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Science Class 10 Notes for Heredity and Evolution
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The study of heredity and variations is known as genetics
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Variation in sexually reproducing organisms are caused due to the following factors like
environment, crossing over and recombination of genes and mutation
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Paired condition of chromosomes is known as diploid
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DNA (Deoxyribo Nucleic Acid), RNA (Ribo Nucleic Acid) is the genetic material in
all organisms
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Mendel’s laws of inheritance are
(i) Law of Dominance
(ii) Law of Segregation (Law of purjty of gametes)
(iii) Law of Independent Assortment
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Mendel conducted his famous experiments on garden pea (Pisum sativum)
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F2 progeny ofFi tall plants are not all tall but one quarter of them are short indicating
that both tallness and shortness traits were inherited in F1 but only tallness trait was
expressed due to dominance
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Tall plant with
round seeds were crossed with short plant with wrinkled seeds
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On selfing these F, plants with F2 produced tall plants with
round seeds, short plant with wrinkled seeds and some new combinations (tall plant

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with wrinkled seeds and short plant with rounds seeds) were also obtained
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The expression of a particular trait is controlled by gene
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DNA is the source of making protein in a cell
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8 Sex determination is the process by which the sex of a person is determined
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22 pairs are called autosomes
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But men have a mismatched pair XY
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Evolution
It is the sequence of gradual changes which take place in the primitive organisms over
millions of years in which new species are produced
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The evidences of evolution are :
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Analogous organs, and
Fossils
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Darwin’s Theory of Evolution
Charles Robert Darwin (1809-1882) explained the evolutionary principle in his famous book
“The origin of species”
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The main features of the theory of natural selection are as follows:
(i) Over production
(ii) Limited food and space
(iii) Struggle for Existence
(iv) Variations
(v) Natural Selection or Survival of the Fittest
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The factors which leads to speciation are :
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Geographical isolation
Genetic drift and
Variations

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Various kinds of fossils are : Ammonite, Trilobite and Dinosaur
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Evolution by Stages : Evolution of complex organs have taken place bit-by-bit
over generations
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Thus changes in DNA during reproduction are the main cause of evolution
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Human Evolution : All have beings belong to single speceis Homo sapiens, although
there were many races of humans
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Excavating, time-dating, studying fossils, determining DNA Sequences have been used for
studying human evolution
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ncerthelp

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