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Hence, they are not very closely related in evolutionary term; rather are like distant relatives. Can the wing of a butterfly and the wing of a bat be considered homologous organs? Wings of a butterfly are composed of chitinous membrane, while wings of a bat are composed of bony skeleton. Hence, these are not homologous organs rather analogous organs. What are fossils? What do they tell us about the process of evolution? The preserved remains of animals or plants or other organisms from the distant past are called fossils.
These fossils tell us about many extinct animals and also give insights into how the evolution could have taken place. Why are human beings who look so different from each other in terms of size, colour and looks said to belong to the same species?
In spite of wide differences in size, colour and looks, human beings can interbreed. Hence, all of them are kept under one species. If complexity of body design is the criterion, then chimpanzee is obviously better than bacteria. But if ability of survival in almost all kinds of habitat is a criterion then bacteria are far ahead than any other group of organisms. A Mendelian experiment consisted of breeding tall pea plants bearing violet flowers with short pea plants bearing white flowers.
The progeny all bore violet flowers but almost half of them were short. In evolutionary terms, we have more in common with a A Chinese school-boy. A study found that children with light-coloured eyes are likely to have parents with light-coloured eyes. On this basis, can we say anything about whether the light eye colour trait is dominant or recessive? No, since two copies of traits are inherited from parents, one from the mother and the other from the father.
Unless we know the nature of these two variants of traits we cannot tell which is dominant and which is recessive. Recessive traits appear when both the parents contribute recessive allele. From this statement we can only presume are that both parents are contributing recessive allele. How are the areas of study- evolution and classification interlinked?
When we classify organism we look for similarities among organism which allows us to group them. Based on these principles we can work out the evolutionary relationship to the species. Explain the terms analogous and homologous organs with examples. Analogous organs: Such organs which perform a similar function but are different in structure and origin.
Example- Wings of birds and wings of insects. Homologous organs: Such organs which may have different functions but similar structure and origin. Example- forearm of frog, lizard and bird. Outline a project which aims to find the dominant coat colour in dogs. Explain the importance of fossils in deciding evolutionary relationship.
What evidence do we have for the origin of life from inanimate matter? The evidence was given by Stanley L. Miller and Harold C. Urey in Chapter 3 - Metals and Non-metals.
Chapter 4 - Carbon and Its Compounds. Chapter 5 - Periodic Classification of Elements. Chapter 6 - Life Processes. Chapter 7 - Control and Coordination. Chapter 8 - How do Organisms Reproduce? Chapter 9 - Heredity and Evolution. Chapter 10 - Light Reflection and Refraction. Chapter 11 - Human Eye and Colourful World. Chapter 12 - Electricity. Chapter 13 - Magnetic Effects of Electric Current. Chapter 14 - Sources of Energy.
DNA to their offspring. So an offspring will get two versions of that trait from the two parents. Mendel worked out rules for inheritance of these traits. He observed a number of contrasting characters in garden peas and observed their inheritance. Some important terms 1.
Chromosomes are long thread-like structures present in the nucleus of a cell which contain hereditary information of the cell in the form of genes. Contrasting characters: A pair of visible charactes such as tall and dwarf, white and violet flowers, round and wrinkled seeds, green and yellow seeds etc. Dominant trait: The character which expresses itself in a Ft generation is dominant trait.
Example : Tallness is a dominant character in pea plant. Recessive trait: The character which does not express itself but is present in a generation is recessive trait.
Homozygous: A condition in which both the genes of same type are present for example; an organism has both the genes for tallness it is expressed as TT and genes for dwarfness are written as tt. Heterozygous: A condition in which both the genes are of different types Ncert Solutions Class 10th Heredity And Evolution Ii for example; an organism has genes Tt it means it has a gene for tallness and the other for dwarfness only tall character is expressed.
Genotype: It is genetic make up of an individual for example; A pure tall plant is expressed as TT and hybrid tall as Tt. Phenotype: It is external appearance of the organism for example; a plant having Tt composition will appear tall although it has gene for dwarfness. Homologous pair of characters are those in which one member is contributed by the father and the other member by the mother and both have genes for the same character at the same position.
He conducted first monohybrid and then dihybrid crosses. Monohybrid Cross: The cross in which Mendel showed inheritance of dominant and recessive characters is monohybrid cross. To observe inheritance of single pair of contrasting characters he took pure tall genotype TT and pure dwarf genotype tt pea plants and cross pollinated them to obtain first generation or first filial generation. In this figuration F1 generation he obtained only tall plants. This meant that only one of the parental traits was seen, not the mixture of the two.
The plants of F generation or progeny are then self pollinated to obtain F2 generation or progeny. Now all plants were not tall. This indicates that in the F, generation both tall and dwarf traits were inherited but tallness expressed it self.
Tallness is a dominant trait and dwarfness is a recessive trait. F2 generation has a genotypic ratio of 1 : 2 : 1 of three types of plants represented by TT, Tt and tt as shown in the cross.
Law of Dominance: When parents having pure contrasting characters are crossed then only one character expresses itself in the Ft generation. Dihybrid Cross: Mendel also carried out experiments to observe inheritance of two pairs of contrasting characters, which is called dihybrid cross.
He cross breed pea plants bearing round green seed with plants bearing wrinkled and yellow seeds. In the Fx generation he obtained all round and yellow seeds it means round and yellow traits of seeds are dominant features while wrinkled and green are recessive.
He self-pollinated the plants of F: generation to obtain F2 generation, he obtained four different types of seeds round yellow, round green, wrinkled yellow and wrinkled green in the ratio of 9 : 3 : 3 : 1. He concluded that traits are independently inherited. How do traits get expressed? Cellular DNA is the information source for making proteins in the cell.
A part of DNA that provides information for one particular protein is called a gene for that protein for example; the height of a plant depends upon the growth hormone which is in turn controlled by the gene.
If the gene is efficient and more growth hormone is secreted the plant will grow tall. If the gene for that particular protein gets altered and less of it is secreted when the plant will remain short. Both the parents contribute equally to the DNA of next generation during sexual reproduction. They actually contribute a copy of the same gene for example; when tall plant is crossed with short plant the gametes will have single gene either for tallness or for shortness.
F1 generation will get one gene for tallness and other for shortness also. How do germ cells i. Each gene set is present, not as a single long thread of DNA, but as separate independent pieces each called a chromosome. Each cell gets two copies of the chromosome, one from each parent. Each germ cell or gamete has one copy of Ncert Solutions For Class 10th Science Heredity And Evolution it because there is reductional division in the sex organs at the time of formation of gametes. When fertilization takes place normal number of chromosomes is restored in the progeny ensuring the stability of DNA of the species.
How is the sex of a newborn individual determined? It is the process by which sex of a newborn can be determined. Sex determination in human beings: In human beings, all chromosomes are not paired.
Females have a perfect pair both represented by XX. On the other hand males have a normal sized X but the other is short called Y so it is shown as XY. All gametes or ova formed by the homogenetic female are similar i. Males heterogenetic form two types of sperms i.
Sex of the baby will depend on fertilization. There are two possibilities :. Sex chromosomes: Those chromosomes which play a role in determining sex of the newborn.
Evolution: Acquired and inherited traits, Speciation, Evolution and classification, Evolution by stages, Human evolution. Evolution: It is the sequence, of gradual, irreversible changes which took place in the primitive organisms over millions of years to form new present-day species.
Variations that resulted in formation of new species occurred basically due to errors in DNA copying as well as due to sexual reproduction. An Illustration to show variations in a population: A group of twelve red beetles live in green bushes and reproduce sexually so are likely to develop variations.
There are the following possibilities. First situation: Crows eat these beetles as 10th Ncert Heredity And Evolution With they can easily pick up red ones in the green bushes There is a colour variation during sexual reproduction and green beetles appears, it reproduces and its population increases. Crows are not able to see green beetles so their population continues to increase but that of red beetles decreases.
This type of variation gives a survival advantage. Second situation: Due to a colour variation few blue beetle appear forming blue population. Crows can see both red and blue and eat them. Initially there are more of red beetles and less of blue. There is sudden calamity, an elephant kills red beetles by stamping on bush, blue beetles survive reproduce and increase in number.
In this case there is no survival advantage but provides diversity without any adaptation. Third situation: As the population of beetles increases, the bushes suffer from a disease and the availability of food for beetles decreases.
The size of beetles decrease but after a few years as the plant disease is eliminated and enough food is available for the beetles they come back to their normal size. This type of change is not inherited. Acquired Traits: Acquired traits are those which are not inherited over generations as they are caused due to change in the non-reproductive tissue and are not passed on the DNA of the germ cells for example; the size of the beetles in the population decreased due to scarcity of food.
Inherited Trait: Inherited traits are caused due to changes in the DNA of germ cells which are inherited from generation to generation, for example; formation of green beetles in the population of red beetles.
Speciation: It means the development of one or more species from an existing species The factors that could lead to rise of a new species are :. Gene flow: It means the exchange of genetic material by interbreeding between populations of the same species or between individuals within a population. It increases the variation in the genetic composition of a population.
Genetic drift: It is random change in the frequency of alleles in a populate over successive generation due to errors in the gametes. The process is rapid in smaller population. Genetic drift can lead to accumulation of changes in the generations. Natural selection: According to Darwin, natural selection also plays an important role in bringing about evolution of new species of plants and animals.
According to him variations existed between the individuals of a population and some natural phenomena eliminated those individuals which were less adapted.
The surviving population would pass the hereditary advantageous features to their offsprings. With time this process would give rise to organisms different from the original population and new species are formed. Isolation: When a population of a species splits into two, it cannot reproduce with each other and forms a new species, for example; when a population of beetles feed on bushes on a mountain range, some may start feeding on nearby bushes finding entry into a new subpopulation.
They reproduce with them so genes enter in a new population. Ultimately the two groups will be incapable of reproducing with each other and new species will be formed. Evolution and Classification: The organisms show certain features, like appearance and behaviour which are called characteristics for example; Plants can perform photosynthesis. The basic characteristics are shared by a large number of organisms. More characteristics which two species have in common more closely are related, if they are more closely related then they have common ancestors explain the example of brother sister and cousins.
Evolutionary relationships can be traced with the help of the following :. Homologous organs: Those organs which have the same basic structural design and developmental origin but perform different functions and appearance, for example; Forelimbs of frog, lizard, bird, bat and human beings. They have same design of bones but they perform different functions. Analogous organs: Those organs which have different basic design and developmental origin but have similar appearance and perform a similar function, for example; wings of bat and bird.
Wings of bat are folds of skin attached between fingers. But wing of birds are modified forelimbs. Study of Fossils: Fossils are preserved remains of living organisms that lived in the past. When living organisms die their bodies decompose but some parts of their body may be in such an environment that they do not decompose for example; if a dead insect gets caught in hot mud it will not decompose quickly but the mud will harden and retain impressions of the body parts of the insects.
These impressions are also called fossils: The age of fossil can be estimated in two ways : The fossils that occur closer to earth surface are more recent to those found in deeper layers. The second method is isotope dating i. Significance of fossils: Fossils are formed layer by layer in the earths crust. The animals and plants which existed earlier are buried in the deeper layer which ones found in the upper layer. It is found that, deeper fossils have simpler structure than found than upper layer.
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