The experiment started with 1 white eyed female(WEF)and 1 red eyed
male(REM)in the P1 generation, the P2 generation had 5 red eyed
females(REF) and 1 white eyed male(WEM).After 3 weeks there are 47
REF,42 WEF,31 REM,and 31 WEM in the F2 generation. I need punnet
squares for each generation and a chi square with statistics, with an
explanation for the outcome in genetics vocabulary.

Hello and thank you for your question.

There is an automated program on the Internet called Virtual Fly Lab
http://biologylab.awlonline.com/login.php?labname=FlyLab&labdir=FlyLab&labcode=FLY
that handles these calculations automatically.  It requires an access
Code that I do not have, so in this answer I have calculated
everything manually.

A key fact in this calculation is that in Drosophila, the eye-color
gene ‘white’ is sex-linked. White eye is recessive, red eye is
dominant.
http://fp.bio.utk.edu/botany/Botany_courses/fpcourses/240%20genetics/Practice%20Final.htm
So using "R" for the dominant red eye gene and "r" for the recessive
white eye gene, you know the REM red eyed male's genes are all [XR Y]
and the WEF white eyed female's genes must be [Xr Xr].

Are you with me so far?  Males are always XY and so a REM's sole X
chromosome must have the R gene riding on it.  Females are always XX
and for her to have white eyes, because it is recessive, both of a
WEF's X chromosomes must have the r gene riding on them.

Now we can draw the Punnett Square for the cross of the first
generation that produces the second generation--I put the male on top
of the box and the female on the left side:

                 XR      Y
                 _____________
          
           Xr  /  XRXr    XrY

           Xr  /  XRXr    XrY

This is an easy one to call, because you can see that all the female
offspring will be XRXr (red eyed females REF because red is dominant,
and they're all heterozygous) and all the male offspring will be XrY
(white eyed males WEM because they only have the Xr gene for eye
color).

And it matches your data; thanks to the Punnett Square we also know
the genotype of each as given above).

For the crossing of the second generation that produces our third
generation, here's the Punnett Square:


                 Xr      Y
                 _____________
          
           XR  /  XRXr    XRY

           Xr  /  XrXr    XrY

So the prediction for the third generation is 25% REF [heterozygous
XRXr], 25% WEF [homozygous XrXr], 25% REM [XRY] and 25% WEM [XrY].

But your experiment produced 47 REF,42 WEF, 31 REM,and 31 WEM instead
of the predicted 38 or so of each.

So we need to apply chi squared so we can compare your result to the
critical value.
You can review the Chi square calculation method at
http://old.jccc.net/~pdecell/bio205/hyptest1.html

Phenotype Observed#(Oi) Expected#(Ei)	chi-square 
				         (Oi -Ei)^2/Ei
REF	47		37.75	2.267
WEF	42		37.75	0.478
REM	31		37.75	1.207
WEM	31		37.75	1.207
sum	151			5.159


The column on the right calculates the observed chi-square statistic,
which is a sum of the 4 values at the end of each row (Oi -Ei)^2/Ei
[Google isn't very good at laying out tables.  In the first row 2.267
should be under the heading 'chi-square' determined because that's the
value of
(47-37.75)^2/37.75]
 
Since there are 4 rows, there are 3 degrees of freedom, and a
chi-squared table will tell you that the
critical chi-square value (alpha = 0.05; df = 3)is 7.81

The observed Chi square, 5.159, is less than the critical chi square
(c 2 3 df = 7.81) at the 0.05 level of significance. Thus the
hypothesis that the genes are unlinked is accepted.

For a further discussion of how gene linking produces results
different from the Punnett Square predicion, take a look at
http://old.jccc.net/~pdecell/transgenetics/linkage.html

But in your case, the observations were not so far away from the
prediction, so you can consider your results consistent with what the
Punnett Square foretold.

Google search terms used:
chi punnett fly eye


Thank you again for giving me the chance to review this for you.

Sincerely,
Google Answers Researcher
Richard-ga

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Request for Answer Clarification by bettjay-ga on 27 Apr 2003 09:32 PDT

I'm not sure of the ratio of the punnet square, shouldn't it read
1:2:3:4:, I'm confused? Please clarify.

---

Request for Answer Clarification by bettjay-ga on 27 Apr 2003 10:58 PDT

Richard, also when you did the punnett square, you used X and Y. In
class we only used R and r, so your combination has me confused. Could
you change it? I'm 53 and taking college biology, this is kicking my
butt. Thanks

---

Clarification of Answer by richard-ga on 27 Apr 2003 13:40 PDT

Hello again.

You asked:
"I'm not sure of the ratio of the punnet square, shouldn't it read
1:2:3:4:, I'm confused? Please clarify."
You're right each square has four boxes, so there are potentially 4
outcomes, 25% each.
In the first square, those outcomes are
XRXr    XrY 
XRXr    XrY 
So you could say 25% female XRXr; 25% female XRXr; 25% male XrY; 25%
male XrY.  In my answer I added the two like pairs together for 50%
female XrXr and 50% male XrY.

In the second square, those outcomes are
XRXr    XRY 
XrXr    XrY 
(25% female XRXr; 25% female XrXr; 25% male XRY; 25% male Xr)

You also asked:
"when you did the punnett square, you used X and Y. In
class we only used R and r, so your combination has me confused. Could
you change it?"
It certainly is important who's male and who's female because the
genders are given as part of the question, and eye color is
sex-linked, meaning the chromosome for eye color rides on the X
chromosome of which females have two and males have one.
The best I can do is rewrite the first square as:
                         MALE 
                    R             -- 
                 ____________________ 
           
           r  /  female Rr    male r 
 FEMALE
           r  /  female Rr    male r

and rewrite the second square as:
                         MALE 
                    r             -- 
                 ____________________ 
           
           R  /  female Rr    male R 
 FEMALE
           r  /  female rr    male r

It's because the eye color gene resides on the X chromosome that the
male has only a single chromosome for eye color; and if we can't write
the Y we just have to leave a "--" meaning no eye color gene on the
male's Y chromosome.

Does that help?
-Richard

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Request for Answer Clarification by bettjay-ga on 27 Apr 2003 19:22 PDT

Richard, just 1 more thing and I will be finished. Can you think of a
good scientific title for this paper? It should include the primary
factor studied, the outcome or effects, and organism studied. An
example: The Effect of Varying Serotonin Concentrations on Ca++
Release At Synaptic Membranes in MKotoneuron of Aplasia.
Mind-bogling!!! If you can think of a good title there is a great tip
and I'll close up with a great review. Thanks

---

Clarification of Answer by richard-ga on 27 Apr 2003 20:05 PDT

I like
"Sex-Linked Inheritance of the Gene for White Eye in Drosophila
melanogaster"

But if you want it a little more involved, you could say

"Proof of Sex-Linked Inheritance of the Gene for White Eye in
Drosophila melanogaster"

or even

"An Investigation of the Transmission of the Gene for White Eye in
Drosophila melanogaster via Sex-Linked Inheritance from a Mutant
Female Phenotype"

Good luck and thanks again for letting me help with your project!
Richard-ga

Richard did a great job, clarified everything and made it easy to
understand. Thanks for a job well done!!!!

bettjay
Thank you for the kind words, rating and generous tip!
I'm glad you found our service helpful
Richard-ga