science note Hereditary and evolutions

Hereditary and evolutions

Heredity: The process of transferring parental characteristics to their offspring is called heredity. 
Genetics:  The branch of biology which deals about mechanism of heredity and variation is called genetics.
ڢ Gregor Mendel is the scientist who studied about the mechanism of heredity. Mendel is called father of genetic.

Mendel took pea plant in the experiment to study about the mechanism of heredity.
Reasons for taking pea plant in the experiment are as follows.

 i) It contains large number of alternating / contrasting character such as tall and draft, round seed and wrinkled seed.
 ii) Their life spam is short.
 iii) It is easy to cultivate.
iv) Artificial cross pollination can be done in pea plant easily.

Mendel’s experiment
 To study about the mechanism of heredity, Mendel took tall and dwarf pea plant. He made artificial cross pollination between tall and dwarf pea plant. In the 1st generation , all the tree plant were found to be tall but they also contain dwarf character. This means tall character is seen in the 1st generation and dwarf character is not seen in the 1st generation. So, tall character is called dominant character and dwarf character is called recessive character.
When the plant of 1st generation were allowed for self pollination. In the 2nd generation , 75% of pea plants were tall and 25% of pea plant were dwarf. This means 25% of pea plant were pure tall, 50% of pea plant were hybrid tall, and 25% of pea plant were pure dwarf.

Let, TT be pure tall pea plant
tt be pure dwarf pea plant  
Phenotypic ratio: 3:1
Genotypic ratio :  1:2:1

Dominant character 
 The characteristic which is expressed (visible) in the 1st   generation is called dominant character.

Recessive character
 The character which is not expressed (visible) in the 1st generation is called recessive character.    E.g. when cross pollination is done between tall and dwarf pea plants. In the 1st generation all the plants are tall. Here, tall character is seen but dwarf character is not seen in the 1st generation. So, tall character is called dominant character and dwarf character is called recessive character. 

Monohybrid cross 
 The cross between parents having single pair of alternating character is called monohybrid cross.
E.g. cross between tall and dwarf pea plant.

Dihybrid cross 
 The cross between the parents having two pairs of alternating character is called dihybrid cross.
E.g. Cross between tall pea plants having red flower with dwarf pea plant having white flower.

Poly hybrid cross  
 The cross between parents having more than two alternating character is called poly hybrid cross.
E.g. cross between tall pea plant having red flower and round seed with dwarf pea plant having white flower and wrinkled seed.

Hybrid 
The organism obtained by cross between the parents of same species having alternating character is called hybrid.

Hybrid tall
 When cross pollination is done between tall and dwarf pea plant. In the 1st generation all the plants are found to be tall but they also contains character of dwarf too. They are called hybrid tall.

Phenotypic 
The external appearance of an organism is called phenotypic.

Genotypic 
The genetic composition of the organism is called genotypic.

Mandel’s law 
 i) Law of dominance
 ii) Law of purity of gametes (Law of segregation of gametes)
 iii) Law of independent assortment

i) Law of dominance
When cross pollination or cross fertilization is done between parents having alternating character, only one character is visible in the 1st generation and other characteristics remains hidden (is not seen) in the 1st generation. The characteristic which is visible in the 1st generation is called dominance character and the characteristic which is invisible in the 1st generation is called recessive character. For e.g. when cross pollination is done between tall and dwarf pea plant in the 1st generation, tall character is express and dwarf character is not express. This means all the plants are found to be tall. So, tall character is dominance character and dwarf character is called recessive character.

ii) Law of purity of gametes 
The genes remaining in the same pair or in different pair get separated during the formation of gamete. For e.g. when cross pollination is done between tall and dwarf pea plant. In the 1st generation, hybrid tall pea plants are obtained due to separation of gametes. In the second generation, 25% of plants are pure tall, 50% of plants are hybrid tall and 25% of plants are pure dwarf due to separation (purity) of gametes.

