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Title: test cross: Biology/Genetics? Post by: mike.justice on Sep 6, 2012 GenotypeEePhenotype
EEEEeRed eyes eEeeeWhite eyes Is this right? If I get Ee + ee = recessive? and if I get EE and Ee I get dominant? Title: test cross: Biology/Genetics? Post by: irina on Sep 6, 2012 Content hidden
Title: test cross: Biology/Genetics? Post by: ilkat on Sep 6, 2012 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. Title: test cross: Biology/Genetics? Post by: davesf4i on Sep 6, 2012 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__ |