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CBSE Class 10 Science, Revision Notes, CHAPTER – 09, HEREDITY & EVOLUTION, , Genetics : Branch of science that deals with Heredity and variation., Heredity : It means the transmission of features/ characters/ traits from one, generation to the next generation., Variation : The differences among the individuals of a species/population are called, variations.It takes place due to environment changes,crossing over,and, recombination of genes and mutation., Genotype: The complete set of genes in an organism’s genome is called genotype., Phenotype: The observable characters in an organism make the phenotype., Phenotype is a modified genotype and many of the phenotypes cannot be inherited., Clones are those organisms which are exact copies of each other., Mendel and His Work on Inheritance, Gregor Johann Mendel (1822& 1884) : Started his experiments on plant breeding and, hybridisation. He proposed the laws of inheritance in living organisms., Law of Dominance, Law of segregation, Law of Independent Assortment., Mendel was known as Father of Genetics, Plant selected by Mendel : Pisumsativum (garden pea). Mendel used a number of, contrasting characters for garden pea., , Material downloaded from myCBSEguide.com., , 1 / 16

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Mendel's Experiments : Mendel conducted a series of experiments inwhich he, crossed the pollinated plants to study one character (at a time), Cross between two pea plants with one pair of contrasting characters is called a, monohybridcross., Cross between a tall and a draft plant (short)., , Material downloaded from myCBSEguide.com., , 2 / 16

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Phenotypic ratio : 3:1, Genotypic ratio : 1:2:1, Phenotype ® Physical appearance [Tall or Short], Genotype ® Physical appearance [Tall or short], Observations of Monohybrid Cross, 1. All F1 progeny were tall (no medium height plant (half way characteristic), 2. F2 progeny ¼ were short, 3/4 were tall, 3. Phenotypic ratio F2 – 3 : 1 (3 tall : 1 short), , Genotypic ratio F2 – 1:2:1, Conclusions, 1. TT and Tt both are tall plants while tt is a short plant., 2. A single copy of T is enough to make the plant tall, while both copies have to be ‘t’ for the, plant to be short., 3. Characters/Traits like 'T' are called dominant trait (because it express itself) and ‘t’ are, recessive trait (because it remains suppressed), From these observation, Mendel put forward the rules of inheritance, Law of Segregation: Every individual possesses a pair of alleles for a particular trait. During, gamete formation, a gamete receives only one trait from the alleles. A particular trait can be, dominant or recessive in a particular generation., Dihybrid Cross : A cross between two plants having two pairs of contrasting characters is, called dihybrid cross., , Material downloaded from myCBSEguide.com., , 4 / 16

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Phenotypic Ratio, Round, yellow : 9, Round, green : 3, Wrinkled, yellow : 3, Wrinkled, green : 1, Observations, 1. When RRyy was crossed with rrYY in F1 generation all were Rr Yy round and yellow, seeds., 2. Self pollination of F plants gave parental phenotype and two mixtures(recombinants, round yellow & wrinkled green) seeds plants in the ratio of 9:3:3:1, Conclusions, 1. Round and yellow seeds are DOMINANT characters, 2. Occurrence of new phenotypic combinations show that genes for round and yellow seeds, are inherited independently of each other., Law of Independent Assortment: Alleles of different characters separate independent from, each other during gamete formation., Material downloaded from myCBSEguide.com., , 5 / 16

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In the above example,alleles of texture were assorted independently from those of seed, colour., SEX DETERMINATION, Determination of sex of an offspring., FACTORS, , Sex Chromosomes :In human beings there are 23 pairs of chromosome. Out of these 22, chromosomes pairs are called autosomes and the last pair of chromosome that help in, deciding gender of that individual is called sex chromosome., XX – female, XY – male, , Material downloaded from myCBSEguide.com., , 6 / 16

