இந்தக் கட்டுரையில், TNPSC குரூப் 1, குரூப் 2, குரூப் 2A, குரூப் 4 மாநிலப் போட்டித் தேர்வுகளான TNUSRB, TRB, TET, TNEB போன்றவற்றுக்கான முறைகள் இலவசக் குறிப்புகளைப் பெறுவீர்கள்.தேர்வுக்கு தயாராவோர் இங்குள்ள பாடக்குறிப்புகளை படித்து பயன்பெற வாழ்த்துகிறோம்.
Evolution and Genetics
Evolution:
Biological origin of life:
There are many opinions regarding the appearance of creatures.
All living things on earth have many similarities in structure and
characteristics.
These, such diverse organisms in the past themselves to the evidence.
Organism’s origin, universe’s origin, glory origin and the origin of solar
system were looked upon as a set.
Theories:
There are many theories about the origin of life. Some of them are
1. The theory of special creation:
This theory was published by Hebrew et al.
Suarez was a large supporter of this theory.
The sudden nature of advanced energy vectors was said to be the origin of
organisms.
2. Destruction theory:
The leading scholar of this theory was George Cowier.
According to this, the formation of organisms is said to have been caused by
some geological disturbances.
3. Biological theory:
It was asserted by the Greek scientists Thales Plato and Aristotle.
Thus organisms are said to have evolved from inanimate objects.
4. Theory of life:
This was emphasized by Louis Pasteur.
Thus life is said to have originated from living things.
5. Modern theory of the origin of life:
Heckle emphasized this theory.
This concept is described in detail in the theory of chemical evolution by
Opparin and Halden Ponro.
Opperin published the book, “The Origin of Creatures” in 1938.
In this book he describes the origin of life.
Evidence of Evolution:
Father of Evolution – Charles Darwin
The father of ideas about evolution – Empedocles.
Herbert Spencer was the first to use the term evolution.
The word evolution means flowering (or) expansion.
Human evolution:
Chimpanzees – had human bodies.
Hominids – People who lived in East Africa. They ate fruits and had a steady walk.
Homo habilis – Human nature.
Homo erectus – carnivores.
Neanderthal – lived in Asia (1 million years ago).
Archie Homo sapiens – Frozen humans.
Homo sapiens – modern humans.
Evidence of evolution:
1. Archaeological evidence:
The field of science that helps to learn about fossils is called archaeology
(paleontology).
Father of archaeology was Leonardo da Vinci.
Huxley points out that the dead bodies of prehistoric plants and animals turn
into bacilli.
2. Types of tombstones:
The whole body of the creature is buried intact e.g. Bones of humans
Carbolites:
The waste products excreted from the animal’s body are hardened and found
in small pieces.
3. Evidence of organ analogy:
The elements are similar in basic structure but used for different functions.
In mammals, the forelegs of human, horses and birds have the same skeletal
structure, but their function is different.
4. Active similar elements:
Elements that have different elements in a system that perform the same
functions e.g. Butterfly wing, bat wing.
5. Residual elements:
Humans have 180 residual organs. These are inactive.
E.g. Auricular muscles – those that help to move the ear.
6. The rest of the antecedent attribute:
The sudden appearance of certain traits that were seen many times before.
Appearance of dense hairs all over the body.
7. Instrumental evidence:
Sensing the development of the mature organism from the eggs.
Lamarckism
Jean Baptiste de Lamarck (1744 – 1829) is well known for his theory of
evolution.
In 1809 he published his book titled ‘Philosophie Zoologique’.
This book contains his views on evolutionary mechanisms.
The theory of evolution as proposed by Lamarck is popularly known as the
‘Theory of inheritance of Acquired Characters’.
According to this theory modifications or changes acquired during the
lifetime of an organism can automatically be transmitted to succeeding
generations.
While elaborating this theory, Lamarck advanced four laws or propositions.
