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mike.justice mike.justice
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11 years ago
GenotypeEePhenotype
EEEEeRed eyes
eEeeeWhite eyes

Is this right? If I get Ee + ee = recessive? and if I get EE and Ee I get dominant?
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irinairina
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11 years ago
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wrote...
11 years ago
There are a couple of problems here, I think. A test cross is ALWAYS a cross between something with the homozygous recessive. Test crosses are usually done to determine whether a fly with a dominant phenotype is homozygous dominant or heterozygous. So crossing A_ with aa will give you either all dominant phenotype (Aa) or half dominant (Aa) and half recessive (aa). These results will tell you whether the original fly was AA or Aa.

Now, white eye color in fruit flies is a sex-linked trait. So a male will either have red eyes (XE Y) or white eyes (Xe Y). Females can have red eyes (XE XE OR XE Xe) or white eyes (XeXe) .

A test cross of a heterozygous female (XE Xe) with a white eye male (Xe Y) will give half of each sex with red eyes and half of each sex with white eyes.
wrote...
11 years ago
Let me start over:  The cross EE x ee gives all Ee?
_____E__
e___Ee__? all heterozygous

The cross Ee x ee gives half dominant, half recessive:
_____E____e__
e___Ee___ee__
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