Every individual has 2 copies of a gene (one from mom and one from dad). Positive hets have one normal (wild type) gene and one copy of the gene of interest. If you cross two positive hets and the trait is recessive then you will get 1/4 of the progeny with the desired trait. Of the remainder 2/3 =66% will be possible hets and the remaining 1/3 will have both dominant genes. The problem is that there is no way to tell which is which. If you cross an animal exhibiting the trait of interest (it will have both copy of desired gene) to a positive het, you will get 1/2 with the trait and all the rest should be positive het for that trait. Hope this helps.

Bob

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