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This shows that half the children will be boys and half will be girls. All children will inherit, an X chromosome from their mother regardless whether they are boys or girls. Thus sex of, children will be determined by what they inherit from their father, and not from their, mother., EVOLUTION, Evolution is the sequence of gradual changes which takes place in the primitive organisms,, over millions of years, in which new species are produced., Situation - I, , Situation 1 : Green beetles got the survival advantage or they were naturally selected as they, were not visible in green bushes. This natural selection is exerted by crows resulting in, adaptations in the beetles to fit better in their environment, Situation-II, , Material downloaded from myCBSEguide.com., , 7 / 16

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Situation 2 : Blue beetles did not get survivals advantage. Elephant suddenly caused major, havoc in beetle population otherwise their number would have been considerably large., From this we can conclude that accidents can change the frequency of some genes even if, they do not get survival advantage: This is called genetic drift and it leads to variation., SITUATION-III, Group of red beetles, , Habitat of beetles (bushes), Suffer from plant disease, , Average weight of beetles, decreases due to poor nourishment, , Number of beetles kept on reducing, , Material downloaded from myCBSEguide.com., , 8 / 16

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Later plant disease gets eliminated, , Number and average weight of the beetles, increases again, Situation 3 : No genetic change has occurred in the population of beetle.The population gets, affected for a short duration only due to environmentalchanges., ACQUIRED AND INHERITED TRAITS, Acquired Traits, , Inherited Traits, , 1.These are the traits which are developed, , 1. These are the traits which are passed from, , in an individual due to special conditions, , one generation to the next., , They cannot be transferred to the progeny, , 2. They get transferred to the progeny., , They cannot direct evolutioneg. Low weight, , 3. They are helpful in evolution.eg. Colour of, , of starving beetles, , eyes and hair, , SPECIATION, Micro Evolution : It is the evolution which is on a small scale. e.g.change in body colour of, beetles., The process by which new species develop from the existing species is known as speciation., Speciation : it is the process of formation of new species., Species : A group of similar individuals within a population that can interbreed and produce, fertile offspring., Factors which lead to speciation : Geographical isolation,genetic drifts and variations., Geneflow : It is exchange of genetic material by interbreeding betweenpopulations of same, species or individuals, Material downloaded from myCBSEguide.com., , 9 / 16

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WAYS BY WHICH SPECIATION TAKES PLACE, Speciation takes place when variation is combined with geographical isolation., Gene flow :occurs between population that are partly but not completely separated., , GENETIC DRIFT, It is the random change in the frequency of alleles (gene pair) in a population over successive, generations., *Natural Selection : The process by which nature selects and consolidate those organisms, which are more suitably adapted and possesses favorable variations, , Results in Accumulation of different variations in, Sub population, , and, , Genetic drift, Material downloaded from myCBSEguide.com., , 10 / 16

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Genetic drift takes place due to :, (a) Severe changes in the DNA, (b) Change in number of chromosomes, Evolution and Classification, EVOLUTION : the process by which different kinds of living organism are believed to have, developed from earlier forms during the history of the earth, Both evolution and classification are interlinked., 1. Classification of species is reflection of their evolutionary relationship., 2. The more characteristic two species have in common the more closely they are related., 3. The more closely they are related, the more recently they have a common ancestor., 4. Similarities among organisms allow us to group them together and to study their, characteristic., , Material downloaded from myCBSEguide.com., , 11 / 16

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TRACING EVOLUTIONARY RELA TIONSHIPS : Jean Baptiste Lamarck gave the first, theory of evolution. The accepted one is The Origin of Species by Charles Darwin., (Evidences of Evolution), I. Homologous Organs : (Morphological and anatomical evidences. These are the organs that, have same basic structural plan and origin but different functions., Homologous organs provides evidence for evolution by telling us that they are derived from, the same ancestor., Example :, Forelimb of Horse, , (Running), , Winds of bat, , (flying), , Paw of a cat, , (walk/scratch/attack), , Same basic structural plan,, but different functions, perform., , II. Analogous Organs : These are the organs that have different origin and structural plan, but same function example :, Example : Analogous organs provide mechanism for evolution., , Wings of bat, , Elongated fingers with skin, folds, , Different basic structure, but, perform similar function i.e.,, , Material downloaded from myCBSEguide.com., , 12 / 16