1. Law (or) Proposition
‘In evolution, during course of time, organisms or their component parts
gradually tend to increase in size.
Lamarck cited the evolution of horses as an example to explain this law.
2. Law or Proposition
‘If an organism is ‘in need’ of an organ, sooner or later it will arise.
This view of Lamarck emphasized the significance of mind and its thinking
being related to needs in an environment.
Thus, according to Lamarck a continuous thinking for several generations
can lead to the origin of an adaptive character.
Lamarck elaborated his view citing the lengthening of neck in giraffe over
the years.
3. Law (or) Proposition – Law of use and disuse
According to this law, constant use of an organ changes its efficiency and
makes that organ to increase in size with better development.
Similarly if an organ is not used for a long time, it might lead to reduction
in efficiency and size of that organ.
4. Law (or) Proposition. Inheritance of Acquired Characters
‘Bodily changes or new characteristics obtained by an organism during its
life time will automatically get transferred to the next generation’.
While proposing this law, Lamarck did not provide any specific example.
The IV Law of Lamarck had been subjected to severe criticisms. Several
experiments had been carried out, either to prove or disprove this concept.
In 1890, the German Scientist, August Weismann performed some
experiments with the rats.
This lead to the formulation of the ‘Germplasm theory’ which states that
‘any change to the somatoplasm will not have
Neo-Lamarckism
Lamarck’s ‘theory of inheritance was further studied by a group of
scientists.
Their ideas supporting Lamarck’s opinion collectively constitute Neo-
Lamarckism.
McDougall (1938) tried to prove that learning is an acquired character
that can be inherited. He did his experiments on rats.
However, the controversy over ‘inheritance’ of acquired characters still
continues.
This theory of Lamarck while has not been disproved totally, it remains to
be proved correct.
Darwinism
Darwinism comprises the natural selection concept as advanced by Charles
Robert Darwin in 1859.
His theory provided the correct idea to explain all processes and intricate
mechanisms of evolution.
The theory of natural selection is considered on par with Newton’s law of
gravitation and Einstein’s theory of relativity.
The monumental work of Darwin was titled as “The Origin of species”
The book of Darwin convincingly demonstrates the fact of evolution.
Further, it elaborates on the theory of natural selection as a convincing
mechanism for providing evolutionary transformations.
While Darwin prepared his work for publication, a similar idea to explain
evolution was proposed by another naturalist, Alfred Russel Wallace
(1823-1913) from Malay Archipelago.
Charles Darwin gracefully accepted for the publication of his theory as a
joint paper with Wallace.
Thus the theory of natural selection is actually titled as ‘Darwin-Wallace
theory of evolution’.
The Theory of Natural Selection
1. Overproduction or Prodigality of nature
All living beings have an innate desire to reproduce and form their own
progeny.
In this attempt they have the capacity to multiply in a geometrical manner.
Such an enormous reproductive potentiality can be observed in all species of
organisms.
For example a single female salmon fish can produce 28,000,000 eggs in a
season.
2. Struggle for existence
According to Darwin while the population increases in geometric ratio
there is no corresponding increase in food production.
This causes an intensive struggle for living.
3. The universal occurrence of variations
The occurrence of variations is a characteristic feature of all groups of
animals and plants.
The variations may be morphological, anatomical, physiological or
behavioral.
4. Survival of the fittest
While all living organisms face the struggle for existence, certain
organisms possessing adequate modifications are able to escape and
survive.
Such modifications are due to inherent variations.
Hence favorable variations make an animal or a plant to be successful in
life.
5. Natural Selection
According to Darwin ‘the fittest’ forms that are allowed to survive are
chosen by ‘Natural Selection’.
The forces of natural selection will encourage only those that have suitable
variations as adaptive features, to survive.
Darwin designated them as ‘fittest’ forms.
Darwin strongly believed that using the natural selection concept, all
evolutionary processes in the living world can be explained.
