How does our modern classification system show the evolutionary relationship among organisms?

The individuals having characters best adapted to the surroundings are able to survive. Their characters, that is, the genes present in them, pass on to the further generations. Biological evolution is basically, change in living organisms over a long period of time. Evolutionary theory states that different types of living organisms originate from common ancestor due to modifications in successive generations.

All living organisms show variation in characters. Biological classification is arrangement of living organisms into groups based on similarities and differences observed among them. The smallest group or taxon is species which consists of individuals which can successfully reproduce with each other. It is observed that, generally, the organisms having close evolutionary relationship are placed together in a smaller taxon. As we go to higher taxon, the relatedness decreases. This is consistent with the evolutionary theory. Therefore classification helps to establish evolutionary relationship.

fertilization, pictured in figure 24.23a is the process in which gametes (an egg and sperm) fuse to form a zygote. the egg and sperm each contain one set of chromosomes. to ensure that the offspring has only one complete diploid set of chromosomes, only one sperm must fuse with one egg. in mammals, the egg is protected by a layer of extracellular matrix consisting mainly of glycoproteins called the zona pellucida. when a sperm binds to the zona pellucida, a series of biochemical events, called the acrosomal reactions, take place. in placental mammals, the acrosome contains digestive enzymes that initiate the degradation of the glycoprotein matrix protecting the egg and allowing the sperm plasma membrane to fuse with the egg plasma membrane, as illustrated in figure 24.23b. the fusion of these two membranes creates an opening through which the sperm nucleus is transferred into the ovum. the nuclear membranes of the egg and sperm break down and the two haploid genomes condense to form a diploid genome.

explanation: