These comprehensive RBSE Class 10 Science Notes Chapter 9 Heredity and Evolution will give a brief overview of all the concepts.
RBSE Class 10 Science Chapter 9 Notes Heredity and Evolution
→ The reproductive processes give rise to new individuals that are similar, but subtly different.
→ During reproduction, the variations arises can be hereditary. These variations increases the chances of survival of the organisms.
→ Offsprings developed by asexual reproduction are very much similar but comparatively more variations are found in sexual reproduction.
→ Variations in a species have not equal chances of surviving. Depending on the nature of variations, different individuals would have different kinds of advantages. Bacteria that can withstand heat will survive better in a heat wave.
→ Heredity-From parent organism the transfer of trait and characters in offspring is called heredity. The rule of heredity determines the process by which traits and characteristics are reliably inherited.
→ Inherited traits-A child bears all the basic features of a human being. However, it does not look exactly like its parents, and human populations show a great deal of variation.
→ The laws of inheritance of traits in humans are based on the fact that both the mother and father transfer the same amount of genetic material to the offspring (infants).
→ Gregor Johann Mendel (1822-1884) did experiment and gave the laws of inheritance, due to this Mendel is called the father of genetics.
→ Mendel used a number of contrasting visible characters of garden peas-round/ wrinkled seeds, tall/short plants, white/violet flowers and so on.
→ Definition of related terms of Mendel’s experiment –
(i) Factor – When Mendel did the experiment, upto that time chromosome and gene was not discovered. So Mendel called this structure as the factor in place of gene which controls these characters.
(ii) Hybridization – The process of crossing or fertilisation between organisms of two species and to obtain the new offspring is called hybridization.
(iii) Hybrid – Offspring produced by crossing between the organisms of two species is called hybrid.
(iv) First Filial – First generation produced by cross of two parents is called first filial or F1.
(v) Sexually reproducing individuals have two copies of genes for the same trait. If the copies are not identical the trait that get expressed is called the dominant trait and the other is called the recessive trait.
(vi) Genotype – The genetic composition (i.e., gene structure) is the genotype.
(vii) Phenotype – The external character of organism is called phenotype, like tall, dwarf, red, green colour.
(viii) Allelomorphic – The gene which controls or expresses one character in an organism, is present, in two alternate forms is called alleles.
(ix) Homozygous – If both genes of the organism are similar types like TT or tt then it is homozygous. If both genes are different types like Tt, then organism is heterozygous.
(x) Back Cross – When in hybridization offspring of F1 i.e., hybrid individual is crossed with any parent is called back cross.
(xi) Monohybrid Cross – When only one pair of alleles is used during crossing, is called monohybrid cross.
(xii) Dihybrid Cross – When two pairs of alleles is used during crossing, is called dihybrid cross.
(xiii) Pure Variety – Such organism which is particular for a character (trait) produces the same type of character in organism upto many generations, is called pure variety.
(xiv) Test Cross – When F1 generation heterozygous hybrid is crossed with homozygous recessive parent, is called test cross.
→ Law of Unit Character-All characters found in organism are controlled by genes. For every character there is a gene. This gene always remains in pair. In each pair one factor (Mendel called it factor and then it was called gene) comes from mother and second from father.
→ A section of DNA that provides information for one protein is called the gene for that protein.
→ Law of Inheritance-Gregor Johnn Mendel resident of Austria gave three laws of inheritance
(i) Law of Dominance-According to this when crossing is done by keeping consideration of one pair of opposite characters. The character appear in first generation called dominant and other character which is hidden, is recessive.
(ii) Law of Segregation-During sexual reproduction when gametes are formed then only allel participate in gamete formation, therefore gametė are completely pure for that choice. According to this law in F1 hybrid generation plants both opposite characters are present in pair. These characters get separated in F2. Due to this it is called law of segregation.
(iii) Law of Independent Assortment-According to this on crossing the two plants consisting two pairs of opposite characters, these characters segregate or separate independently and inheritance of one character is not effecting the inheritance of other character.
→ Sex Determination-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) and Y (for boys).
→ Acquired Characters-Acquired characters by life processes can not pass on to its progeny. Example, tails of mice are cut upto many generations but these mice will not produce the tailless mice.
→ 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.
→ Theory of Natural Selection – According to Darwin, only those individuals survive which are adapted to environment. Those animals which do not adapt to environment, slowly and slowly are destroyed. In this way nature selects the organism and evolve the new species. Darwin was a naturalist and his research was on the role of earthworm in maintaining the soil fertility.
→ Isolation-In nature the process of inhibiting the free interbreeding between the organisms of two species, is called isolation. In organism there are three types of isolation present-
- Geographical isolation
- Spatial isolation
- Germinal isolation.
→ Speciation-Isolation is important for speciation. It stops the interbreeding and adapts to live in new habitat. By this new characters develop in organism. As a result the natural selection is affected, and helps in formation of new species.
→ Evolution-By process of very slow rate and sequencial changes existing different species of plants and animals evolved from already present species on earth is called evolution.
→ 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 side to life.
→ 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 adopted for flight.
→ Complex organs may have evolved because of the survival advantage of even the intermediate stages.
→ Homologous Organs-The organs which have same basic structure and origin but differ in function, are called homologous organs.
→ Analogous Organs-Organs similar in function but differ in basic structure and origin are called analogous organs.
→ Vestigial Organs-Such organs found in body which were functional in their ancestral state but now they have no apparent function, are called vestigial organs.
Example-Nictitating membrane, ear pinna.
→ Fossils -The remanents of dead organism found in old rocks or impression are called fossils. To determine the age of fossil, there are two approaches (i) relative (ii) dating of fossil.
→ Fossil Dating-For dating purpose radioactive isotopes are used. In this method ratios of different isotopes like 14C etc., are calculated.
→ 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.