have vestigial wings and some do not right?
Ahh, I'm talking about the parents for the moment, not the offspring. Is it clear to you why the red eyed fly must have been homozygous dominant for the eye color allele and the white eyed fly must have been homozygous recessive for the eye color allele?
Cool. Onto wings. Most of the flies have normal wings; a very small number of flies have vestigial wings. So it should be obvious that the normal allele is dominant to the vestigial allele. All the offspring with the vestigial phenotype are homozygous recessive and the other flies could be either heterozygous or homozygous dominant. Clear?
What is the only combination of parental genotypes which could produce this F1 distribution?
red eyed male vestigial and white eyed female with normal wings
No, parental genotypes, not parental phenotypes.
ohh sorry. RRnn and rrNN or rrNn? if R - red eyes N-normal wings r-White eyes n -vestigial
You have the eye color genes right. The red eyed fly is RR and the white eyed fly is rr. But if you look at the wing genotypes, NN x Nn will give all offspring a dominant phenotype. A couple of the offspring have the nn phenotype...
ohh does that make it sex linked trait then?
wait im so stupid.
RRnn x rrNn RRnn x rrNN
RRnn x rrNN would require all the offspring to be Nn for the wing trait. If that were the case all the flies would have normal wings. RRnn x rrNn would require that roughly half the offspring would be Nn and have the dominant phenotype and half the offspring would be nn and have vestigial wings. You don't see that, either...
Now I do.
No, almost all the flies have normal wings. But a couple have vestigial wings. And where did the info on the f1 generation go?
it was 11 red/normal female 7 red/normal male 1 red/vestigial female 1 red/vestigial male
And what do you think the parent's genotypes were for the wing gene?
well it has to be nn and Nn or NN doesnt it?
Yes. Both parents can be any one of those three...
well i know one parent is definitely RRnn
Does it say you have a vestigial winged parent? Sorry if you already said that, but some info got deleted somehow...
yeahh it is a vestigial winged parent with red eyes. its okay, thanks for taking the time to help me
That does not make much sense in light of the observed ratios of the offspring. I thought it would have to be a Nn x Nn. Unless most of the vestigial winged offspring die before they are born. For nn x Nn, which is the only option to Nn x Nn, you'd expect 1/2 normal and 1/2 vestigial... It does not make much sense at all. Is this real data from a real fly cross, or data that you were given as part of a prelab?
A real fly cross that we did. The data is our own, we counted it.
Oh, that is interesting. You have quite a few of your vestigial winged flies dying before they are born because you would expect to see 1/2 normal and 1/2 vestigial. |dw:1332987649638:dw| That changes the rules of the game a little.
ohh i see why you said that. Yes I understood, but the results are quite the opposite