Heredity and Evolution

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Heredity and Evolution Genetics is the study of heredity and variation.

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Variation in characters is minimal in asexual reproduction whereas variations accumulate in sexual reproduction. Selection of variants by environmental factors forms the basis for evolutionary process. Transmission of traits from parents to offspring is termed as Heredity. Rules for the inheritance of traits- Mendel’s contributions FATHER OF GENETICS : Gregor Johann Mendel (1822-1884) Both father and the mother contribute practically equal amounts of genetic material to the child. Thus, for each trait there will be two versions in each child. If the two factors are identical, the individual is called homozygous for the trait. If the two factors have different information, the individual is called heterozygous. The alternative forms of a factor are called alleles. Plant on which Mendel experimented-garden pea (common name), Pisum sativum ( scientific name). Law of Segregation (The "First Law") Mendel's Law of Segregation states that allele pairs separate during gamete formation, and randomly unite at fertilization.

Law of Independent Assortment (The "Second Law") Mendel's law of independent assortment states that allele pairs separate independently during the formation of gametes

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Law of dominance  “In a cross of parents that are pure for contrasting traits, only one form of the trait will appear in the next generation. Offspring that are hybrid for a trait will have only the dominant trait in the phenotype.”

 Monohybrid cross

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Dihybrid cross

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Genotipic ratio ; 9:3:3:1 How do these Traits get expressed? Chromosome –DNA- Genes- enzymes- Proteins- Hormones- Plant Height Sex determination

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Evolution Inbuilt tendency to variation during reproduction is due to –  Errors in DNA copying  As a result of sexual reproduction An illustration  Consider a group of twelve red beetles.  They live, let us assume, in some bushes with green leaves.  Their population will grow by sexual reproduction, and therefore, can generate variations.

I situation-

i) Survival advantage ii) Natural selection

II situation-

i) No survival advantage ii) Accidental survival iii) Genetic drift

III situationi) the average weight of adult beetles decreases due to reduced leaf material ii) No genetic change Conclusion  What started out as rare variation came to be a common characteristic in the population  The frequency of an inherited trait changed over generation

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Acquired traits Traits which cannot be inherited over generations There is no change in DNA. These are only life time experiences. Example- reduction in average weight of beetles. Rat tail experiment

Inherited traits Traits which can be inherited over generations There is change in DNA Examples-change in the colour of beetles

Charles Robert Darwin (1809–1882) came up with the idea of evolution of species by natural selection.  Darwin’s theory of Evolution tells us how life evolved from simple to more complex forms and  Mendel’s experiments give us the mechanism for the Inheritance of traits from one generation to the next.  J.B.S. Haldane, a British scientist (who became a citizen of India later), suggested in 1929 that life must have developed from the simple inorganic molecules which were present on earth soon after it was formed.  The experiment conducted by Stanley L. Miller and Harold C. Urey in 1953 proved Haldane‟s theory. They assembled an atmosphere similar to that thought to exist on early earth (this had molecules like ammonia, methane and hydrogen sulphide, but no oxygen) over water. This was maintained at a temperature just below 100°C and sparks were passed through the mixture of gases to simulate lightning. At the end of a week, 15% of the carbon (from methane) had been converted to simple compounds of carbon including amino acids which make up protein molecules.

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Speciation  Micro Evolution- the changes are small, even though significant.  Origin of new species from the existing one is called speciation.

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Evolution and classification  A characteristic is a particular form or a particular function.

 The more characteristics two species will have in common, the more closely they are related.  And the more closely they are related, the more recently they will have had a common ancestor

Grandparent

Parent

Brother

Parent

Sister

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Cousins

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Tracing Evolutionary Relationships Homologous and analogous organs Vestigial organs Fossils Body design Artificial selection Molecular Phylogeny

 Homologous and analogous organs  Homologous organs - Organs which have different functions but similar structure and origin. Example ;fore arm of frog , lizard ,bird and human

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 Analogous organs-Organs which perform similar function but are different in structure and function. Example - the wings of a bat and the wings of a bird.

 Vestigial organs Organs which are appear functionless in one organism and functional in some other.

 Fossils 10

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Fossils are the petrified remains or impressions of the ancient animals and plants preserved in rocks.

 Body design  The structure of the eye in different organisms is different.  A change that is useful for one property to start with can become useful later for quite a different function. For example; feathers- provided insulation from cold later used for flight.  Artificial selection 11

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 Artificial selection is the process by which man selects traits useful to him for improving the qualities.  Example of wild cabbage; very dissimilar looking structures evolved from common ancestral design.

 Molecular Phylogeny  Trace the changes in DNA backwards in time and find out where each change diverged from the other.  This approach is based on the idea that organisms which are more distantly related will accumulate a greater number of differences in their DNA. EVOLUTION SHOULD NOT BE EQUATED WITH ‘PROGRESS’  Evolution is simply the generation of diversity and the shaping of the diversity by environmental selection. 12

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 The only progressive trend in evolution seems to be that more and more complex body designs have emerged over time.  Still so many of the older and simpler designs still survive.  Evolution is like a tree not like a ladder

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Human Evolution Tools for tracing evolutionary relationships – excavating, time-dating studying fossils, and determining DNA sequences People used to talk about human „races‟. Skin colour used to be the Commonest way of identifying these so called races. All humans are a single species.

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The earliest members of the human species, Homo sapiens, can be traced from Africa.

 MASTER CARD Organic evolution is a process by which new species develop from earlier forms. Transmission of traits from parents to the offspring is called heredity. Natural selection and variation are the basic events in evolution. The gradual unfolding of organisms from pre-existing organisms through change since the origin of life is termed evolution. Archaeopteryx – link between birds and reptile. Theory of natural selection given by Charles Darwin. Theory of inheritance of acquired characters given by Lamarck. The elimination of the genes of certain traits when a section of a species population migrates or dies of natural calamity is genetic drift. Genes are the unit of inheritance. Origin of species – book by Darwin. F1-first filial generation F2- second filial generation Mendel used the word FACTORS for genes.

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