In any event, there appears to be a motif dependant correlation between repeat length and multi-step mutation change for SSR loci.
We also tested all loci for neutrality using the program LOSITAN using a multi-step mutation model and 10,000 replicates of data collection [ 52, 53].
These lines might reflect real multi-step mutations but they might also have fixed multiple single repeat mutations.
Several lines exhibited multiple step changes from the progenitor sequence, although it is unclear whether these are multi-step mutations or multiple single step mutations.
As a proportion of other than one-step mutations (p g ) five different values were used: 0.00, 0.05, 0.10, 0.20 and 0.30 and the mean size of multi-step mutations (δ g ) was set to 3.1 (see [ 48]).
Furthermore, researchers have shown that the directionality of multi-step mutations is length-dependent with a critical repeat number at which contractions are more frequent than expansions [ 26], while others suggest that a critical number does not exist [ 27].
The two phase model of DiRienzo et al. (1994) is a modification of the SMM with most mutations involving a gain or loss of a single repeat and the remainder of the mutations being multi-step mutations following a geometric distribution.
This was previously a multi step process.
In a model of multi-step carcinogenesis, mutations of the Deleted in Colon Cancer (DCC) and the p53 tumor suppressor genes with functional abnormalities of the proteins they encode may be involved in the development of a variety of tumors [ 1].
This study further supports the notion that cancer development and progression is a multi-step process and mutation of two or more genes may be required for cell transformation in mammary epithelial cells.
Likewise, in mouse models used to study the combined action of multiple genes in cancer, the genes of interest are usually simultaneously mutated, whereas "natural" tumours progress through a multi-step process, where mutations are gradually acquired.
