Concept of neo Darwinism postulate of neo Darwinism

1. Assignment Of
Evolutionary Biology And
Biodiversity
 Topics – Neo-Darwinism
 Natural selection
 Mutation And Recombination
Presented By- Sakshi

2. Neo-DarwinismNeo-Darwinism is a modified version of
the theory of natural selection and is
a sort of reconciliation between Darwin
and de varies theory.
Scientist contributed to this theory –
Huxley,
R.A.Fischer
etc.

3. Postulates of Neo-Darwinism
1. Genetic variability – variability is an opposing
force to heredity.
 Forms the raw material for evolution.
Various sources of genetic variability-
1. Chromosomal aberrations- Morphological changes in
chromosomes without affecting their number.
o These are of four types-
A. Deletion – loss of gene block from chromosome.
B. Duplication – presence of some genes more than once.

4.  C. Translocation- transfer of gene block from one chromosome to other.
 D. Inversion- rotation of intercalary gene block through 180 degrees.

5.  2. Numerical chromosomal changes-
 a. Eulpoidy – gain or loss of one or more genome. It may be-
Haploidy or polyploidy
 b. Aneuploidy- gain or loss of one or two chromosomes. It may
be hypoploidy and hyperploidy.

6. 3. Gene Mutations- invisible changes in the chemical nature of the
gene. These include- Point mutation.
.Gross mutations.
Deletion.
Addition.
Substitution.
 4. Recombination of genes- new combination of genes are formed
due to crossing over , chance arrangement of the bivalents during
metaphase and chance fusion of gametes.
 5. Hybridization- the interbreeding of two different individuals to
produce hybrids.
 Introduces genes from one species to the gene pool of other species.

7. 6. Mutagens- physical and chemical agents used to induces
mutations artificially.
A. chemical mutagens- such as base analogues , methylating agents ,
acridine dyes etc.
B. Physical mutagens- such as temperature, x-rays ,uv-rays etc.
 7. Genetic Drift- change in the gene frequency of small breeding
population due to bottle neck and founder effect.
 FOUNDER EFFECT-


 8. Immigration- introduces many genes in the existing gene pool by
cross breeding between the native individuals and immigrants.

8. 2. Natural selection-
Does not operate on survival of the fittest.
Operates through Differential Reproduction and comparative reproductive
success.
 Differential Reproduction- members which are better adapted to
environment reproduce at a high rate and produce more offsprings than the
members which are less adapted.
 Due to sexual communication, there is free flow of genes and the genetic
Variability spreads from individuals to deme then to population and finally in
most of the members of species.
 So, natural selection causes progressive changes in the gene frequency.
Frequency of more adaptive genes increases and that of less adapted gene
decreases.

9. Example Of Natural Selection- Industrial Melanism.

10. 3. Reproductive Isolation- the inability of living
organisms to interbreed.
Maintains distinctivnesss of characters
among species.
 1. Mechanical isolation- due to the difference in the morphology of genitalia or
reproductive organs.
 2. Geographical Isolation- due to physical factors like sea, mountain, deserts
etc.

11. 3. Spatial isolation- individuals are isolated by long
distances.
 4. ecological or habitat isolation- due to differences in their
habitat.
 5.Temporal Isolation- due to difference in the breeding periods
in different seasons of the year.
 6. Ethological or Behavioural isolation- due to behavioural
differences between individuals of different species during
courtship.

12. 7. Genetic Isolation – due to inter specific sterility due to
accumulation of independent gene mutations for structural and
functional characters.
 8. physiological Isolation- due to functional incompatibility in
their mating or in production , fertilization and survival of the
gametes.

13. So according to Neo Darwinism, 4 steps of
organic evolution are-
 1. Appearance of genetic variability in certain members of a
population.
 2. Spread of genetic variability over population by differential
reproduction.
 3. Some sort of reproductive isolation between elementary
species and the parental species.
 4. Accumulation of genetic variability leads to speciation.

