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oakrueangsit oakrueangsit
wrote...
Posts: 59
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12 years ago
C-curly antennae
c-straight antennae
S-spotted wings
s-no spots on wings

Could you tell me the difference between the genotypic and phenotypic ratios for a dihybrid cross if the first question is too much?
thanks
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2 Replies
OAK

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wrote...
12 years ago
Genotype means what the actual genetic composition is (so, ccSS or CcSs or CCss, etc) - phenotypic ratio is talking about what the APPEARANCE is - so CCss (curly non spotted) would be phenotypically the same as Ccss and CCSS (curly spotted) would be phenotypically the same as CcSs, CCSs, CcSS, etc.

This cross should give you a phenotype ratio of 9:2:2:1 with 9 curly spotted, 2 straight spotted, 2 curly non spotted and 1 straight non spotted.
The genotypes would be more varied - you can get those by setting up a punnett square.
Not doing that for you Face with Stuck-out Tongue

**EDIT: Sorry; messed up my math at first - note corrected ratio.

And as a result set up the punnett square to double check so here are your genotypes:
---------CS--------Cs-------cS-------cs
CS |  CCSS | CCSs | CcSS | CcSs
Cs  |  CCSs |  CCss | CCSs | Ccss
cS  |  CcSS |  CcSs |  ccSS |  ccSs
cs   |  CcSs |  Ccss  |  ccSs  | ccss

So:
CCSS: 1
CcSs: 3
ccSs: 2
ccSS: 2
Ccss: 2
CcSS: 2
CCSs: 3
ccss: 1
wrote...
12 years ago
The genotypic ratio of this cross would be:
1 - CCSS
2 - CCSs
2 - CcSS
4 - CcSs
1 - CCss
2 - Ccss
1 - ccSS
2 - ccSs
1 - ccss
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