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This one is too basic question:

I just came across $Ihh^{-/-}\ $ mouse. Is that means this mouse devoid of that gene Ihh. What is this sign called and are there other such representations?

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These are allele notations or nomenclatures and they refer to a gene, and what changes a particular gene has undergone, if any. In this case, the -/- refers to the fact that the Ihh gene is homozygous for a null mutation as correctly stated by @Alan Boyd. This page has further examples of allele nomenclatures. This page, which can be reached from the previous link provides comprehensive guidelines for nomenclature of genes, genetic markers, alleles, and mutations in mouse and rat. Please note that (if you look at the examples here) a nomenclature can be different in different species for example in the fly field, you tend not to use the -/- sign to denote a null mutation and instead it can be a name or a number for example Rab5(1). The only reason this is called allele 1 is that it shows the most severe phenotype, which is embryonic lethality. You can read this paper here for some of the Rab5 alleles produced in Drosophila.

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The IHH gene encodes the Indian hedgehog homolog protein, a member of the family of hedgehog proteins that regulates bone formation. The ihh-/- notation represents an animal which is homozygous for a null mutation in the gene (i.e. the animal has no functional IHH gene).

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  • $\begingroup$ Thanks. Can you add the other signs which are used? like for heterzygous it will be +/- or -/+. (Sorry, I know it's too basic.) $\endgroup$ – Devashish Das Aug 18 '14 at 19:09
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    $\begingroup$ @DevashishDas it's generally +/- for hets $\endgroup$ – MattDMo Aug 22 '14 at 0:34

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