Molecular clocks use rates of mutation to measure evolutionary time.Mutations add up at a fairly constant rate in the DNA of species that evolved from a common ancestor. The more mutations that happened in each lineage, the greater is the differences between these lineages.
A cell can only respond to signals from other cells, not from the physical environment. receptor activation. The ability of a specific tissue or organ to respond to the presence of a hormone is dependent on: the presence of the appropriate receptors on the cells of the target tissue or organ.
This is why natural selection acts on phenotypes instead of genotypes. A phenotype is an organism's physical traits, while a genotype is an organism's genetic makeup. This may sound counter-intuitive since the genetic makeup does get<span> passed on from generation to generation through reproduction.</span>
