Notes
Genetics
Genetics is the branch of biology that deals with study of heredity and
variations. The term was given by Bateson in 1906.
Mendel
Gregor Johann Mendel is known as Father of genetics as he discovered the
mechanism of transmission of characters from one generation to the next. He
chose Garden Pea (Pisum sativum) as
his experimental material.
Monohybrid cross
It is a cross between two organisms of the same species which studies the
inheritance of two factors of traits of a single character. e.g. tall and dwarf
Pea plant.
Dihybrid Cross
It is a cross between two organisms of same species which is made to
study inheritance of two pairs of factors or traits of two characters.
Variation:
Variations are
differences present in morphological, physiological and other traits found
among individuals belonging to the same family, race and species.
Significance of variation:
1. It is the source of
raw material for evolution.
2. Animals are able to adapt themselves to the changing environment.
3. Organisms are better suited to face the struggle for existence.
4. Variations give the organisms an individuality of their own.
5. Without variation, there would be no science of heredity as all individuals of a race, would be identical in all aspects
2. Animals are able to adapt themselves to the changing environment.
3. Organisms are better suited to face the struggle for existence.
4. Variations give the organisms an individuality of their own.
5. Without variation, there would be no science of heredity as all individuals of a race, would be identical in all aspects
Speciation
Mutation
Organisms have evolved
in number of ways to protect their DNA from changes. In spite of these
mechanisms, however, changes in the DNA occasionally do occur. Any change in
the DNA sequence is called a mutation. Mutations can be caused by errors in
replication, transcription, cell division, or by external agents. E.g. nuclear
radiation can lead to mutation
……..
Evolution
Evolution may be defined as a gradual development of more complex species from pre-existing simpler forms.
It is an extremely slow process and has occurred over millions of years,as revealed by fossil evidences.
Evolution has thus resulted in the diversity of organisms, influenced by environmental selection
Evolution may be defined as a gradual development of more complex species from pre-existing simpler forms.
It is an extremely slow process and has occurred over millions of years,as revealed by fossil evidences.
Evolution has thus resulted in the diversity of organisms, influenced by environmental selection
Darwin
Charles Robert Darwin
(1809-1882), a naturalist, worked on the theory of evolution. He gave Theory of
Natural Selection which is also known as Darwinism. The theory states that
organic evolution occurs through natural selection and accumulation of
inheritable variations which provide structural and functional superiority to
some individuals over others in their survival and reproduction.
Natural Selection
Natural
selection is the process by which species adapt to their environment. Natural
selection leads to evolutionary change when individuals with certain
characteristics have a greater survival or reproductive rate than other
individuals in a population and pass on these inheritable genetic
characteristics to their offspring.
Genetic Drift
Genetic
drift refers to the change in a type of genes in a population due to a random
occurrence. In other words, a random circumstance causes a certain genetic
trait to become more common or rarer over time.
Traits
A trait
is a distinct variant of a phenotypic character of an organism that may be
inherited, environmentally determined or somewhere in between.
For example, eye color is a character
or abstraction of an attribute, while blue, brown and hazels are traits.
Acquired traits
An acquired
trait is defined as a characteristic or trait that produces a phenotype
that is a result of an environmental influence. Acquired traits are not coded
for in the DNA of an individual and therefore cannot be passed down to
offspring during reproduction. In order for a characteristic or trait to be
passed down to the next generation, it must be part of the individual's genotype
Inherited traits
A trait or character
that is genetically inherited or passed down from generation to generation
Origin of Life on Earth (Chemical Evolution of Life)
Speciation
Speciation
is arising of a new species from a sub-population of a species which is
geographically or reproductively isolated over a long period of time from the
other population of the same species.
Evolution and Classification
Tracing Evolutionary Relationships
Homologous Organs
Analogous Organs
Vestigial Organs
Fossils
A fossil is evidence
of an organism that lived long ago. These are remnants or impressions of the
extinct organisms which existed on earth millions of years ago.
Fossilisation
Fossils can be of
following types:
- Trace Fossils: These are indirect evidence of the dead organism. E.g. footprint, trail etc.
- Casts: In rocks, the spaces are filled with dead organism making ts its replica or cast.
- Molds: organism buried in sediment and decayed leaving an impression.
- Petrified Fossils: minerals replacing the hard part of the organism
- Frozen Fossils: Organism trapped in ice or in tree sap which hardened later.
Fossils help us
understand the process of evolution in following ways:
- These are the clues to the past, thus trace the path of evolution.
- Help in building evolutionary
relationships among the present organisms. E.g. fossil evidence like Archaeopteryx
and some characteristics of present-day birds like this hoatzin suggest
that dinosaurs might have been the ancestors of today’s birds. - Fossils help us in learning diversity of life and animal behaviour in past. This helped in understanding ancient environment and climate and categorizing geological time scale.
