Quiz 26: Developmental Genetics

The theory of evolution, as formulated by Darwin, is broadly based on two important principles both working at the species level and genetic level. The two important principles are: (i) genetic variation and (ii) natural selection. Genetic variation : This refers to the differences in the alleles of a gene that result in variations both within populations and among populations. At the species level, genetic variation is evident in the form of variation in phenotypes. For example Darwin observed that children resemble parents' more than unrelated people. At the genetic level, as we know, genetic variation involves differences in the alleles of a gene that can be caused by mutations. These mutations result in changes in the phenotypes that cause variations at the species level. Natural Selection : The concept of natural selection has its core centered on the theory of "survival of the fittest." According to this theory, only those species tend to dominate populations, who have the most favorable set of traits that allow them to survive the extreme and adverse conditions in an environment. Thus, this concept at the species level, results in either an increase or decrease in certain traits resulting in the emergence and survival of those phenotypes and genotypes, that help the population to survive the best. At the genetic level, those alleles that prove to be beneficial are inherited while those that are not useful or detrimental are not inherited ultimately leading to their elimination. This results in changes in the allele frequencies of a genE.

Since the populations of the snakes are separated by a physical barrier, thus there might be a possibility of reproductive isolation amongst them. Thus, some of the best ways to determine, if the two species of snakes are members of the same or different species, are: • Watching the two populations of snakes in nature, by sitting in a hidden spot, and observing if the eastern and western snakes interbreed in their natural environment. • The next step could be to breed them in captivity and observe if they mate with each other in captivity. • The best method of all would be to read and assess the chromosome structure and number for any differences present if any by karyotyping.

Evolution as a process has two stages: • The first stage is the stage of random mutations. In this stage, the population of a species might undergo various types of mutations depending upon the type of speciation or isolation that has acted upon it. For example, if a population of birds gets isolated by geographical barrier into four populations, then each population would develop random mutations depending on the environment conditions in their respective areas. Thus, the first step of evolution is a random process. • The second step of evolution is natural selection. In this stage, the nature plays its role in selecting the fittest of the lot. So in the above given example, of the four population of birds that have undergone random mutations, the nature will now select the ones that have the most beneficial mutations. So, the ones that have the least beneficial mutations or detrimental ones would be eliminated. Hence here, there is no role of randomness. Instead, it occurs slowly and in a manner that can explained for. Hence, this process of natural selection is not random. Thus, though the process of evolution includes random mutations, the evolution itself is not a random process as a whole.