Science Class 10 Notes for Heredity and Evolution
1. The transmission of characters from parent to their off springs is known
as heredity.
· The study of heredity and variations is known as
genetics.
· Clones are those organisms which are the carbon copies of
one another.
· Variation in sexually reproducing organisms are caused
due to the following factors like
environment, crossing over and
recombination of genes and mutation.
· The first study of inheritance was done by Gregor Mendel
on garden pea.
· Paired condition of chromosomes is known as diploid.
· Unpaired condition of chromosomes is known as haploid.
· DNA (Deoxyribo Nucleic Acid), RNA (Ribo Nucleic Acid) is
the genetic material in
all organisms.
2. Mendel’s laws of inheritance are
(i) Law of Dominance
(ii) Law of Segregation (Law of purjty of gametes)
(iii) Law of Independent Assortment
3. Genotype is the composition of genes present in an organism and the
characteristic which
is visible in an organism is called its phenotype.
4. When two parents cross (or breed) to produce progeny (or offsprings),
then their progeny
is called F1-generation (First Filial Generation) and when the first
generation progeny
cross among themselves to produce second progeny, then this progeny is
called F2-generation
or second Filial Generation.
· Mendel conducted his famous experiments on garden pea
(Pisum sativum).
· He used a number of contrasting characters like round /
wrinkled seeds, tall/ short
plants, white/ violet flowers and so
on.
5. During Monohybrid Cross
· When tall pea plants are crossed with short pea plants
then in Fi generation only tall
plants were obtained.
· 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.
· In dihybrid cross two pairs of contrasting characters
were considered. Tall plant with
round seeds were crossed with short
plant with wrinkled seeds. In Fi tall plants with
round seeds were obtained. On selfing
these F, plants with F2 produced tall plants with
round seeds, short plant with
wrinkled seeds and some new combinations (tall plant
with wrinkled seeds and short plant
with rounds seeds) were also obtained. The
tall/short trait and round wrinkled
traits are independently inherited.
· The expression of a particular trait is controlled by
gene.
6. DNA is the source of making protein in a cell.
The section of DNA that provides information for one protein is called
gene.
7. Physical and Chemical Basis of Heredity
Mendel (1866) said that heredity was controlled by particles, called
germinal units, or factors.
8 Sex determination is the process by which the sex of a person is
determined.
All human chromosomes are not paired. 22 pairs are called autosomes. Women
have a perfect
pair of sex chromosomes XX. But men have a mismatched pair XY.
9. 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.
A. The evidences of evolution are :
i. Homologous organs,
ii. Analogous organs, and
Fossils
B. Theories of Evolution
Jean Baptiste Lamarck gave the first theory of evolution.
Darwin’s Theory of
Evolution
Charles Robert Darwin (1809-1882) explained the evolutionary principle in
his famous book
“The origin of species”. The theory proposed by him is popularly known as
theory of natural
selection or Darwinsim.
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
10. Speciation : The
process by which new species develop from the existing species is known
as speciation.
The factors which leads to speciation are :
· Geographical isolation
· Genetic drift and
· Variations
11. Classification
Evolutions are of three types :-
(i) Convergent Evolution
(ii) Divergent Evolution, and
(iii) Parallel Evolution.
12. Fossils : The
remains of dead plants or animals that lived in the remote past are known as
fossils.
Various kinds of fossils are : Ammonite, Trilobite and Dinosaur.
13. Evolution by Stages : Evolution of complex organs have taken place bit-by-bit
over generations.
For example eye, feathers of birds have evolved because of survival
advantage of intermediate
stages.
Thus changes in DNA during reproduction are the main cause of evolution.
14. Human Evolution : All have beings belong to single speceis Homo sapiens, although
there were many races of humans.
They have originated in Africa, some ancestors left Africa and migrated to
West Asia,
Central Asia, Eurasia South Asia, East Asia, Indonesia, Australia, America,
while others stayed
there.
Excavating, time-dating, studying fossils, determining DNA Sequences have
been used for
studying human
evolution.