Heavy rains and mudslides cause a river to change course, isolating two groups of lizards from one another. if they remain isolated for a long period of time,

If they remain isolated for a long period of time, the two groups will probably diverge genetically, and may result in speciation.

Genetic divergence is the process whereby two groups of the same ancestral species acquire autonomous genetic changes through time, usually after the groups have been separated reproductively for some period of time.

Speciation is an evolutionary process whereby populations develop to become different species.

a tetrad is the foursome during meiosis made by two homologous chromosomes that have each already replicated into a pair of sister chromatids.

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i guess you forgot putting it.