14. NATURAL SELECTION
 The process by which comparatively better adapted individuals out
of a heterogenous population are favoured by the nature over the
less adapted individuals.
Mechanism-
 It operates through differential reproduction.
Differential reproduction states that the individuals which
are better adapted to environment reproduce at a higher rate and
produce more offsprings than the individuals which are less adapted.
So contribute more to the gene pool.

15.  Due to sexual communication there is free flow of genes and
the genetic variability which appears in certain individuals
spreads from one deme to other and to population and finally
in most of the members of the species.
 So natural selection causes progressive changes in the gene
frequencies. The frequency of the more adaptive gene increases and
that if less adapted gene decreases.

16. Examples Of Natural Selection-
1. Industrial melanism-

17. 2. Sickle cell anemia-
 Persons with sickle cell anemia are found in the tropical areas of the
Africa where malaria is very common because sickle shaped cell kill
the malarial parasite.
 Thus natural selection has preserved it along with the normal
haemoglobin in the malaria affected areas.

18. Types Of Natural Selection-
1. Stabilizing or Balancing Selection-
 Under stabilizing selection, extreme varities from both the
ends of frequency distribution are eliminated.
 Favours the average or normal phenotype.
 Bell shaped curve.
E.g.- sickle cell
Anemia.

19. 2.Directional Selection-
 Population changes towards one particular direction along
with the change in environment.
 Individuals at one extreme are eliminated while individuals
at the other extreme are favoured. E.g.- Industrial
melanism, DDT resistant mosquitoes.

20. 3. Disruptive Selection-
 Favours extreme expression of certain traits to increase the
variance in the population.
 Breaks a homogeneous population into many adaptive forms.
 Results in balanced polymorphism.

21. Example of disruptive selection-

22. RECOMBINATION
 Recombination is the process by which two DNA molecules exchange
genetic information resulting in the production of new combination
of alleles.
 It creates the genetic diversity at the level of genes and leads to
variation.

23.  In eukaryotic cell the, recombination occurs during the
pachytene substage of meiosis1.
Recombination may also occur during mitosis in eukaryotes ,
where it ordinarily involves the two sister chromosomes forms
after chromosomal replication.
Types of Recombination
1. Homologous Recombination
 Genetic recombination in which nucleotide sequences are
exchanged between two similar or identical DNA
molecules.

24.  Mostly used by the cells to accurately repair harmful
breaks that occur on both strands of DNA known as
double strand break.
No net gain or loss of nucleotides.

25. HOLIDAY JUNCTION
 Corresponding strands of two aligned homologous DNA duplexes
are nicked by Endonuclease.
 The nicked strands cross over to pair with the nearly
complementary strands of the homologous duplex after which
the nicks are sealed with the non sister chromatid of the
homologous chromosome with the help of the enzyme Ligase.

26. 2.NON-HOMOLOGOUS OR ILLEGITIMATE
RECOMBINATION-
 Occurs in the region where no large scale sequence similarity
is apparent.
3.SITE-SPECIFIC RECOMBINATION-
 Occurs between particular short sequences about 12-24kb.

27.  Takes place in the segments of DNA strands possessing
only limited degree of sequence homology.
4. REPLICATIVE RECOMBINATION-
A type of recombination which generates new copy
of the segment of DNA.

28. RECIPROCAL RECOMBINATION-
 Equal exchange of genetic information.
 Resulting in new DNA molecules that carry the genetic information
derived from both the parents.
 The number of alleles remain the same only their arrangement has
changed.
NON-RECIPROCAL RECOMBINATION/ GENE
CONVERSION-
 One way transfer of the genetic information.
 Number of alleles has changed.
 Transfer of the genetic material from a donar to a highly homologous
acceptor sequence.

29. ADVANTAGES
 1.Enhances genetic diversity in a population –like new gene or allele
combination.
 2. Negative selection can remove deleterious alleles from a
population without removing the entire chromosome.
 3.Ensures proper segregation of homologous chromosome.
 4.Ensures the genetic stability of organism.
 5. Site specific recombination system are potent modifiers.
 6.It is used to map the genes on chromosome as the recombination
proportional to the distance between the genes.
 7.Used for making transgenic cells and organism.