Genetics:
Mendel’s Monohybrid Cross:
Gregor Johann Mendel – Father of Genetics
Mendel (1822-1884) was an Austrian monk who discovered the basic
principles of heredity through his experiments.
His experiments are the foundation for modern genetics.
In his leisure time he started his famous experiments on the garden pea
plant.
Mendel noted that they differ from one another in many ways.
Thus Mendel had chosen 7 pairs of contrasting characters for his study as
shown in the table:
Characteristic
studied
Dominant character Recessive character
Seed shape Round Wrinkled
Seed colour Yellow Green
Flower colour Blue White
Pod shape Inflated Constricted
Pod colour Green Yellow
Flower Position Axillary Terminal
Stem length Long Short
Monohybrid Cross- Inheritance of One Gene:
Crosses involving inheritance of only one pair of contrasting characters are
called monohybrid crosses.
Mendel’s Explanation of Monohybrid Cross:
Parental generation: pure breeding tall plant and a pure breeding dwarf
plant.
F1 generation: Plants raised from the seeds of pure breeding parental cross
in F1 generation were tall and monohybrids.
F2 generation: Selfing of the F1 monohybrids resulted in tall and dwarf
plants respectively in the ratio of 3:1.
External expression of a particular trait is known as phenotype.
So the phenotypic ratio is 3:1.
In the F2 generation 3 different types were obtained:
Tall Homozygous – TT (pure) – 1
Tall Heterozygous – Tt – 2
Dwarf Homozygous – tt – 1
So the genotypic ratio 1:2:1.
A genotype is the genetic expression of an organism.
Mendel’s Interpretation on Monohybrid Cross:
Based on these observations it was confirmed by Mendel that ‘factors’ are
passed on from one generation to another,
now referred to as genes.
Tallest and dwarfness are determined as (T) dominant character. Factor
for dwarfness determined as (t) – recessive character.
If the factors are the same as the parents, they are also called homozygous.
If they are unlike (Tt) they are referred to as heterozygous.
Two factors making up a pair of contrasting characters are called alleles
or allelomorphs. One member of each pair is contributed by one parent.
When two factors for alternative expression of a trait are brought
together by fertilization only one expresse s itself, (tallness) masking the
expression of the other (dwarfness).
The character which expresses itself is called dominant condition and
that which is masked is called recessive condition.
The factors are always pure
When F1 hybrids are self-crossed the two entities separate and then unite
independently, forming tall and dwarf plants.
Dihybrid Cross:
Inheritance two Genes and Law of Independent Assortment:
The two pairs of contrasting characteristics chosen by Mendel were
shape and color of seeds: round-yellow seeds and wrinkled-green
seeds.
Mendel crossed pea plants having round-yellow seeds with pea plants
having wrinkled-green seeds. Mendel made the following observations:
Mendel first crossed pure breeding pea plants having round-yellow seeds
with pure breeding pea plants having wrinkled- green seeds.
And found that only round-yellow seeds were produced in the first
generation (F1).
No wrinkled-green seeds were obtained in the F1 generation.
From this it was concluded that round shape and yellow color of the
seeds were dominant traits over the wrinkled shape and green color of
the seeds.
When the hybrids of F1 generation pea plants having round-yellow seeds
were cross-bred by self-pollination.
Then four types of seeds having different combinations of shape and
color were obtained in second generation or F2 generation.
They were
round yellow (9),
round-green (3),
wrinkled yellow (3)
wrinkled-green seeds (1)
The ratio of each phenotype (or appearance) of seeds in the F2 generation is
9:3:3:1. This is known as the Dihybrid ratio.
From the above results it can be concluded that the factors for each
character or trait remain independent and maintain their identity in the
gametes.
The factors are independent to each other and pass to the off springs
(through gametes).
Results of a Dihybrid Cross:
Mendel got the following results from his dihybrid cross
1. Four Types of Plants: A dihybrid cross produced four types of F2
offsprings in the ratio of 9 with two dominant traits, 3 with one dominant
trait and one recessive trait, 3 with another dominant trait and another
recessive trait and 1 with two recessive traits.
