CBSE Class 10 Science Heredity And Evolution Notes Set 03

Heredity and Evolution

Genetics : Branch of science that deals with Heredity and variation.

Heredity : It means the transmission of features/ characters/ traits from one generation to the next generation.

Variation : The differences among the individuals of a species/ population are called variations.

MENDEL AND HIS WORK ON INHERITANCE

Gregor Johann Mendel (1822&1884) : Started his experiments on plant breeding and hybridisation

Mendel ® was known as Father of Genetics Plant selected by Mendel : Pisum sativum (garden pea). Mendel used a number of contrasting characters for garden pea.

Mendels Experiments : Mendel conducted a series of experiments in which he crossed the pollinated plants to study one character (at a time)
Monohybrid Cross :
Cross between two pea plants with one pair (monohybrid cross) contrasting characters
Example : Tall / Short Plants.

Evolution
SITUATION-I

Situation 1 : Green beetles got the survival advantage or they were naturally selected as they were not visible in green bushes. This natural selection is exerted by crows resulting in adaptations in the beetles to fit better in their environment

SITUATION-II

Situation 2 : Blue beetles did not get survivals advantage. Elephant suddenly caused major havoc in beetle population otherwise there number would have been considerably large.

From this we can conclude that accidents can change the frequency of some genes even if they do not get survival advantage: This is called genetic drift and it leads to variation.

Mechanism of Heredity 
Characters or traits of an organism are controlled by the genes

Genetic drift. It leads to diversity without any adaptation 

SITUATION-III

Situation 3 : No genetic change has occured in the population of beetle. The population gets affected for a short duration only due to environmental changes 

Acquired and Inherited Traits

Speciation

Micro evolution : It is the evolution which is on a small scale. eg. change in body colour of beetles.
Speciation : it is the process of formation of new species.
Species : A group of similar individuals that along to a population that can interbreed and produce ferrite off spring.
Geneflow : It is exchange of genetic material by interbreeding between populations of same species or individuals

Genetic Drift

It is the random change in the frequency of alleles (gene pair) in a population over successive generations.
*Natural Selection : The process by which nature selects and consolidate those organisms which are more suitably adapted and posesses favorable variations 

Genetic drift takes place due to
a) Severe changes in the DNA
b) Change in number of chromosomes
Evolution and classification
Both evolution and classification are interlinked.
1. Classification of species is reflectionof their evolutionary relationship.
2. The more characteristic two species have in common the more closely they are related.
3. The more closely they are related, the more recently they have a common ancestor.
4. Similarities among organisms allow us to group them together and to study their characteristic 

Tracing Evolutionary Relationships
(Evidences of Evolution)

I. Homologous Organs : (Morphological and anatomical evidences. These are the organs that have same basic structural plan and origin but different functions. 

III. Fossils : (Palaeontological evidences)
The remains and relics of dead organisms of the past.

Example :
i) Fossil of wooly mammoth
ii) Archeopteryx (fossil bird)
iii) Dead insect caught in hot mud.
FOSSILS ARE PRESERVED TRACES OF LIVING ORGANISMS
Eg. AMMONITE - Fossil invertebrate
TRILOBITE       - Fossil in vertebrate
KNIGHTIA        - Fossil fish
RAJASAURUS   - Fossil dinosaur skull

AGE OF THE FOSSILS  

II. Functional Advantage
♦ Evolutions of feathers
Feathers  provide insulation in cold weather
but later they might become useful for flight.
Example :
Dinosaurs had feathers, but could not fly using feathers. Birds seem to have later adapted the feathers to flight.

Artificial Selection :
Humans have been a powerful agent in modifying wild species to suit their own requirement through out ages by using artificial selection. eg (i) Wild cabbage the dissimilar looking structures have evolved from a common ancestral design. (ii) Wheat (many varieties obtained due to artificial selection) 

Molecular Phylogeny :
♦ It is based on the idea that changes in DNA during reproduction are the basic events in evolution
♦ Organisms which are more distantly related will accumulate greater differences in their DNA 

Human Evolution 

♦ They did'nt go in a single line
♦ They went forward and backward
♦ Moved in and out of Africa
♦ Sometimes came back to mix with each other.

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