iii) Law of independent assortments 
 In dihybrid and poly hybrid cross, genes of a pair assort (remains) independently with genes of another pair during the formation of gametes.
For e.g. when cross pollination is done between tall pea plants having round seeds with dwarf pea plants having wrinkled seeds. In the 1st generation, all the pea plants were tall having round seed. In 2nd generation, the pea plant were tall round, tall wrinkled, dwarf round and dwarf wrinkled. It is possible only when f1 generation individual produce 4 types of gametes.
Let TTRR be tall pea plants having round seed. Also let ttrr be dwarf pea plant having wrinkled seed.
Tall round = 9
 Tall wrinkled = 3
 Dwarf round = 3
 Dwarf wrinkled = 1  
  The ratio of plant: Tall round: tall wrinkled: dwarf round: dwarf wrinkled = 9:3:3:1

Variation
 Variation is defined as morphological change in an organism due to genetic or environmental reason.
 Or
 The gradual change in an organism due to genetic or environmental reason.
E.g. If we measure the height of the human beings. Some are tall, some are short and others are intermediate.

Mutation 
 The sudden change (discontinuous change) occurred in an organism is called mutation.
e.g. Newly  borned baby without hand, newly borned baby with  jointed head, six finger in one hand, physical disability.

# Nucleic acid (chemical base of heredity) 
 (DNA and RNA are nucleic acid)

DNA	RNA
i) It is deoxyribonucleic acid.  ii) It is double stranded.  iii) It contains deoxyribose sugar.  iv) It contains 4 nitrogen bases. They are adenine, guanine, thymine and cytosine.  v) It transfer heredity character vi) It is found only in chromosome.	i) It is ribonucleic acid.  ii) It is single stranded.  iii) It contains ribose sugar.  iv) It contains 4 nitro bases. They are adenine guanine, cytosine and Uracil.  v) It helps in protein synthesis.  vi) It is found in chromosomes and in cytoplasm.

Evolution (organic evolution)
             The development of complex form of organisms from simple form due to gradual change is called evolution.
             The evidences (Proof) which supports theory of evolution are as follows:
 i) Evidence form fossils
 ii) Evidence form comparative morphology and anatomy.
 iii) Evidence from embryo (Embryological evidence)
 iv) Evidence from bridge animals
 v) Evidence from vestigial organ.
vi) Evidence from distribution of organism.

  i) Evidence form fossils 
            Sedimentary rocks are formed by continuous depositing and hardening of sediment particles (sands, mud, soil, dead bodies of plants and animals) at the bank and at the bed of sea. So, sedimentary rock has different strata. In this rock, the fossils of simplest form of organisms remain on the lowermost strata and the fossils of higher form of organisms’ remains on the uppermost strata. From the study of fossils of different organisms, it becomes clear that complex form of organisms originated gradually from simplest form of organism.


ii) Evidence form comparative morphology and anatomy.
 This evidence tells that those organisms in which the structure of bones of particulars organ is same, there must be mutual relationship between those organisms.
 E.g. The structure of bones of human hands, forelimbs of horse, bones of whale flap, bones of bat wings are similar. This means these animal might had common ancestors.

iii) Evidence from embryo (Embryological evidence)
 This evidence tells that those organisms which have same type of embryo, there must be mutual relationship between those organism.
For e.g. Initial structure of embryo of hen, human and fish are same. So, these animals might have come from same ancestors.

iv) Evidence from bridge animals.
 The animal whose structure and behavior (characteristics) are partly related to higher animal is called bridge animals.
E.g. duck billed platypus. They lay eggs but have breast like mammals. This indicates they are developing from aves towards mammals. So, bridge animal makes clear that evolution of higher animal might have occurred from lower animals. 

v) Evidence form vestigial organ.

