What do two different neutral isotopes of the same element have in common?

Which of the following examples can cause gene flow between populations? a.an increase in predators to a population of zebra b.a volcanic eruption that kills half of a population of mice c.bird droppings that contain seeds from a different location d.a person that sprays a toxin on a group of mosquitoes

During the process of two rails or sides break apart and attract new nucleotide bases to form a new and complete strand.

Why were the results whit just water so much different than the trials with the detergent ?