2. New Combination: Two new combinations of traits with round green and
wrinkled yellow had appeared in the dihybrid cross (F2 generation)
Genetic Disorders:
A genetic disorder is a disease or syndrome that is caused by an abnormality
in an individual DNA.
Abnormalities can range from a small mutation in a single gene to the
addition or subtraction of an entire chromosome or even a set of
chromosomes.
Geneticdisorders are of two types namely, Mendelian disorders and
chromosomal disorders.
Thalassemia:
Thalassemia is an auto somal recessive disorder.
It is caused by gene mutation resulting in excessive destruction of RBC’s
due to the formation of abnormal haemo globin molecules.
Thalassemia is classified into alpha and beta based on which chain of
haemoglobin molecule is affected.
It is controlled by two closely linked genes HBA1 and HBA2 on
chromosome 16.
Beta Thalassemia is the most common type of Thalassemia and is also
known as Cooley’s anaemia.
In this disorder the alpha chain production is increased and damages the
membranes of RBC.
Phenylketonuria:
It is an inborn error of Phenylalanine metabolism caused due to a pair of
autosomal recessive genes.
It is caused due to mutation in the gene PAH (phenylalanine hydroxylase
gene) located on chromosome 12 for the hepatic
enzyme “phenylalanine hydroxylase”.
It is characterized by severe mental retardation, light pigmentation of skin
and hair.
Albinism:
Albinism is an inborn error of metabolism, caused due to an autosomal
recessive gene.
Melanin pigment is responsible for skin colour.
Absence of melanin results in a condition called albinism.
In an albino, melanocytes are present in normal numbers in their skin, hair,
iris, etc., but lack melanin pigment.
Huntington’s chorea:
It is inherited as an autosomal dominant lethal gene in man.
It is characterized by involuntary jerking of the body and progressive
degeneration of the nervous system, accompanied by gradual mental and
physical deterioration.
The patients with this disease usually die between the age of 35 and 40.
Chromosomal Abnormalities:
Each human diploid (2n) body cell has 46 chromosomes (23 pairs).
Chromosomal disorders are caused by errors in the number or structure of
chromosomes.
Chromosomal anomalies usually occur when there is an error in cell
division.
Autosomal aneuploidy in human beings:
Several autosomal aneuploidies have been reported in human beings.
E.g. Down’s syndrome (21-Trisomy), Patau’s syndrome (13-Trisomy).
1. Down’s Syndrome/Trisomy – 21:
Trisomic condition of chromosome – 21results in Down’s syndrome.
It is characterized by severe mental retardation, defective development of
the central nervous system, mouth is constantly open and the tongue
protrudes.
2. Patau’s Syndrome/Trisomy-13:
Trisomic condition of chromosome 13 results in Patau’s syndrome.
Small head with small eyes, cleft palate, malformation of the brain and
internal organs are some of the symptoms of th is syndrome
Allosomal abnormalities in human beings:
Mitotic or meiotic non-disjunction of sex chromosomes causes allosomal
abnormalities.
1. Klinefelter’s Syndrome (XXY Males):
This type of genetic defect is caused by the addition of an X chromosome in
men.
Persons with this syndrome have 47 chromosomes (44AA+XXY).
They are usually sterile males, tall, obese, with long limbs, high pitched
voice, under developed genitalia and have feeble breast (gynaecomastia)
development.
2. Turner’s syndrome (XO Females):
This genetic disorder is due to the loss of a X chromosome resulting in a
karyotype Persons with this syndrome have 45 chromosomes (44
autosomes and one X chromosome) (44AA+XO) and are sterile females.
Low stature, webbed neck, under developed breast, rudimentary gonads
lack of menstrual cycle during puberty, are the main symptoms of this
syndrome.
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