1. HEREDITY AND EVOLUTION
PREPARED BY:JEHANGEER HAMEED
(10th class)

2. ACCUMULATION OF VARIATIONS DURING REPRODUCTION
Variations in organisms mainly occur during sexual reproduction
Because of mutations caused by errors in DNA replication. Thus no two
Offspring's are identical to each other .Other causes of such variations
are crossing over during meiosis separation of chromosomes during gametogenesis from both parents at the time of fertilization.
Hence we see that each generation provides the next
Generation with some variations though the body design remains the same. Some new variations are also produced in the new generation. The variations keep on accumulating and passing to more individuals in each generation. Thus as we proceed to later generation the frequency of variations goes on increasing.

3. HEREDITY
Heridity means continuity of features from one generation to another.Heridity can be defined as “resemblances among individuals related by descent” or “ the transmission of traits from parents to offspring's”.
From biological point of view variation can be defined as “ the occurrence of differences among the individuals”Heridity and variation are important aspects of the branch of biology which is known as GENETICS. That’s why Genetics is called the ‘SCIENCE OF HERIDITY ANDVARIATIONS.’
The concept of heredity is not new. Selective breeding of horses and cattle used to be done during the ancient civilization of Babylon and Assyria. Ancient Chinese writings mention about creating better varieties of paddy. But the scientific principles, which governs patterns of inheritance ,were unknown till the experiments and findings of GREGOR JOHANN MENDEL( ).His observations regarding the occurrence of contrasting characters in various generation of

4. Garden of pea plant led him to interpret that these are controlled by units which he called “FACTOR”. Though Mendel published his conclusions and results much earlier ,they came to be known to the world in the year 1990, many years after his death. He considered each and every character as a unit, which is controlled by a factor Mendles facter , the carriers of heridity information ,are what we known today as “GENES’. A term coinrd by JOHANSSEN in The principle of inheretance explained by Mendel was based on his experiments with garden pea Mendel observed that two tyoes of pea plants were growing in his monastry. He also observed that pea had different pairs of contrasting traits, including height, flower colour, flower position, seed shape, seed colour, pod shape, pod colour.He now begin his work upon them and raised a these varieties by first true breeding and then cross breeding. These offsprings were called F and allowed to self breed. The results of this experiment were published as “EXPERIMENTS ON PLANT HYBRIDIZATION”.

5. The seven contrasting traits selected by Mendel in his experiment the given below: CHARACTER = DOMINANT TRAIT = RECESSIVE TRAIT SEEDSHAPE = ROUND = WRINKLED SEED COLOUR = YELLOW = GREEN FLOWER COLOUR = VIOLET = WHITE POD SHAPE = FULL = CONSTRICTED POD COLOUR = GREEN = YELLOW FLOWER POSITION= AXIAL = TERMINAL STEM HEIGHT = TALL = DWARF

6. MENDELS EXPERIMENTAL TECHNIQUE
Mendel conducted breeding experiments in three steps:
Selection of pure parent plants
Production of first generation of plants by cross breeding
Raising of second and subsequent generations by self fertilization of hybrids.
MENDELS MONOHYBRID CROSS:
A breeding experiment dealing with a single character is called a monohybrid cross
Mental first selected ‘pure line’ plants(i.e., the plants that produced similar traits generation after generation). He, then, cross pollinated such plants having the contrasting traits, considering one trait at a time. For instance, in one such cross breeding experiment, he cross bred garden pea plant having round seeds with plant having wrinkled seeds. In this monohybrid cross, the pollen grains from the flower of the desired plant raised from round seeds were transferred over the previously emasculated flower of a plant raised from wrinkled seeds or vice-versa. After the transfer of pollen grains, the cross pollinated flower was properly covered and seeds produced were allowed to mature. All the seeds F1 generation were carefully observed. Mental observed that all the seeds of F1 generation were of round type and there were no intermediate characteristics.
He raised plants from F1 seeds and allowed the flowers to self- pollinate to produce the seeds of F2 generation. The flowers were kept covered from the beginning to avoid unwanted pollens to reach these flowers. In F2 generation, Mendel observed the appearance of both round and wrinkled seeds in approximately 3:1 proportion.

7. MENDELS DIHYBRID CROSS A breeding experiment dealing with two characters at the same time is called a dihybrid cross In one such cross ,Mendel considered shape as well as colour of the seeds simultaneously. He selected pure line plants and then cross pollinated flowers raised from seeds of round shape and yellow colour with those from wrinkled seeds and green colour. Mendel observed that in F generation all seeds had the features of only one parental type ie.,round shape and yellow color. He raised plants from F generation seeds allowed the flowers to self pollinate to produce the seeds of next generation. These flowers were kept covered from the beginning. In second generation ,Mendel observed the appearance of four types of combinations. These included two parental types (round shaped and yellow coloured seeds, and wrinkled shaped and green coloured seeds) and two new combinations(round shaped and green coloured seeds and wrinkled and yellow coloured seeds) in approximately same proportion.

