GENETICS and EVOLUTION

GENETICS:

THE branch of biology that deals with the transmission and variation of inherited characteristics in particular chromosome and DNA.

EVOLUTION:

Gradual directional change especially one leading to a more advanced or complex form ;growth development.

Development Of Genetics

The genetics is new science it developing early part of the twentieth century.

Twentieth century the British geneticist Bateson and R.C. Punnett was giving such a public lecture before an audience in London explained human genetics.

Instead of using flower or cotyledon color as example of early mendalism.

MENDEL

Dr. R.C.Punnett used as the inheritance of human eye color.

Brown eye Blue eye BB bb

Bb F1generation(brown eyes)

B b B F2 generation b

BB

Bb

Bb

bb

The F2 generation phenotype ratio=3:1 genotype ratio=1:2:1 It is know that this example of inheritance of eye color in man is not 100% correct. But it is a reasonably good approximation to a simple mendalian monohybrid cross.

HARDY-WEINBERG LAW

This principle says that allele frequencies in a population are stable and is constant from one generation to next generation. Finally assume that there is no migration, no selection and no mutation.

Hardy law formula worked out 1908 and also independently by the German physician Weinberg.so the law become known as Hardy-Weinberg law or Hardy-Weinberg equilibrium.

Hardy Weinberg

The formula of hardy-Weinberg law

Brown eye Blue eye BB bb

Bb F1generation(brown eyes)

B b B F2 generation b

BB Bb

Bb bb

Simple algebra 2 initial frequency of BB=P 2 initial frequency of bb=q

only two alleles involved so, P+q=1(F1 generation)

the distribution genotype in next generation

the genotype of F2 generation=1:2:1 2 2formula is p+2pq+q=1

sum total of all the allelic frequency is 1.in case evolution doesn’t occur. Change of frequency of alleles in a population would then be interrupted as resulting in evolution.

There are 2 aspects of Hardy-Weinberg law

1.The relative frequencies of the 2 alleles remain constant from one generation to next.2.The 3 genotypes occur in quadratic proportion in population that are at equilibrium.

2 23 possibilities of genotype p 2pq q

Factors are affect the HARDY-WEINBERG equilibrium

1. Migration or Gene flow2. Genetic drift 3. Mutation4. Recombination5. Natural selection

Process Of Evolution

The evolution implies change with respect to time. The genetics is a major factor in evolution Hardy-Weinberg formula state that the population remain

constant

The 4 process in evolution1. Mutation 2. Recombination 3. Natural selection4. isolation

Mutation The 1ST Important factor of evolution is mutation. Mutation is the only mechanism that can introduce genetic

variability. Mutation provides the raw material for evolution Mutation :it supplies the genetic variation to population that

makes possible the new genotypes, that may be necessary for the evolution success of the population.

ie: mutation are sudden heritable changes in the genetic make up of an organism. Mutation are stable. Mutation lead to evolution In 2 ways 1---ADAPTATION 2---ADAPTABILITY

ADAPTATION

The oversimplification, assume that there is one particular genotype that best adapts the population to a particular environmental niche(the sum total of all the environmental impacts on the organism).

If this assumption is true it can be shown that the population will tend toward homozygosity for that single genotype that best adapts it to the ecological situation.

The tendency for a population to become homozygous can be spoken of as adaptation.

TALL AA

DWARF aa

A aAa

P

GF1

Aa Aa

AA Aa

Aa aa

A aA

a

F2

ADAPTABILITY

The adaptation serve the well-being of the species only as long as the environment stays constant.

In geological record of the earth knows that the environment doesn't remain constant.

In most areas the earth organisms are subjected to daily life cycles of environmental change involving heat ,light and seasonal cycles.

That the population that tends toward homozygosity is also likely to become extinct.

The tendency of a population to become heterozygous is defined as adaptability

TALL AA

DWARF aa

A aAa

P

GF1

Aa Aa

AA Aa

Aa aa

A aA

a

F2

Genetic variation

During the long evolutionary period most possible mutations have occurred at one time or another and have been selected against or rejected as not being the highly adapted.

Mutation is the only mechanism that can introduce genetic variability

Gene mutation

The particular mutation involves a change of the chemical quality of the gene.

In recent year: several chemicals have been found that cause marked increase of the rate at which mutations occur this is called as mutagenic substances.

Eg; 5-Bromo-uracil it almost identical with thymine.

Recombination

Recombination is 2nd factor considered important for evolution.

