1. (T.Y.B.Sc. BOTANY PAPER –III BO.333: GENETICS AND EVOLUTION GSD )
Sir Parashurambhaucollege, Pune-30
Department of Botany
Chapter. 1. INTRODUCTIONOF GENETICS
Dr. Dhulgande G. S.
Asst. prof.
2. Introduction and Definition:
The word "genetics" is derived from the Greek word
"genesis" means "to grow" or "to become” or “to
express”.
“Genetics is the study of heredity and variations.”
The Science that deals with the mechanisms
responsible for inheritance of similarities and differences
in a species is called Genetics.
It is a branch of biology that encompasses the study
of the mechanism of transmission of characters from
parents to offspring’s.
3. Heredity and variations are controlled by genes-
what they are, what they do, and how they work.
The traits are described by the genetic information
carried by a molecule called DNA.
The instructions for constructing and operating of
an organism are contained in the organism's DNA.
Every living thing on earth has DNA in its cells.
A gene is a hereditary unit consisting of DNA that
occupies a spot on a chromosome and determines a
characteristic in an organism.
4. A gene is one particular section of a DNA molecule that tells a
cell to perform one specific task.
Genes are passed on from parent to child and are believed by
many to be an important part of what decides looks and behavior.
Darwin’s theory of Natural selection laid the groundwork for
evolutionary theory.
However, it was the emergence of the field of genetics,
pioneered by Gregor Mendel (1822-1884) that provided the missing
information on how evolution works in practice.
Mendel’s experiments with pea led him to realize that
heredity in sexual reproduction works by the mixing of separate
factors, not by the blending of inherited characters.
This combination of Darwin's theory and our current
understanding of heredity led to the birth of the scientific area called
"population genetics."
5. Concept of heredity and variations:
The children or offsprings closely resemble their parents
and to some extent their grandparents and great
grandparents.
The Science of Genetics helps us to differentiate between
heredity and variations and seeks to account for the
resemblances and differences due to heredity, their source
and development.
6. Heredity refers to the transmission of characters,
similarities as well as differences from one generation to
the next. It explains how offsprings in a family resemble
their parents.
Heredity literally means “tendency of like begets like” i.e.
all living organisms tend to produce offspring’s like
themselves.
Variation refers to the differences shown by individuals of
the same species and also by offsprings (siblings) of the
same parents.
It explains why offsprings even though born to the same
parents differ from each other. They are similar, but not
identical (except in identical twins).
These similarities and differences are not coincidental.
7. Types of Variation:
The variations may be classified into two types:
1) Hereditary variation:
The variations which arise as a result of any
change in the structure and function of the gene and are
inherited from one generation to another are called hereditary
variation.
2) Environmental Variations:
Two individuals with the same genotype may
become different in phenotype when they come in contact
with different conditions of food, temperature, light, humidity
and other external factors. Such differences among
organisms of similar heredity are known as environmental
variation. These are not heritable.
8. Based on the type of cells, variation is classified into
two types.
1) Somatic Variation:
The variation which occurs in somatic
cells is called somatic variation. It is generally
insignificant, because it is not inherited from
parents. It is acquired by the organisms during their
own lifetime and is lost with death. Hence, it is also
called acquired variation.
2) Germinal Variation:
The variation which occurs in the
germinal or reproductive cells is called germinal
variation. It is heritable and genetically significant. It
provides raw materials for evolution.
9. Based on the degree of differences, variation is classified into
two types:
1) Continuous Variation:
Small, indistinct and slow variations are
called continuous variation.
a) These are fluctuating with environmental conditions.
b) These are non-heritable.
c) They have no role in evolution.
d) They are most common and occur in all organisms.
2) Discontinuous Variation:
Large, distinct and sudden variations are
called discontinuous variation.
a) These are relatively unaffected by environmental
conditions.
b) These are heritable.
c) They provide raw materials for evolution on which
selection is based.
d) They are not common and appear suddenly.
10. Branches of Genetics:
Genetics is an interesting combination of Biology and
mathematics and gives you a deep insight into how things work in a cell,
how different phenotypes are observed in an organism and how dynamic
a population can be. There are some of the significant branches of
genetics are as follows:
1. Microbial genetics: It is a subject area within microbiology and genetic
engineering. It studies the genetics of very small (micro) organisms;
bacteria, archaea, viruses and some protozoa and fungi. This involves the
study of the genotype of microbial species and also the expression
system in the form of phenotypes.
2. Plant genetics: This branch concern with all genetical and hereditary
aspects of plants. It is very broad term.
3. Animal genetics: This branch concern with all genetical and hereditary
aspects of animals. It is also very broad term.
4. Human genetics: Human genetics can be defined as a field of science
that deals with the inheritance of traits that can be traced through
generations.
11. 5. Classical genetics: It is the branch of genetics based solely on visible
results of reproductive acts. It is the oldest discipline in the field of
genetics. Classical genetics consists of the techniques and
methodologies of genetics that were in use before the advent
of molecular biology.
6. Molecular genetics: It includes the study of detailed structure and
function of genes and regulation of its activity.