8. STRUCTURE OF DNA
The expanded form of DNA is deoxyribonucleic acid. It was first isolated by the scientist FREDERICK MEISHER from the nucleus of the puss cells in He named it as NUCLEIN or nucleic acid because of its acidic nature. DNA is the carrier of the genetic information from generation to generation. It transmits the hereditary characters in a coded language from parents to the offspring's.
DNA is a macromolecule or polymer. It is made of very large number of nucleotide units and hence is termed polynucleotide.
Each nucleotide unit in a DNA molecule is made of three components:
(a)Deoxyribose sugar:It is a pentose sugar represented as “S”
(b)Nitrogenous base: Each nucleotide unit has a nitrogen containing base.

9. HOW DO TRAITS GET EXPRESSED
In a DNA molecule, nitrogenous bases are of two types:
(a) PURINES: The purines in a DNA molecule are Adenosine(A) and Guanine(G).
(b) PYRIMIDINES: The pyrimidines in a DNA molecule are Cytosine(C)) and Thymine(T)
3.PHOSPHATE GROUP: The phosphate group contains one phosphorus atom and four specifically linked oxygen atoms.
Thus , there are four types of nucleotides in a DNA molecule depending upon the kind of nitrogenous base present in each nucleotide.
HOW DO TRAITS GET EXPRESSED
According to Mendel's interpretations, both parents are contribute equally to the DNA of the progeny during sexual reproduction.Also,both parents help in determining the traits in the progeny. In other words, both parents contribute a copy each of the same genes and both male and female gamets,therefore have only one set of genes.

10. THEORIES ON ORIGIN OF LIFE;
1.Theory of special creation: It stated that life was created by the wishes of a divine being or some supernatural power, THE CREATOR OR GOD out of nothing at a particular time in the remote past. According to CHRISTIAN belief, God created the universe,plants,animals and human beings in six natural days. Adam and Eve were the first man and woman created by God. According to Hindu mythology, Lord Brahma creates the world with his wish.
The theory of special creation is purely a religious concept. It is not based on scientific principles.
2.THEORY OF SPONTANEOUS GENERATION: It stated that life originated spontaneously from non- living materials- abiogenesis.For example, fly larvae were believed to develop from rotten meat; frogs, snakes and crocodiles could form from the moist soil of the river. However , this idea was laid to rest by LOUIS PASTEUR who experimentally proved that microorganisms, such as protists and bacteria, arise from the pre-existing micro organisms of their kind.

11. ABIOGENIC OR NATUALISTIC THEORY OR CHEMICAL ORIGIN OF LIFE;
It is now well accepted that life originated from inanimate matter by a series of chemical reactions on the primitive earth. This concept was put forward by ALEXANDER.I.OPARIN J.B.S.HALDANE INDEPENDENTLY. This theory is now known as primary a biogenesis.
J.B.S.HALDANE,a British scientist suggested in that life must have arisen on the primitive earth from collection of chemicals through a progressive series of chemical reactions in which atoms combined into inorganic molecules, inorganic molecules into simple organic compounds, simple organic compounds into the living matter. The primary abiogenesis is thought to have occurred about 3.6 billion years ago. HALDANE speculated that the conditions on the primitive earth were far from the conditions we see today. The atmosphere was highly reducing and oxygen in molecular form was not available.

12. EVOLUTION
The term evolution has been derived from the Latin word “evolvere” which means to “unroll” or unfold. It refers to a gradual change from one form to another. Such a change in elements with time is called inorganic evolution. However gradual change in living organisms with time since beginning of life is termed organic evolution’
The concept of organic evolution was first given by CHARLES DARWIN which simply means “DESCENT WITH MODIFICATION". This doctrine of organic evolution states that the present day complex organisms have originated from the earlier simpler forms of life during the course of ages by the process of gradual change.
So, evolution is the constant process of gradual change occurring in the organisms since the origin of life that has given rise to enormous variety of complex organisms on this earth.

13. SPECIATION
Origin of new species from the existing one is called speciation.
(REFER TEXT BOOK)
REPRODUCTIVE ISOLATION:
Reproductive isolation refers to the m mechanisms which check the populations of two different groups from interbreeding.
Reproductive isolation may happen in no. of ways:
(a) TEMPORAL ISOLATION: It is the failure of two groups to interbreed because they breed at different times(seasons) of the year.
(b)BEHVIOURAL ISOLATION: It prevents interbreeding of two groups due to differences in courtship and mating behavior.
©PHYSIOLOGICAL ISOLATION: It is the functional incompatibility in mating or in production and survival of gametes.

14. (d)MECHANICAL ISOLATION: It is the difference in size or structure of genitalia between two groups that make interbreeding difficult or impossible.
EVIDENCES OF EVOLUTION:
1.MORPHOLOGICAL AND ANATOMICAL EVIDENCES:
These evidenes are based on the similarities in the external and internal features of the different kinds of organisms. These features are:
(a)HOMOLOGOUS ORGANS: The organs which perform different functions in different species but have similar basic structure and similar embryonic origin are called homologous organs.
For example the forelimbs of a frog, a lizard, a bird and a human being show similarity in basic structure. The forelimbs in all these different vertebrates also develop in similar fashion. However ,these organs perform entirely different functions:theforelimbs of a frog help the animal to prop up the front end of the body at rest and also act as shock absorbers when the animal lands on the ground after a leap; the forelimbs of a lizard are modified for creeping movements; the forelimbs of a bird are modified for flying purposes, while forelimbs of a human being are used for grasping.

