HEREDITY AND EVOLUTION
– Heredity – Variation – genetics
– Mendel’s factor – Chromosome – genes
– DNA
– Structure of Chromosome – Karyotype
– DNA
– Sex Determination
– Organic evolution–evidences – Theories of
Evolution
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In
asexual reproduction, all the off springs are exactly identical to one another
as well as to parents because of same genetic makeup.
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In
sexual reproduction the various off springs are similar to their parents but
are not identical to items or to one another because of genetic various except
IDENTICAL TWINS.
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Identical
Twins: grow from a
single cell which splits after fertilization. Look alike
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Non
Identical twins: Look less
like they grow from 2 different fertilized cells & hence don’t have
exactly same genetic material.
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Heredity:
The transmission of
characters (traits) from the parents to their off springs is called
Heredity.
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Variation:
The differences in the
characters among the individuals of a species is called variation is
necessity for organic evolution.
Both Heredity & variation are fundamental
factors in the process of Evolution of an organism.
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Genetics:
The branch of biology
which studies heredity & variation is called genetic.
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Terms
gene was coined by scientist – Johanssen in 1909.
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Chromosomes:
Chromosomes are thread
like structures present in the nucleus of a cell which contain
hereditary information of the cell. They are made up of DNA & proteins.
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chromatids
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centromere
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Chromosome
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2 chromatids
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1 chromosome
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One species
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fixed no. of chromosome
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Humans
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46 chromosomes = 23 pairs of homologues chromosomes
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1
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LECTURE
NOTES – BIOLOGY
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(Same size and Shape)
Types:
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Metacentric
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Sub–Metacentric
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Acrocentric
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Telocentric
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Dipoid
Cell: A cell which
has the full no. of chromosomes with two of each pair, is called a
diploid us.
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Hiploid
Cell: A cell
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c
half the
no. of chromosomes
with one of
each pair e.g.
gamete
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cell/sex cell.
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Autosomes: All
the chromosomes in
a cell (except
sex chromosomes) are
called
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autosomes.
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Karyotype:
During metaphase stage of
cell division, the chromosomes become shorter, thicker & can be seen
very clearly. In order to study the no. shape, size and type of chromosomes of
an individual, the chromosomes during melaphase, are arranged acc to their
length & position of centromere. Such an arrangement of chromosomes for the
purpose of studying is called Karyotype. Identifying a chromosome thru
microscope, special staming technique called “Banding Technique” is used.
Study of
karyotype of an individual helps in the diagnosis of genetically disorders.
Down’s
Syndrome: Any variation
in the no. of chromosomes from the normal no or any change in the shape
of chromosome during fertilization can lead to severe abnormality or disorder
in the child after birth which are called Genetic / Heredity Disorder
e.g. Down’s syndrome which is caused by interitance of an extra 21st chromosome.
In this syndrome, full mental development does
not take place.
Symptoms: Mental retardation, Flattened , nose,
Defective ears, widely separated eyes, short & broad neck, protruding
tongue, small & sturdy hands widely.
Gene: Gene is the unit of inheritance.
Various genes are located in the chromosomes at
fixed position genes are responsible for our characteristic features.
Chemically gene is a segment of a large
polynucleotide molecule called deoxyribonucleic acid
DNA: Dexyribo nucleic acid
DNA was first isolated by Frederick meisher from
the nucleus of the pus cells. It is acidic in nature so the name is nucleic
acid.
DNA is a macromolecule/polymer which is made up
of a large no. of smaller units called Nucleotide.
So DNA is a polynucleotide. Nucleotide is the basic structure unit of
DNA.
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Components of a Nucleotide:
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A
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Purines
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1.
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a nitrogen containg base
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G
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2.
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a pentose sugar
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C
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3.
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a phosphate gp
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Purimidiness
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T
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Any one of nitrogen base pairs up only c a specific nitrogenous base of the opposite
side. Such specific pairing is called COMPLIMENTARY PAIRING.
(Cytosome) C pairs up c G
(Guanine)
DNA
molecule is like that of a spiral staircase in which both the railing of the
staircase are made of sugar & phosphate molecules alternative each other
and held together by strong chemical bonds whereas the steps of the staircase
are made of complimentary nitrogenous bases held together by weak bonds.
N.B.: DNA structure established by Wastson & Crick
in 1953.
Each helical turn of the DNA molecule has a
length of 3.4 nm in which 10 nucleotide units are present.
Pentose sugar
Phosphate gp
A – Adenine
T – Thymine
C – Cytosine
G –
Guanine
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A
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T
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Complimentary parsing
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B
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G
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Genetic
Engineering: The
technique for altering an organisms genetic make up inserting genes from
other organism its chromosomes is called Genetic Engineering.
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Sex
Determination: The process
by which the sex of a per is determined is called sex determination.
The Chromosomes which determine the sex of a
person called sex chromosomes which are
of 2 types X & Y.
Males Female
X
& Y X X
XX XY Zygote
(Male
Child)
(Female Child)
Q
XX
combination is always found in females XY combination is always found in males.
So it is the sperm
(carrying either X or Y) which determines the sex of a child
ORGANIC EVOLUTION
Evolution is the sequence of gradual changes
which take place in the primitive organisms over millions of yrs. In which non
species are provided.
Some imp. Sources which provide evidence for
organic evolution are
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Fossils
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Homologus organs
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Analogus organs
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Vestigial organ
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Embryology
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Homologus
organ: Organs having
similar basic structure & origin but different functions e.g.
porelnubs of a frog, birds & man.
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Analogous
organs: The organs
with different basic structure but have similar appearance &
performs similar functions.
e.g. wings
of an insect & a bird.
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Vestigial
organs: Organs which
are functionless useless but were functional in aucestors e.g. Vermiform
appendix Nietuting membrame.
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Embrgology:
The study of the
development of the embryo of an animal is called Embrgoloy.
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Biogenetic
law: It states chat
“Ontogeny recapitulates Phylogeny”
It means
that during the development of the embryo of any organism, its complete
evolutionary history is repeated.
THEORIES OF EVOLUTION
1. Lamarckism 2. Darwinism 3. Synthetic Theory of
Evolution
1.
Lamarckism:
It states
(a) The use & disuse of an organ by an organism
leads to acquiring of variation in the features of that organ.
(b) These variations (acquired characters) are
inherited by the offsprings.
(c) This leads to evolution
This theory was criticsed by August weismann who
ejected the idea of inheritance of acquired characteristics.
DARWINISM / Theory of Natural Selection
(a) All the species produce a large no of offsprings
but population remains fairly constant due to struggle bt the members of same
species & different species for food, space & mate
(b) This struggle eliminates the unfit individuals.
(Survival of the fittest)
(c) This gives orgin to variations which pass into
progeny & over a long period of time, leads to origin of new species.
Limitations: It could not explain how the variations arise.
Synthetic Theory of Evolution:
The most accepted theory these a days which says
that “origin of species is based on the interaction of genetic variation &
natural selection’.
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