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Feathery covering along the, , Wings of bird, , flight., , arm, III. Fossils : (Paleontological evidences), The remains and relics of dead organisms of the past., FOSSILS ARE PRESERVED TRACES OF LIVING ORGANISMS, Fossil Archaeopteryx possess features of reptiles as well as birds. This suggests that birds, have evolved from reptiles., Examples of Fossils, AMMONITE - Fossil-invertebrate, TRILOBITE - Fossil-invertebrate, KNIGHTIA - Fossil-fish, RAJASAURUS - Fossil dinosaur skull, AGE OF THE FOSSILS, , Evolution by Stages, Evolution takes place in stages ie bit by bit over generations., I. Fitness Advantage, Evolution of Eyes : Evolution of complex organs is not sudden it occursdue to minor changes, in DNA, however takes place bit by bit over generations., , Material downloaded from myCBSEguide.com., , 13 / 16

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Insects have compound eyes, Humans have binocular eyes, II. Functional Advantage, Evolutions of Feathers, Feathers {/tex} \to {/tex} provide insulation in cold weather but later they mightbecome, useful for flight., Example : Dinosaurs had feathers, but could not fly using feathers. Birds seem to have later, adapted the feathers to flight., , Evolution by Artificial Selection : Humans have been a powerful agent in modifying wild, species to suit their own requirement through out ages by using artificial selection. e.g. (i), From wild cabbage many varieties like broccoli, cauliflower, red cabbage, kale, cabbage and, kohlrabi were obtained by artificial selection. (ii) Wheat (many varieties obtained due to, artificial selection)., , Material downloaded from myCBSEguide.com., , 14 / 16

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Molecular Phylogeny, It is based on the idea that changes in DNA during reproduction are the basic events, in evolution, Organisms which are more distantly related will accumulate greater differences in, their DNA, Tools to Study Human Evolutionary Relationship, Excavating, Time dating, Fossils, Determining, DNA Sequences, Although there is great diversity of human forms all over the world getall humansare, asinglespecies, GENETIC FOOTPRINTS OF HUMANS, Hundreds/thousand of years ago, , They did not go in a single line, They went forward and backward, Moved in and out of Africa, , Material downloaded from myCBSEguide.com., , 15 / 16

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Sometimes came back to mix with each other., What you have learnt, Variations arising during the process of reproduction can be inherited., These variations may lead to increased survival of the individuals., Sexually reproducing individuals have two copies of genes for the same trait. If the, copies are not identical, the trait that gets expressed is called the dominant trait and, the other is called the recessive trait., Traits in one individual may be inherited separately, giving rise to new combinations, of traits in the offspring of sexual reproduction., Sex is determined by different factors in various species. In human beings, the sex of, the child depends on whether the paternal chromosome is X (for girls) or Y (for boys)., Variations in the species may confer survival advantages or merely contribute to the, genetic drift., Changes in the non-reproductive tissues caused by environmental factors are not, inheritable., Speciation may take place when variation is combined with geographical isolation., Evolutionary relationships are traced in the classification of organisms., Tracing common ancestors back in time leads us to the idea that at some point of time,, non-living material must have given rise to life., Evolution can be worked out by the study of not just living species, but also fossils., Complex organs may have evolved because of the survival advantage of even the, intermediate stages., Organs or features may be adapted to new functions during the course of evolution., For example, feathers are thought to have been initially evolved for warmth and later, adapted for flight., Evolution cannot be said to ‘progress’ from ‘lower’ forms to ‘higher’ forms. Rather,, evolution seems to have given rise to more complex body designs even while the, simpler body designs continue to flourish., Study of the evolution of human beings indicates that all of us belong to a single, species that evolved in Africa and spread across the world in stages., , Material downloaded from myCBSEguide.com., , 16 / 16