fruit flies =| (1 Viewer)

[oranGez]

did morgan cross red eyed females + white eyed males.. or white eyed females and red eyed males? ive read/heard so many conflicting statements on this..

 

[withoutaface]

He crossed red eyed females with red eyed males and got 1/4 white eyed males from memory.

 

[elisabeth]

My understanding (R=red eyes, r=white eyes)

Once he found a white eyed male, he crossed it with a red eyed female. That gave all females as XRXr (heterozygous red eyes) and all males as XRY (red eyes).

Then he crossed one male and one female from those offspring. The results were:

25% female XRXR (homozygous red eyes)
25% female XRXr (heterozygous red eyes)
25% male XRY (red eyes)
25% male XrY (white eyes)

He then concluded that the genes for sex linked characteristics (here, the eye colour gene) were on the X chromosome.

 

[heyhey!]

morgan firstly crossed white eyed male with red eyed females.

What u guys needa understand, is that when he (later) crossed white eyed females with red eyed males he got very different results. IT IS THIS THAT LED HIM TO BELIEVE THAT IT WAS A SEX-LINKED trait.

does that make sense?

 

[*mel*]

morgan firstly crossed white eyed male with red eyed females.

What u guys needa understand, is that when he (later) crossed white eyed females with red eyed males he got very different results. IT IS THIS THAT LED HIM TO BELIEVE THAT IT WAS A SEX-LINKED trait.

does that make sense?

That's exactly right, because the white eyed female was only a result of later breeding. The white eyed male is more common because it is a trait on the X chromosome, therefore it needs only one affected chromosome to display the white eyes, as opposed to a white eyed female who would need two affected X chromosomes.

 

[Abtari]

FRUITFLY business!

did morgan cross red eyed females + white eyed males.. or white eyed females and red eyed males? ive read/heard so many conflicting statements on this..

It doesn't matter what you choose -red eyed or white eyed males, (or females) when you breed them for two successive generations, then you will still end up with a white-eyed male (provided that the red eyed organism is homozygous, i think). This is what i think anyway. I saw in a book once - there was a diagram with a white female and red male and the explanation of the diagram was talking about a red female and white male... but you end up with white eyed males in any case.

so no need to worry about these minor things. just stick to one that you find comfortable. the main thing to learn is that he found sex-linked traits in fruitflies.

actually, wait a minute - yea you get white males in any case, however if the grandfather fly was white-eyed then half of the males are white; if the grandfather fly was red-eyed then all of the males are white!

hope this helps. any corrections appreciated..

 

[lislabella]

It doesn't matter what you choose -red eyed or white eyed males, (or females) when you breed them for two successive generations, then you will still end up with a white-eyed male (provided that the red eyed organism is homozygous, i think).

if you breed a red eyed male with a female homozygous for red eyes...you will only produce offspring homozygous for red eyes...
XRY x XRXR
XRXR - 50%
XrXr - 50%

if the female is a carrier of the gene for white eyes...
XRY x XRXr
XRY - 50%
XRXr - 25%
XrY - 25%

 

[Abtari]

i wasn't talking about red eyed males and red eyed females crossing.

 

[lislabella]

nvamind i was just saying it does matter what you choose