48. Consider a bacterial population where some individuals have a gene for resistance to a particular heavy metal. If this population is introduced into an environment contaminated with that heavy metal, what would happen according to natural selection?

All bacteria would develop resistance through continuous exposure.
The non-resistant bacteria would acquire resistance and pass it on.
The resistant bacteria would survive and reproduce more, increasing the frequency of the resistance gene.
The heavy metal would directly mutate non-resistant bacteria into resistant ones.

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