Origin of life
1. Spontaneous generation - abiogenesis
Proposed by Aristotle. According to this theory life, originates spontaneously from lifeless matter or non-living things
Eg:- Fishes originated from mud, insects from decaying meat, frogs from moist soil etc.
Louis Pasteur, by his swan-necked flask experiment proved that abiogenesis is not true
(ii) Biogenesis:- Proposed by Fransisco Redi. According to this theory life originates from pre-existing life only. This theory was also supported by Spallanzani and Louis Pasteur
Cosmic theory / Theory of panspermia - proposed by Ritcher
According to this theory the life is distributed through out the cosmos in the form of resistant "spores" or "seeds" known as cosmozoa. These cosmozoa reached the earth and on getting favourable condition, they developed in to organism.
GENETIC POLYMORPHISM
The occurrence of two or more different forms of an organism in the same species or population is called polymorphism.
Features of polymorphism
1. It is the presence of two or more morphological Froms in a species
2. It is due to the existence of different types of genotypes
3. It helps the species to survive efficiently in a variety of environments.
4. The different forms are adapted to the different environments. Each of which is superior in a particular habitat.
Eg:- Blood group of man- Based on blood groups, there are four morphs such as type A, type B, type AB, and type O. All these are determined by different genotypes
Balanced polymorphism
The preservation of genetic variability by heterozygosity is called balanced polymorphism
Eg:- Sickle cell anemia
In man the production of haemoglobin is controlled by the dominant genes - HbA HbA. When this genes are present in the recessive condition ie, HbsHbs, an abnormal haemoglobin is produced and the result is sickle cell anemia. The heterozygous condition ie, HbAHbs do not produce any harm. Moreover a heterozygous individual is not infected by malaria, because the sickle shaped RBC kill the malarial parasite which enter into it. Thus the heterozygous individuals are resistance to malaria.
Species:-
Species are the groups of actually potentially interbreeding natural population that are reproductively isolated from other such groups. It is the basic unit of classification the salient features of a species.
1. Species is amendelian population or a biological unit.
2. Members of species possess distinct morphological features.
3. The memvers of a species are reproductively isolated from other species.
4. The members interbreed among themselves.
5. They share a common gene pool
Sub - species
It is defined as geographically isolated population of a species, which are capable of interbreeding and produce fertile hybrids.
Eg:- The bird golden whistler pachyce phala - pectoralis.
Sibling species
Morphologically similar but reproductively isolated species is known as sibling species. Eg:- Drosophila pseudoobseura and Drosophila persimilis, the two species of fruitfly (Drosophila) do not cross-fertilize.
Speciation
The process of formation of new species is called speciation. There are allopatric speciation and sympatric speciation
1. Allopatric speciation
When two populations inhabit geographically or spatially separated ares, they are called allopatric population. The evolution of such populations into separate species is called sympatric speciation.
Isolation
The segregation of populations into smaller units sections to prevent interbreeding is known as isolation. It is classified them into reproductive isolation and geographic isolation.
Reproductive isolation
Any genetically determined agency that prevents in tebreeding is called reproductive isolation. The reproductive isolation may be of two types. They are premating or prezygotic isolation and postmating or postzygotic isolation Reproductive isolation results sympatric speciation.
a. Pre-mating isolation
This is the external reproductive isolation which prevents inter specific mating. It includes seasonal isolation, eclogical isolation etc.
b. Post-mating isolation
This is the internal reproductive isolation which reduces the formation of zygotes or hybrids. It is due to zygote mortality, hybrid sterility etc.
Geographical isolation
In this isolation, two populations are separated by some barriers such as mountain ranges, deserts, thick forests land bridges or water connections etc. Geographical isolation results in allopatric speciation.
Homologous organs and homology
The organs which are fundamentally similar in structure and origin but adapted for different functions are called homologous organs and this phenomenon is called homology
eg:- Whale’s flipper bat’s wing horse’s foot, cat’s paw, and the human hand. All these perform different function and look superficially different, but are constructed on the same plan
Such homologous anatomical structure implies a common ancestry.
The origin of homologous organs due to adaptive radiation from a common ancestor, is known as divergent evolution
Analogous organ and analogy
The organs which have similar function but differ in structure and origin are called analogous organs and this phenomenon is called analogy are analogous organs. The origin of analogous organs due to adaptations for life in similar habits, is known as convergent evolution.
Vestigial organs
The organs which are non-functional in the pre-sent day animals but were functional in their ancestors and in related animals, are called vestigial organs
Eg:- Vermiform appendix, nictiating membrane, muscles of external ear, coccyx, wisdom teeth, body hair in male etc.
Genetic drift
The random changes in the allele frequency occuring by chance in small populations are called genetic drift. It was described by sewall - wright in 1931. Hence it is all so called Sewall - wright effect. Due to genetic drift some genes are preserved or destroyed irrespective of their quality in small population..
Hardy Weinberg Equilibrium
Proposed by G.H. Hardy and W-Weinberg, which states that in a large population, the gene frequencies of various kinds of gene, remain constant generation after generation if matiny is at random and in the absence of evolutioning forces like mutation, selection and migration. This Hardy-Weinberg is also known as Hardy-weinsberg equilibrium because the gene frequencies in a population are maintained in a state of equilibrium. Evolution occurs only when this equilibrium is upset ie evolution is a departure from Hardy - Weinberg Equilibrium.
Palaeontological evidences
Fossil is the dead remains of the past. It include bones teeth shells and other hard parts and also impressions or imprints left by some previous organs. Fossils are the direct and concrete evidences of evolution. It is also regarded as the written documents of evolution. The process of preservation of organisms or their parts in the form of fossils is known as fossilisation.
The study of fossil is called paleantology it includes plaeozoology (fossil Animals) and paleobotany any (fossil plants). Leonardo da Vinci is considered as the father of palaeontology.
Significance of fossils
2. They help to study the structure, form traits and behaviour of extinct animals .
3. They given an idea above the form and structure of extinct animals
4. They help to study the phylogeny (evolution any history race history) of some Animals such as horse, camels, man etc.
5. Fossils indicate the connecting link between two groups of organisms.
For eg:- Archaeopterix, the fossil bird shows the features of both reptiles and birds. Therefore the connecting with link between birds and reptiles.
6. The time in history when different species were formed or became extinct can be inferred through the analysis of the distribution of fossils in different strait of rocks.