1. Heredity & Evolution
Heredity:-
The transfer of biological characters from one generation to next generation via genes is called as heredity
Gregor Johann Mendel is the father of modern genetic
Historical Background:-
1. 1900 – Vries, Carl, Enrich rediscovered Mendelian research
2. 1901 – Hugo De Vries put forth mutational theory
3. 1902 – Walter & Sutton observed the paired chromosomes
4. 1944 – Ostwald Avery, Mclyn MaCarthy & Colin MacLeod proved DNA as a genetic
materialof all living things except viruses.
5. 1953 – Watson & Crick proposed double helical model of DNA
6. 1961 – Francois Jacob & Jack Monad proposed model for protein Synthesis
Transcription, Translation and Translocation
Transcription:-
Synthesis of mRNA as per the nucleotide sequence present on the DNA molecule is called as process of transcription.
Gene:-
The nucleotide sequence present in the DNA molecule is called gene.
They controls the structure and functioning of the cells of the body. Information required for the synthesis of proteins is stored in the genes.
Central dogma:-
Synthesis of proteins by DNA through the RNA is called central dogma.
Triplet codon:-
The code for each amino acid consisting of three nucleotides is c/as triplet codon.
Thousands of triplet codons are present in each mRNA molecule.
Translation:-
As per the codon on mRNA, the tRNA molecule with complementary
anticodon is brought near mRNA is called translation.
The ribosomes keeps on moving from one end of mRNA to other end by
the distance of one triplet codon. This process is called as translocation.
Mutation:
Sometimes sudden changes occur in genes, this is called as mutation.
Some mutations may be minor or some may be taken into consideration.
Example : Mutation may cause genetic disorder like sickle cell anaemia.
Evolution:
The gradual change occurring in living organisms over a long duration is called as evolution.
It is very slow going process. At present, crores of species of plants and animals are present on the earth. Animal diversity ranges from amoeba to giant whale. The plant diversity ranges from unicellular chlorella to giant banyan tree.
Theory of Evolution
According to this theory, first living material was formed in ocean. From these unicellular organisms was formed. These unicellular organisms undergone gradual changes and formed multicellular organisms. All these changes were slow and gradual. Duration of all these changes is at least 300 crores years.
Evidences of Evolution :-
1) Morphological Evidences:
Morpholgy is the study of external characters. The similarity in external characters of organisms proves that their origin must be same and must have common ancestors.
Example: The leaves of brinjal, solanum and potato show similarities.
2) Anatomical Evidences:
The study of internal characters is called as anatomy. The study of anatomy helps us to find the relationship different organisms. The similarity in structures of bones and bony joints helps to understand the ancestry of human, cat, bat and whale.
3) Vestigial organs:
The degenerated or underdeveloped useless organs of organisms
are called as vestigial organs. In human being there are about hundred vestigial organs.
Example:- Various vestigial organs like tailbone (coccyx), wisdom teeth & body hairs.
4) Paleontogical Evidences:
The study of fossils is called as paleontology.
Large numbers of organisms get buried due to the disasters like flood, earthquake, volcano etc. The remnants and impressions of such organisms remain preserved underground. These are called as fossils. The study of fossils is very useful to understand the evolution. The age of fossils is determined by carbon dating technique.
Carbon dating technique
Carbon dating technique was developed by Willard Libby. This technique is used to determine the age of the fossils.
1) In living organisms the ratio between C-14 and C-12 is constant.
2) But after the death of organism the decaying process of C-14 occur continuously.
3) So the ratio between C-14 and C-12 changes continuously because C-12 is non radioactive.
4) The time passed since the death of plant or animal is calculated by measuring the radioactivity of C-14 and ratio C-14 to C-12 present in their body.
5) Emryological Evidences:
The study of embryo is called as embryology.
The embryonic developmental stages of fish, salamander, chicken, pig, cow, rabbit and man shows that all embryos show external similarities during initial stages. Similarities in initial stages indicate the common origin of all these animals.
6) Connecting Links:
Some plants and animals show some morphological characters by which they can be related two different groups, hence they are called as
connecting links.
Examples: 1) Platypus lays eggs like reptiles but shows relationship with mammals due to the presence of mammary glands and hairs. It shows connecting link between the reptiles and mammals.
2) Lung fish performs respiration with lungs respective of being fish. It is a
connecting link between the fishes and amphibians.
3) Archaeopteryx fossil shows the connecting links between reptiles & birds.
Darwin’s theory of natural selection
Charles Darwin published the theory of natural selection based on his observations of large number of plants & animals. He published a book titled ‘Origin of species’.
Darwin says that all living organisms reproduce prolifically. All the living organisms compete with each other for food and shelter in life threatening manner. In this, only those organisms sustain which show some modifications. The nature selects only those organisms which are fit to live and rest perish. The selected organisms can perform reproduction and give rise to new species.
Objections on Darwin’s theory
1) Natural selection is not the only factor responsible for evolution.
2) He did not mention about useful and useless modifications.
3) There is no explanation about slow changes and abrupt changes.
Lamarckism :-
Lamarck proposed that morphological changes occurring in living organisms are responsible for evolution. The living organism acquires characters through their lifetime and then these characters are passed to their offspring. This theory is also known as Inheritance of acquired characters or Lamarckism.
Examples:
1) According to this theory snakes have lost their legs by modification for burrowing habit.
2) Wings of birds like ostrich and Emu have become weak due to no use.
Drawbacks of Lamarckism :-
It has been verified many times that modifications brought in us are not transferred to the next generation.
Speciation :-
Formation of new species of animals and plants is called as speciation.
Species is a group of organisms that can produce fertile individuals through natural reproduction. Genetic variation is responsible for formation of new species from earlier ones. Geographical and reproductive changes are also responsible for speciation.
Human evolution ( Evolutionary History of modern man)
1) Ancestors of human developed from animals which resembled lemur like animals.
2) About 7 crores years ago, monkey like animals evolved from them.
3) There after about 4 crores years ago in the Africa the tail of these monkey like animals gradually disappeared.
4) Simultaneously, there was enlargement in their body, brain volume too. The hands also improved and were provided with opposite thumb.
5) These apes like animals gave rise to gibbon and orangutan in the South and North-East Asia and gorilla and chimpanzee stayed in Africa about 2.5 crores of years ago.
6) The climate becomes dry and this resulted into reduction of forest cover. Due to this arboreal apes came on the land and start terrestrial mode.
7) Due to this, there were changes in the lumbar bones and vertebral column. The hands were also freed from locomotion.
8) The first record of human like animal is ‘Ramapithecus’ ape from East Africa.
9) Ramapithecus - Australopithecus - Neanderthal man - Cro-magnon
10) Neanderthal man was said to be the first wise man. The increasing growth of brain made man more intelligent and thinking animal.
Give reasons:
1) Peripatus is said to be a connecting link between Annelida & Arthropoda.
1) Peripatus show segmented body, thin cuticle and parapodia like appendages. These characters are typical of annelids.
2) It also shows tracheal respiration and open circulatory system like arthropods.
3) As peripatus shows the characters of both annelids as well as arthropods, it is said to be the connecting link between Annelida & Arthropoda.
2) Some of the characters of parents are seen in their offsprings.
1) The parental genes are transferred to their progeny through through male and female gametes.
2) These genes carry hereditary characters.
3) As they are transmitted from the parents to their offsprings. Some of the characters of parents are seen in their offsprings