 The organ which are present as reduced structure and are functionless in the body are called vestigial organ. E.g. Vermiform appendix, muscles of external ear, hair on the body, canine teeth etc. These organs have no function in human while in some in small animals they are full functional. For e.g. vermiform appendix in human bodies. Large intestine has no function in human but this part is fully developed and functional in herbivorous animals like cow, rabbit, goat etc. It proves that the animal which have vestigial organ and the animals which still fully use these organs should have been originated from common ancestors. Thus the evidence obtained from vestigial organ proves the theory of evolution.       

vi) Evidence from distribution of organism.
When the organisms of same species are distributed in different parts of the world with different climates, they have to change their certain characteristics in that environment. So, organisms of same species will be quite different from each other even they have same ancestors due to change occurred in their body. For e.g. elephant found in Africa and in India cannot be found in Brazil.

# Darwin theory of evolution 
 Darwin’s theory about the evolution of livings beings is based on following description.
 i) High fertility rate (enormous fertility rate)
 ii) Struggle for existence.
 iii) Variation and heredity
 iv) Natural selection (survival for fittest)
 v) Origin of the species

i) High fertility rate (enormous fertility rate)
Every organism can produce large number of offspring during their life time. So, the population increases in geometric ratios. This means population becomes double in one year, increases four times in second year and becomes eight times in third year. But high fertility rate is balanced by great destruction of organism by nature. So, population approximate remains the same.’
  
ii) Struggle for existence.
Every organism in this world has to fight for food, shelter, and also they have to fight to be protected from enemies and diseases etc. The organism which can fight will be able to survive and other which cannot fight will disappear. So, struggle for existence makes the size of population constant.

iii) Variation and heredity 
The offspring show little differences with their parents and they also differ from each other. This is called variation. The variation obtained by offspring get transfer to the new generation if that variation is useful and successful. In successful generation, the variation becomes their own characters.

iv) Natural selection (survival for fittest)
 The nature determines the period and possibility of survival of living being. The organisms which are able to adjust in the environment can survive. The acquired (obtained) character developed for their adjustment are transferred to their offspring. They developed more in new generation and new types of species are developed .In this way, the organisms having suitable variation can survive and the organism which don’t have suitable variation disappear, it is called survival for fitness.
Or   The selection of more progressive character and elimination of less progressive character by nature is called natural selection.

 v) Origin of the species
The suitable variations are transferred from parents to their offspring. So, the new offspring become successful to adjust in change environment. Sometimes sudden variation occurs in the new offsprings which is called mutation. This causes the evolution of the new species In this way, the origin of various new species occurs from ancestors.

# Lamark’s theory 
 i) Direct environment effect
 ii) Use and disuse of organ
iii) Inheritance of acquired character


i) Direct environment effect 
 The environment directly affects the modification of organ or direct effect the characteristics of organ. There is new need for organism due to change in environment which brings modification of organ or which causes change in character of the organism and new organism will be created due to continuous change. E.g. Yaks found in Himalayan region have thick fur on their body due to influence of extreme cold climate.

ii) Use and disuse of organ
 The development of an organ depends upon its use. The disuse of organs makes the organ makes the organ weak and becomes reduced structure and ultimately gets lost.
 E.g. Snakes haves elongated body due to continuous creeping on land.

iii) Inheritance of acquired character      
 The character obtained by organism by direct environmental effect is called acquired character. The acquired characters are transferred (inherited) from one generation to other generation and new species are originated after the long series of generation. For e.g. initially there were short necked giraffe which used to graze on ground. Due to scarcity of grass, they started to eat leaves of trees. This habit resulted in using neck more and more and in slow increase of neck from one generation to another generation and ultimately giraffe with long neck appeared.

Criticism of Darwin’s theory (Drawback)
 i) He didn’t explain about the presence of vestigial organ in organism.
 ii) It is not always case that useful variation are selected.
iii) He didn’t explain about the origin of variation.

Criticism of Lamark’s theory 
 i) He didn’t prove experimentally that use and disuse of organ can modify organ.
 ii) All the acquired characters are not inherited into new generation.
iii) It is incorrect that new organ can be developed according to need and wish of an organism.