Heredity and Evolution

LECTURE NOTES – BIOLOGY STEPS … A TCY Program _______________________________________________________________________________________

STEPS____________________________________________________________ G e t f r e e c h a p t e r w i s e t e s t s f o r C l a s s X t h o n

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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

• In asexual reproduction, all the off springs are exactly identical to one another as well as

to parents because of same genetic makeup.

• 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.

• Identical Twins: grow from a single cell which splits after fertilization.

Look alike

• Non Identical twins: Look less like they grow from 2 different fertilized cells & hence

don’t have exactly same genetic material.

• Heredity: The transmission of characters (traits) from the parents to their off springs is

called Heredity.

• 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.

• Genetics: The branch of biology which studies heredity & variation is called genetic.

• Terms gene was coined by scientist – Johanssen in 1909.

• 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.

Chromosome

2 chromatids = 1 chromosome

One species = fixed no. of chromosome

Humans = 46 chromosomes = 23 pairs of homologues chromosomes

chromatids

centromere



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(Same size and Shape)

Types:

• Dipoid Cell: A cell which has the full no. of chromosomes with two of each pair, is called

a diploid us.

• Hiploid Cell: A cell c half the no. of chromosomes with one of each pair e.g. gamete

cell/sex cell.

• Autosomes: All the chromosomes in a cell (except sex chromosomes) are called

autosomes.

• 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.

Metacentric Sub–Metacentric Acrocentric Telocentric




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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.

Components of a Nucleotide:

1. a nitrogen containg base

2. a pentose sugar

3. a phosphate gp

Any one of nitrogen base pairs up only c a specific nitrogenous base of the opposite side. Such

specific pairing is called COMPLIMENTARY PAIRING.

(Adenine) A pairs up c T (Thymine)

(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.

• Genetic Engineering: The technique for altering an organisms genetic make up inserting

genes from other organism its chromosomes is called Genetic Engineering.

• Sex Determination: The process by which the sex of a per is determined is called sex

determination.

Purines

Purimidiness

G

A

T

C

Pentose sugar

Phosphate gp

A – Adenine

T – Thymine

C – Cytosine

G – Guanine

AB

TG

Complimentary parsing



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The Chromosomes which determine the sex of a person called sex chromosomes which are

of 2 types X & Y.

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

• Fossils • Homologus organs

• Analogus organs • Vestigial organ

• Embryology

• Homologus organ: Organs having similar basic structure & origin but different functions

e.g. porelnubs of a frog, birds & man.

• Analogous organs: The organs with different basic structure but have similar

appearance & performs similar functions.

e.g. wings of an insect & a bird.

• Vestigial organs: Organs which are functionless useless but were functional in aucestors

e.g. Vermiform appendix Nietuting membrame.

• Embrgology: The study of the development of the embryo of an animal is called

Embrgoloy.

• 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

Males Female X & Y X X XX XY Zygote (Male Child) (Female Child)




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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’.

Heredity and Evolution

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