Question

anyone here do a lab breeding fruit flies?

Answer 1

I have been known to do that, but you should provide more info if you want an answer to your question... :D

Answer 2

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:

Answer 3

If we counted 200 flies for the f2 generation, what could be an expected ratio for the genotypes?

Answer 4

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?

Answer 5

yes. so all the children must have red eyes, but some have vestigial wings and some do not right?

Answer 6

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?

Answer 7

yes

Answer 8

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?

Answer 9

Yes!

Answer 10

What is the only combination of parental genotypes which could produce this F1 distribution?

Answer 11

red eyed male vestigial and white eyed female with normal wings

Answer 12

No, parental genotypes, not parental phenotypes.

Answer 13

ohh sorry. RRnn and rrNN or rrNn?
if R - red eyes N-normal wings
r-White eyes n -vestigial

Answer 14

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...

Answer 15

ohh does that make it sex linked trait then?

Answer 16

wait im so stupid.

Answer 17

RRnn x rrNn
RRnn x rrNN

Answer 18

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...

Answer 19

Now I do.

Answer 20

No, almost all the flies have normal wings. But a couple have vestigial wings. And where did the info on the f1 generation go?

Answer 21

it was 11 red/normal female 7 red/normal male
1 red/vestigial female 1 red/vestigial male

Answer 22

And what do you think the parent's genotypes were for the wing gene?

Answer 23

well it has to be nn and Nn or NN doesnt it?

Answer 24

Yes. Both parents can be any one of those three...

Answer 25

well i know one parent is definitely RRnn

Answer 26

Does it say you have a vestigial winged parent? Sorry if you already said that, but some info got deleted somehow...

Answer 27

yeahh it is a vestigial winged parent with red eyes. its okay, thanks for taking the time to help me

Answer 28

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?

Answer 29

A real fly cross that we did. The data is our own, we counted it.

Answer 30

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.



That changes the rules of the game a little.