Genetics Help!

[grayfalcon89]

Here is the question that I need help on. This is quite simple but my solution is, very very long, and I'm not sure whether I'm right or not.

You have a winged red-eyed fruit fly. Design a cross to determine whether the fly is heterozygous for either or both traits. Use a Punnett square to show all possible crosses.

[Auburngirl05]

You need to know red-eyed phenotype results from a dominant allele, and what the possible phenotypes are. Generally if you want to determine heterozygosity, you breed the organism with the unknown genotype with one that you know is homozygous recessive for whatever condition you're working with.

 

Edit: It's been a year since my last biology class, so someone please correct me if I'm wrong.

[grayfalcon89]

Okay. Here goes the answer that I have. If I write out the fruit fry's genotype, it would be either WW or Ww for the wing and RR or Rr for the red-eyed.

 

So, using some mathematics (yea right), I'll have four combinations, or cases to look for.

 

WWRR

WWRr

WwRR

WwRr

 

So, I test crossed them, meaning crossed with a fly with recessive trait on the both of its traits ---> wwrr.

 

Then, here is what I came up for the each of the case:

 

WWRR --> WwRr for all of its sixteen offsprings, therefore, it's homozygous dominant. Since no offspring with recessive alleles appeared.

 

WWRr --> WwRr and Wwrr. Each of them 8/16. So, for this case, it's homozygous for the wing since there was no recessive alleles on the wing but it will be heterozygous for eye color since recessive allels on the eye color occured. ---> rr --> recessive

 

WwRR ---> WwRr and wwRr. So, for this case, it's heterozygous for the wing since the recessive alleles on the wing occured. For the eye color, it would be homozygous since there was no recessive allels on the eye color.

 

WwRr ---> This case has 4/16 for WwRr, Wwrr, wwRr, wwrr. So, the unknown fly, for this case, will be homozygous for the both traits since the offspring with the recessive alleles occurred.

 

Here is one confusing part. Is the WwRr, a homozygous recessive? Because I know it's homozygous.. But I'm not sure whether it's call homozygous when there are four different kinds of possibilites.

 

And did I answer the question fully?

 

THANKS.

[grayfalcon89]

Um.. Is my concept right?

 

Only thing I really did on the school was just like one-factor cross or test cross on one trait but I've never done on two...

 

 

pretty sure I'm right.. though..

[Auburngirl05]

I'm pretty sure you've got the right idea with your crosses, although I'm no expert, but it looks like you've got the concept.

Here is one confusing part. Is the WwRr' date=' a homozygous recessive? Because I know it's homozygous.. But I'm not sure whether it's call homozygous when there are four different kinds of possibilites.

 

And did I answer the question fully?

 

THANKS. [/quote']

Traits are independent of each other (well, in most basic problems, in reality they're often linked, but I'm fairly certain this problem isn't intended to be that complicated). That means that a WwRr is heterozygous for both traits, but if it were Wwrr it would be heterozygous for the wing traits and homozygous recessive for the eye traits, it can be different for each pair of alleles.

 

I hope that answers your question, and yes, it seems like you have a good grasp of the test cross concept.