30. MUTATION
 Sudden heritable changes in the genetic material or character of
organism.
 Individuals showing mutation are called mutant.
 The agents causing mutation are called mutagens.
TYPES OF MUTATIONS
1. SPONTANEOUS MUTATION-
Occurs naturally without a known cause.
2. Induced mutation- Resulting from the exposure of
organisms to mutagenic agents like ionizing radiation, uv light and
various chemicals.

31. BASED ON THE TISSUE OF ORIGIN-
1. SOMATIC MUTATION-
 Occurs in the somatic cells.
 In asexually reproducing species , somatic mutations transmits from one progeny
to next progeny.
2. GERMINAL MUTATIONS-
 Occurs in the gametic cells .
 Transmitted from one generation to the next gnenration.
BASED ON THE DIRECTION-
1.FORWARD MUTATION
 Occurs from the normal type to mutant allele.

32. 2.REVERSE MUTATION-
Occur from the mutant allele to a normal type.
CHROMOSOMAL MUTATIONS-
 Changes occur in the number and structure of chromsome.
 These include-
 1. CHROMOSOMAL ABERRATIONS-
 MORPHOLOGICAL CAHNGES IN THE CHROMOSOME WITHOUT
AFFECTING THEIR NUMBER.
 It is of 4 types-
 1. DELETION- Loss of gene block from the chrosome. It may be
terminal or intercalary.
 2. DUPLICATION- Presence of some genes more than once. It may be
tandem or reverse.

33. C. Translocation- transfer of gene block from one chromosome
to other.
D. Inversion- rotation of intercalary gene block through 180
degrees.

34. 2. Numerical chromosomal changes-
a. Eulpoidy – gain or loss of one or more genome. It may be-
Haploidy or polyploidy
b. Aneuploidy- gain or loss of one or two chromosomes. It may
be hypoploidy and hyperploidy.

35. GENE MUTATIOINS
 Invisible changes in the chemical nature of the gene.
 Many times a gene mutation does not produce any detectable
phenotypic effect as most of the gene mutations are recessive. But
the dominant gene mutations in homozygous condition may produce a
phenotypic change.
 The gene mutations are of three types:
 1. Frame shift mutations.
 2. Substitutions mutations.
 3. Point Mutations.

36. 1. Frame Shift mutations:
Mutations in which the reading of the frame of base
sequences shifts laterally either in the forward direction due
to insertion and in backward direction due to deletion
 So these are of two types-
 1. INSERTION- One or more nucleotides are added in the
segment of DNA representing cistron or gene.
 2. DELETION- one or more nucleotides are lost from the
segment of DNA representing a cistron or gene.

37. 2. SUBSTITUTION MUTATION-
 In a substitution, a nitrogen base is changed with another
 E.g.- In Sickle cell anemia , glutamic acid of B-chain of Hb-a is replaced by valine
amino acid to form defective Hb-s.
 These are of two types-
 1. Transition- purine is replaced by purine and a pyrimidine is replaced by a
pyrimidine.
 2. Transversion- Purine is replaced by pyrimidine or vice-versa.
-

38. 3. POINT MUTATIONS-
 A point mutation is a change in single nucleotide.
 It is of two types-
1. SYNONYMOUS MUTATION-
 Replaces a codon with another codon that codes for the same amino
acid .So the produced amino acid sequence is not modified.
 2. NON-SYNONYMOUS MUTATION-
 Replaces a codon with another codon that codes for a different amino
acid, so their amino acid sequence is altered.
 These are of two types-

39. 1. MISSENSE MUTATION-
These changes a nucleotide to cause substitution of different amino
acid . Thus in turn can render the resulting protein nonfunctional.
2. NON-SENSE MUTATION-
 Point mutation that Results in a premature stop codon, or a non-sense codon
In the transcribed mRNA and possibly a truncated and often nonfunctional
protein product.