## genetic crossing why isnt it 1/4 :(

Genetics as it applies to evolution, molecular biology, and medical aspects.

biohelp22
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### genetic crossing why isnt it 1/4 :(

this question has confuzzled me

in humans, if red hair (R) is dominant to brown hair (r) and freckles (F) are dominant to no freckles (f) what fraction of the progeny cross RrFf x RRff will have red hair and no freckles??

a. 9/16
b. 1/2
c. 3/8
d. 3/16
e. 1/16

i did the punnett square and i got 4/16

d00d
Garter
Posts: 23
Joined: Sun Apr 23, 2006 5:38 pm
Parents: Genotype- RrFf x RRff

Meiosis: Gametes- (RF Rf rF rf) x (Rf Rf Rf Rf)

Offspring: Genotypes- 4 RRFf, 4 RRff, 4 RrFf, 4 Rrff

Phenotypes- 8 Red Haired, No Freckles

therefore you have a possible 8 out of 16 with red hair and no freckles which amounts to a probability of 1/2. the answer is B.

sdekivit
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Location: holland
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### Re: genetic crossing why isnt it 1/4 :(

biohelp22 wrote:this question has confuzzled me

in humans, if red hair (R) is dominant to brown hair (r) and freckles (F) are dominant to no freckles (f) what fraction of the progeny cross RrFf x RRff will have red hair and no freckles??

a. 9/16
b. 1/2
c. 3/8
d. 3/16
e. 1/16

i did the punnett square and i got 4/16

red hair and no freckles = RRff or Rrff

chance for RR = 1/2 and ff = 1/2 --> RRff = 1/2 * 1/2 = 1/4
chance for Rr = 1/2 and for ff = 1/2 --> Rrff = 1/2 * 1/2 = 1/4

combined chance for red hair and no freckles: 1/4 + 1/4 = 1/2

d00d
Garter
Posts: 23
Joined: Sun Apr 23, 2006 5:38 pm
thanks for repeating!
Since when did what we pay for coloured cloth gauge our gravity?

sdekivit
King Cobra
Posts: 586
Joined: Sat Jul 30, 2005 7:16 pm
Location: holland
Contact:
d00d wrote:thanks for repeating!

i didn't repeat you

--> i gave another method, which is much faster, because you don't have to draw a punnett square

d00d
Garter
Posts: 23
Joined: Sun Apr 23, 2006 5:38 pm
i take that back...sorry there man.
Since when did what we pay for coloured cloth gauge our gravity?

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