Download CBSE Class 12 Biology Evolution Notes Set A in PDF format. All Revision notes for Class 12 Biology have been designed as per the latest syllabus and updated chapters given in your textbook for Biology in Standard 12. Our teachers have designed these concept notes for the benefit of Grade 12 students. You should use these chapter wise notes for revision on daily basis. These study notes can also be used for learning each chapter and its important and difficult topics or revision just before your exams to help you get better scores in upcoming examinations, You can also use Printable notes for Class 12 Biology for faster revision of difficult topics and get higher rank. After reading these notes also refer to MCQ questions for Class 12 Biology given our website
Evolution Class 12 Biology Revision Notes
Class 12 Biology students should refer to the following concepts and notes for Evolution in standard 12. These exam notes for Grade 12 Biology will be very useful for upcoming class tests and examinations and help you to score good marks
Evolution Notes Class 12 Biology
Evolution: Process that results in heritable changes in a population spread over many generations (change in allele frequencies over time) leading to diversity of organisms on earth. It is the genetic change in a population or species over generations (Genes mutate, individuals are selected, and populations evolve).
Evidences of evolution:
From comparative anatomy: Comparison of body structures amongst different species comes under comparative anatomy. Certain anatomical similarities among species bear witness to evolutionary history. eg. the same skeletal elements make up the forelimbs of man, horse, whale and bat, but each of them perform different functions. However, structural similarities in all mammals descended from a common ancestory with prototype forelimbs are common suggesting homology. Comparative anatomy confirms that evolution is a remodeling process. Ancestral structures that originally functioned in one capacity become modified as they take on new functions-‘descent with modification’.
Adaptive radiation or mega evolution: Diversification, over evolutionary time, of a species or group of species into several different species or subspecies that are typically adapted to different ecological Group of organisms diversify greatly and take on new ecological roles. (for example, Darwin's finches in the Galapagos Island and Marsupials in Australia).
Allopatric speciation:or geographic speciation is speciation that occurs when biological populations of the same species become vicariant or permutable— isolated from each other to an extent that prevents or interferes with genetic interchange. Can be the result of population dispersal leading to emigration, or by geographical changes such as mountain formation, islandformation, or large scale human activities (for example agricultural and civil engineering developments).
Artificial selection: Process by which humans breed animals and cultivate crops to ensure that future generations have specific desirable characteristics.(In artificial selection, breeders select the most desirable variants in a plant or animal population and selectively breed them with other desirable individuals).
Atavism or reversion: the reappearance of those ancestral characteristics in an organism or in the organisms of a group, which do not occur normally or which represent the reminiscent of normal structures possessed by the individuals of other groups. Examples - human baby born with tail etc.
Big bang theory: States that the universe began in a state of compression to infinite density, and that in one instant all matter and energy began expanding and have continued expanding ever since.
Biological Evolution: In the early 1800s French naturalist Jean Baptiste Lamarck suggested that evolution is a process of adaptation, the refinement of characteristics that equip organisms to perform successfully in their environment. However, unfortunately we remember Lamarck for his erroneous view of how adaptation evolved (the inheritance of acquired characters). Branching descent and natural selection are the two key concepts of Darwinian Theory of evolution. According to him all the species inhabiting earth today descended from ancestral species (descent with modification) and natural selection is the mechanism for such descent with modification. Natural Selection states that a population of organisms can change over the generations if individuals having certain heritable traits leave more offspring than other individuals, resulting in a change in the populations genetic composition over time.
Convergent Evolution: Convergent evolution takes place when species of different ancestry begin to share analogous traits because of a shared environment or other selection pressure. For example, whales and fish have some similar characteristics since both had to evolve methods of moving through the same medium: water.
Darwin’s finches: Divergent Evolution: Evolutionary pattern in which two species gradually become increasingly different. This type of evolution often occurs when closely related species diversify to new habitats. On a large scale, divergent evolution is responsible for the creation of the current diversity of life on earth from the first living cells. On a smaller scale, it is responsible for the evolution of humans and apes from a common primate ancestor. Adaptive radiation is one example of divergent evolution.
Directional selection shifts the overall makeup of the population by favoring variants of one extreme within a population. Natural selection may be directional: it may favor, for example, smaller individuals and will, if the character is inherited, produce a decrease in average body size. Directional selection could, of course, also produce an evolutionary increase in body size if larger individuals had higher fitness.
Disruptive selection, like directional selection, favors the variants of opposite extremes over intermediate individuals. Disruptive selection differs in that sudden changes in the environment creates a sudden force favoring that. In nature, sexual dimorphism is probably a common example.
Founder Effect: A cause of genetic drift attributable to colonization by a limited number of individuals from a parent population. When few individuals colonize a new habitat, genetic drift will more than likely occur. The founder population is small and again the alleles present in this small population will not be representative of the original population. Saltation (from Latin, saltus, "leap") is a sudden change from one generation to the next, that is large, or very large, in comparison with the usual variation of an organism. The term is used for occasionally hypothesized, non gradual changes (especially single-step speciation) that are atypical of, or violate, standard concepts involved in neo-Darwinian evolution.
Genetic drift: Changes in the frequencies of alleles in a population that occur by chance, rather than because of natural selection.
Gene flow: movement of genes into or through a population by interbreeding or by migration.
Gene frequency: The frequency in the population of a particular gene relative to other genes at its locus. Expressed as a proportion (between 0 and 1) or percentage (between 0 and 100 percent).
Gene pool: All the genes in a population at a particular time. Geologic time scale: Tabular record of the divisions of earth history. Major divisions are known as ‘eras’, these in turn are divided into ‘periods’, which are further subdivided into ‘epochs’. Era period epoch geographical time scale Imprinting: a special type of learned behavior in which the learning occurs only during a brief, sensitive period early in the animal’s life; it usually cannot be unlearned. It may involve an attachment for another individual regarded as the animal’s mother and may influence its choice of mate later in life.
Hardy-Weinberg principle: In population genetics, the idea that if a population experienced no selection, no mutation, no migration, no genetic drift, and are randomly mating, then the frequency of each allele and the frequencies of genotype in the population would remain the same (constant) from one generation to the next generation.
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