7. Cytogenetics: It can be defined as the study of chromosomes, the
hereditary units. It has been an active field of research contributing to the
understanding of organization of chromosomes and human genome. It is
a discipline that matches phenotypes to detectable chromosomal
abnormalities.
8. Population genetics: It is a subfield of genetics that deals with genetic
differences within and between populations, and is a part of evolutionary
biology. Studies in this branch of biology examine such phenomena
as adaptation, speciation, and population structure.
12. 9. Genetic engineering: Genetic engineering, also called genetic
modification or genetic manipulation, is the direct manipulation of an
organism's genes using biotechnology. It is a set of technologies used to
change the genetic makeup of cells, including the transfer of genes within
and across species boundaries to produce improved or novel organisms.
10. Biochemical genetics: By definition, the field of biochemical genetics
deals with the inheritance of genes that control the activity of an enzyme
that catalyze the specific biochemical reaction in a metabolic pathway.
11. Genomics: Genomics can be defined as the structural and functional
studies of genome that represents the total content of DNA within an
organism or cell, including nuclear and mitochondrial DNA.
12. Transgenics: It is concern with transfer of genes in plants as well as in
animals.
13. Pharmacogenomics: Pharmacogenetics is a growing field and is
defined as the discipline that deals with inheritance of drug sensitivity in
humans.
13. Applications of Genetics:
In the modern world genetics plays an important and crucial role in the field
of biological study. It has an impact in a wide variety of areas, from curing
diseases to growing better vegetables to catching criminals. Genetics has scope
in following fields:
• Improvement of plant production:
Genetics and genetic engineering has placed an important role in
improvement of plant production. There are following applications of genetics in
plant improvement.
•Production of polyploid crops:
The techniques of genetics for ‘producing polyploid’ crops have improved the
yield of crops. Today most of major crops like wheat, corn are polyploid. Green
revolution has dramatically,’ improved the production of grains. Thus it reduced
hunger and famine on the earth.
•Hybridization:
It is a traditional technique. The crossing of different varieties of plants
species is called hybridization. Hybridization is used to produce plants with
desirable traits.
•Transgenic plants:
The plants with foreign DNA are called transgenic plants. Many new are
introduced into different types of plants.
•Insect and herbicides resistant plants:
Cotton, corn, potato and soybean plants are engineered. These plants are
resistant to insect predation or herbicides.
14. 2. Synthesis of pharmaceutical products:
A foreign gene is replicated and expressed in these bacteria. Thus
a large amount of protein product is obtained. Many biotechnology
products are produced by bacteria. These products are now available in
markets. Some of these products are: Insulin, Human growth hormone,
Tissue plasminogen activator, Haemophilia factor VIII, Hepatitis B vaccine
3. Promoting health in plants:
Transgenic bacteria are used to promote health of plants. For
example: A bacterium normally forms colonies in the roots of corn plants.
Some genes from another bacterium have been inserted into these
bacteria. These genes code for an insect toxin. The toxin protects the
roots from insects.
4. Role of genetics in conservation of wild life:
Wild life has great ecological significance for human. Extinction
of many species is upsetting the ecological balance. Conservation of wild
life is impossible without genetic conservation. Genetic conservation
means conservation of variety of genes of the endangered species.
Genetic laws are being applied for the genetic conservation programmes.
15. 5. Biodegradation:
Bacteria can degrade a particular substance. The ability of
degradation of bacteria can be enhanced by genetic engineering.
6. Biofilters:
The transgenic bacteria can be used as biofilter in industries.
7. Synthesis of organic compounds:
The catalysts act on precursor molecules during synthesis- of
organic chemicals. Bacteria can be used in place of these catalysts.
These bacteria carry out the synthesis of these compounds. For example,
aspartame is dipeptide sweetener. It is known as Nutrasweet. It is
prepared by transgenic bacteria.
8. Use in Mining industry:
Many major mining companies are using bacteria to obtain
various metals. Genetic engineering enhances the ability of bacteria to
extract copper, uranium and gold from low grade sources.
16. 9. Gene therapy:
The insertion of genetic material into human cells for the treatment of
a disorder is called gene therapy. Gene therapy is used for two purposes:
There are two main methods used for gene therapy i.e. Ex-vivo and in
Vivo.
•Ex-vivo gene therapy: The gene therapy in which genes are inserted into
the cell outside the body is called Ex-vivo gene therapy. Following
diseases are treated by ex vivo gene therapy: SCID,
hypercholesterolemia, etc.
•In-vivo gene therapy: The gene therapy in which genes are inserted in the
cells within the body is called In-vivo gene therapy. Following diseases
are treated by these techniques: Cystic fibrosis, cancer Coronary artery
angioplasty hemophilia, diabetes Parkinson disease and AIDS, etc.
•DNA finger printing: DNA analysis can be used for following purposes:
1. Diagnosis: DNA analysis is used to diagnose viral infections, genetic
disorders, and cancer.
2. Use in forensic laboratories: DNA analysis is used to identify criminals.
10. Clinical genetics:
Physicians are trained as Geneticists diagnose. They treat, and
counsel patients with genetic disorders or syndromes.