It defined as the formation of genetic combinations in offspring that are not present in the parent.

Mutation is the ultimate source of variability. Mutation build up a large storehouse of variation.

Recombination of this genetic variation provides the many possible genotypes that might mean the difference between survival and extinction for a given population.

The significance of recombinationNo: of heterozygous

gene pair 1 2 3 23

n

No :of different kinds of gamete produced

2 4 8 8,388,608

n 2

Importance of crossing over:

No: of possible genotypes were determined no: of chromosome involved.

The no: of genes in most organisms is relatively large the possible no: of genotypes from recombination due to crossing over become almost infinities.

Recombination of all the variation that has accumulated with time provides that favorable genotype that now allows the population to survive in the new environment.

In human 99% gene are homozygous and 1% total genotype varying from individual to individual.

Natural selection

Natural selection is the 3rd factor of evolution. When Darwin wrote his monumental book on the

origin of species in1859,the title also contained the words by natural selection.

Natural selection is defined as :some organism are better adapted to survive in an otherwise hostile environment. Adaptive ability is inherited. The end result of the ability to adapt and get selected by nature.

DARWIN

it is an example of natural selection

Eg:iguana

Terrestrial habit, carnivores

Iguana (marine habit)

Industrial melanism

A classical example of natural selection involves pigmentation in the Lepidoptera, Moths and Butterflies.

In this nineteenth century it has been possible to test genetically the dark forms and the light forms with respect to their adaptive values. The experiments indicate that, under laboratory conditions, the melanic form is superior in viability to the light form.

As a result of the change in environmental background, the melanic forms greatly increased in frequency in the population.

Natural selection the genetic constitution of a population has changed with time.

Adaptive value: The population is composed of many organisms. Assume for simplicity, that each organisms has a different genotype, further assume that one of these genotypes is better than any of the other, that it has highest adaptive value .

Adaptive polymorphism: Populations that show two or more variants are called polymorphic. Phenotypically the population is same but in genotypically different. Polymorphism within a species increases adaptability, there by providing for the genetic change.

Eg: human blood group A,B,AB and O

Isolation

Isolation is the 4th factor in evolution. Isolation is defined as the separation of two or more

population to prevent the interbreeding. After the twentieth-century arises more principle that

essentially supported by the Darwinism. The geneticists interested in evolution are often

referred to as an Neo-Darwinians (Dobzhansky).

Neo- Darwinism or modern synthetic theory

Neo Darwinism=Darwin concept of natural selection+gregor mendal basic+population geneticist+molecular biology.

Modern synthetic theory of evolution recognize 5 basic types of process.1.Recombination 2.Mutation3.Gene flow 4.Natural selection 5.Gene frequency changes Genetic drift

Hardy Weinberg

DOBZHANSKY

Isolating mechanisms(Dobzhansky)

Isolating mechanisms that tend to separate the two populations and prevent interbreeding.

Buildup of isolating mechanisms takes a very long time.

The isolating mechanisms into two major groups.

1.Geographical isolation 2.Reproductive isolation

Premating

post mating

Geographic isolation: In which the interbreeding and gene exchange between population are limited or prevented because the two populations occupy separate geographical areas and do not come contact with each other. There is no gene exchange.

Reproductive isolation: The populations are not necessarily physically separated but are prevented from exchanging genes through one or more different isolating mechanisms. it 2 types 1.premating or prezygotic mechanisms prevent the formation of hybrid zygote 2.postmating or zygotic isolating mechanisms reduce viability or fertility of hybrid zygotes

Premating or prezygotic mechanisms prevent the formation of hybrid

zygote1.Ecological or habitat isolation ===The population concerned occur in different habitats in the same general region.2.Seasonal or temporal isolation===Mating or flowering times occur at different times3.Sexual or ethological isolation===Mutual attraction between the sexes of different species is weak or absent

Post-mating or zygotic isolating mechanisms reduce the viability or fertility

of hybrid zygotes1.Hybrid inviability===Hybrid zygotes have reduced viability or inviable

2.Hybrid sterility ===The F1 hybrids of one sex or both sexes fail to produce functional gametes.3.Hybrid breakdown====The F2 or back cross hybrids have reduced viability or fertility

Population

Population is defined as a collection of organisms of a particular species, sharing a particular characteristics of interest, most often that of living in given areas.

Population is two types 1.Allopteric===Populations that are separate from each other. 2.sympateric==evolution where speciation occurs when two populations are found in the same areas