Genetic Probability ???

[MichaelXY]

Perhaps someone might not mind explaining to me how this works.

Say we have a multiple trait mix of ---> ppYyrr

We get pp = 1/4 , I get that
Yy = 1/2 , get that too
rr = 1/2 , WTH? How is rr different than pp?

I guess I should make the punnett square, but I should also be able to figure this out using math. I do not understand why pp and rr are not the same.

Thanks

[mith]

Parent 1 is rR
Parent 2 is rr

[MichaelXY]

Thanks Mith. I see it now, I did a P- square. Is it safe to say, odd combos = 1/2 and even combos = 1/4, By even and odd I mean, (even -->Pp x Pp= 1/4) (odd --> Pp x pp = 1/2).

[MichaelXY]

Just when I think I am getting it, I discover I am not.

I have this question:

Feather color in budgies is determined by two different genes Y and B. YYBB,YyBB or YYBb is green; yyBB or yyBb is blue; YYbb or Yybb is yellow; and yybb is white.

Two blue budgies were crossed. Over the years, they produced 22 offspring, 5 of which were white. What are the most likely genotypes for the two blue budgies?

Choices are:
A. yyBb and yybb
B. yyBB and yybb
C. yyBB and yyBb
D. yyBB and yyBB
E. yyBb and yyBb
Answer is E. yyBb and yyBb
Since white is yybb, I can eliminate B,C,D, but leaves A and E. My teacher said I should be able to find the answer just by looking at it, but I don't. How would one approach this problem? I know, probably seems obvious to a lot of you, but Mendel stuff has me going crazy.
And I am looking for solution that does not involve Punnet square.
-------------------------Edit----------------------------------------------------
Ok, I think I just figure it out. 22/5 = 4.4 or 1/4 or so. BbxBb = 1/4. Is that that way to solve it?

[MrMistery]

No, it is obvious actually, your prof is right.
The two need to be blue, so you can cross out A and B, because yybb is white.
yyBB and yyBb will produce offspring yyBB and yyBb, none of the white. Cross out C.
yyBB and yyBB will produce yyBB offspring, which is not white. Cross out D.
yyBb and yyBb will produce offspring yyBB, yyBb and yybb. yybb is white, so there is your answer.
It doesn't matter that 5 out of 22 are white, the numbers are too small to draw conclusions anyway. They are just there to confuse you.

By the way, i worked out the gene relationship, which is kinda cool.
yybb does not have any dominant allele and does not produce any functional protein.
YYbb or Yybb have one dominant Y allele, which codes for the enzyme that makes the yellow pigment.
yyBb or yyBB have one dominant B allele, which codes for the enzyme that makes the blue pigment.
YYBB, YYBb, YyBB or YyBb have both dominant alleles, and have both the yellow and blue pigment. As we know from painting blue+yellow=green.

Cheers

[MichaelXY]

Your one smart guy. Mulţumesc Mistery

[MrMistery]

No prob.
By the way, did you look that up or did you know it in advance?

[MichaelXY]

I have to be honest, I googled thank you in Romanian.