15. (b).ANALOGOUS ORGANS
The organs which are quite different in fundamental structure and embryonic origin but performs same function and may superficially look alike in entirely different species are called analogous organs.
The wings of an insect and a bird are analogous organs. It is so because both these organs in entirely different animals perform similar functions,ie,they are used for flying in the air. However, they are very different in structure .An insect wing is a fold of membrane which is supported with few muscles. On the other hand, wings of a bird are formed of limb bones covered with flesh, skin and feathers
(c)VESTIGIAL ORGANS: The organs which occur in reduced form and are useless to the possessor, but are homologous to the fully developed, functional organs in the ancestors or related forms are called vestigial organs. For instance vermiform appendix of the large intestine and nictitating membrane in the eye of human beings are vestigial organs.

16. 2.EMBRYOLOGICAL EVIDENCES:
Embryology refers to the study of development of an embryo of organisms from fertilized egg to young one. Study of embryology of different animal groups shows striking structural similarities between them. The early embryos of all the vertebrates resemble in shape and structure. The resemblance of early embryos offish,salamander,tortoise,chick,rabbit and man is so close that it is very difficult to distinguish them from each other. This similarity among the early embryos shows that all the vertebrates have evolved from a common ancestor. Above observations led EARNST HAECKEL to propose a law which is popularly known as the biogenetic law. This law can be briefly put in three words ontogeny repeats phylogeny or ontogeny recapitulates phylogeny. It simply means that an organisms repeats its ancestral history during its embryonic development.

17. BIOGENETIC LAW PALAEONTOLOGICAL EVIDENCES
The biogenetic law states that an animal in its individual embryonic development from egg to adult repeats or recapitulates in condensed form the stages through which its ancestors have passed in the course of their evolution.
PALAEONTOLOGICAL EVIDENCES
Paleontology is the study of past life based on the fossil record.
Normally, when the organisms die, their bodies are decomposed and lost.However,if the body or some of its parts remain in an environment that does not let it decompose completely, the body or its parts will eventually be preserved leave the impressions. For instance, if a dead insect gets caught in mud, it will not decompose quickly; the mud will eventually harden and retain the impressions of the body parts of the insect.Thus,the fossils are the impressions of the dead animals and plants that lived in the remote past.

18. SOLVED NCERT TEXT BOOK INTEXT QUESTIONS:
1.If a trait exists in 10% of a population of an asexually reproducing species and a trait B exists in 60% of the same population, whish trait is likely to have arisen earlier.
Ans.Trait B
In asexual reproduction, there is no reshuffling of traits.Thus,appearance of few new traits in the population occurs due to mild inaccuracy in DNA copying process.Hence,few new traits occur than the already existing traits.
2.How does creation of various in species ensure survival?
Ans.The process of natural selection selects the species with favorable variations according to the surrounding conditions and prevailing environment. The individuals whose variations are useful, increase in number through differential reproduction and species survival is ensured.

19. 3. A man with blood group A marries a woman with blood group O
3.A man with blood group A marries a woman with blood group O.Their daughter has blood group O.Is this information enough to tell you which of the traits blood group A or O is dominant? why or why not?
Ans.This information is not enough. This is because each individual is carrying two allels.The recessive trait can occur only when two alleles are similar. If blood group A is dominant and O is recessive, then daughter can have blood group O only when both recessive alleles occur together in mother, and father has one allele of O and other of A.
4.Why are traits acquired during the life time of an individual not inherited?
Ans.It is so because acquired characters involve changes in the non-reproductive tissues only and do not bring any change in the DNA. Any alteration in the DNA,in fact, is passed through germ cells to the next generation.

20. 5.Why are small numbers of surviving tigers a cause of worry from the point of view of genetics'? Ans.Tigers are surviving in limited numbers. If some natural calamity kills these small population of tigers, they will suddenly become extinct as per genetic drift phenomenon. 6.Will geographical isolation be a major factor in the speciation of a self pollinating plant species? Why or why not? Ans.Geographical isolation will not be a major factor for the speciation of a self-pollinating plant species because the pollination is occurring on the same plant and a natural barrier can occur between different organisms. 7.What are fossils? What do they tell us about the process of evolution? Ans.Fossils are the remains or impressions of the dead animals and plants that lived in the remote past. They are the direct evidences in support of organic evolution and help in determining evolutionary relationship between organisms.

21. 8.Can the wing of a butterfly and the wing of a bat be considered homologous organs? Why or why not? Ans.No.It is so because the wings of a butterfly and a wing of a bat perform similar functions,ie,they are used for flying in the air.However,they are very different in fundamental structure and embryonic origin. In other words, they are analogous organs. The superficial similarity of these organs is due to adaptation to flying rather than to inheritance from a common ancestor. BEST OF LUCK