Over the last several decades, the scientific community has gathered a large amount of information regarding genetics and genetic variation. what are two main sources that lead to increased genetic variation?

selective breeding

gamete mutations

recombination

genetic drift

i have looked all in my notes and can't find anything on this topic.

The two main sources that lead to increased genetic variation are gamete mutations and recombination.
A gamete is the cell which combines with another cell during fertilization. So, its mutation can lead to variation in genes. Recombination as well, as the position of genes is changed.

The type of rock she find is a sediment rock

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