Category: 12th Zoology

Genetic Engineering

Genetic Engineering (Recombinant DNA Technology)

All living organisms are endowed with specific genetic
information. With advancement that progressed in genetical science, many aspects of gene functions became obvious. The molecular functioning of genes revealed the central dogma that DNA in a eukaryotic cell undergoes transcription to synthesize RNA and the latter undergoes translation to
produce protein (polypeptide).

Even before the modern aspects of molecular genetics are discovered, the existence of mobile genetic elements (Transposons) were visualized by the geneticist Barbara Meclintock in her work on maize plant Zea mays in 1965.

Genetic engineering deals with the manipulation of genes
according to human will. A gene of known function can be transferred from
its normal location into an entirely different cell or organism, via a suitable
carrier or vector.

The carrier may be a plasmid DNA segment of a bacterium or a virus. The gene transferred likewise starts functioning to synthesize the particular protein in the new environment. Thus, the fact that, a gene can function irrespective of its environment formed the basis for genetic engineering.

Karyotyping of Human chromosomes

Post author By Mr. Padeepz
Post date November 2, 2018
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Karyotyping of Human chromosomes

The 23 pairs of chromosomes in human are classified into seven
groups viz, A-G based on position of centromere.

Group A : This group includes the largest chromosomes 1,2 and 3. These
are metacentric with centromere found in center with two equal arms.

Group B : This group represents chromosomes 4 and 5 which are
submetacentric with two unequal arms. (Karyotyping of Human chromosomes)

Group C : This is the largest group containing chromosomes 6,7,8,9,10,11,12
and X. These are of medium size and submetacentric. The X chromosome
resembles the chromosome 6 in this group.

GroupD : These are medium sized chromosomes with nearly
(acrocentric) terminal centromeres. The chromosomes 13,14 and 15 are kept
in this group.

Group E : It consists of chromosomes 16,17 and 18. They are shorter and
meta or submetacentric.

Group F : Shorter metacentric chromosomes 19 and 20 represent this group.

Group G : This group comprises the very short acrocentric chromosomes
21, 22 and Y belong to this category. (Karyotyping of Human chromosomes)

Uses : (Karyotyping of Human chromosomes)

1. Karyotyping helps to identify the sex of individuals through amniocentesis.
2. Genetic diseases in human beings can be detected by this
technique. If a disease is detected, the medical councelling for termination of
pregnancy and abortion of such foetus can be done.
3. By characterizing the normal karyotype, the chromosomal
abnormalities such as deletion, duplication, translocation, non-disjunctions
and the consequent aneuploids could be detected. (Karyotyping of Human chromosomes)

Human Genetics – Karyotyping

Post author By Mr. Padeepz
Post date November 2, 2018
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Human Genetics – Karyotyping

Karyotyping is a technique through which the complete set of
chromosomes are separated from a cell and the chromosomes are lined up in
a karyogram. The term karyogram has now been replaced by another word
called Idiogram referring to a diagrammatic representation of chromosomes.

The karyological studies are usually made during mitosis, though the
chromosome structure and details can also be best done in meiotic
preparations. It is much easier to obtain and prepare suitable mitotic cells.

Mitosis also reveals the replicated chromosomes viz., sister chromatids. The diploid set of chromosomes in the eukaryotic cells has
constant morphological (phenotypic) features such as number, size, shape.

The chromosomes are identified by other features such as the
secondary constriction, arm ratio, and banding pattern. The summation of all
such characters, which identify a set of chromosomes is called
karyotyping.

Karyotyping involves the culture of foetal cells found in the
amniotic fluid, in vitro, in a highly nutritive solution containing phytohaemagglutinin.

The foetal cells are cultured with colchicine. Colchicine stops
mitosis at metaphase. When these cells are subjected to a hypotonic
solution, the cells swell because the soluble salts are of lower concentration
than in normal protoplasm. The water diffuses into the cell and separates the
chromosomes.

The scattered chromosomes are then placed on a slide, stained
and photographed under a microscope. Individual chromosomes are then
cut off from the photograph and marked as homologous pairs to form an
idiogram.

MODERN GENETICS

Introduction and Scope

Genetics deals with various concepts and phenomena related to
inheritance. Mendel’s findings sowed the seeds for understanding the
secrets of heredity and paved the way for further knowledge on genes and
chromosomes. The post Mendelian period was remarkable in that many new
concepts and hypotheses related to general genetics such as factor (gene)
interactions, sex determination, linkage, sex linkage, crossing over, cytoplasmic
inheritance, multiple allelism polygenic inheritance were added.

The discovery of double helical DNA by Watson and Crick in 1953 has
unraveled the secrets of gene functions. The voluminous works on
Drosophila and prokaryotes like Escherichia coli opened up a new era of
modern (molecular) genetics. In modern genetics, human genetics
constitutes a part. It attempts to bring informations most important for
understanding the genetics of man who is also a species like any other
taxonomic species. Human genetics involves the identification of human
chromosomes; genetic engineering prospects; genetic diseases and gene
therapy; cloning devices; transgenic or genetically modified organisms etc.
Towards this line, the modern genetics also deals with the human genome
project; bioinformatics / biological data base and proteomics. (MODERN GENETICS)

Immune system disorders

The immune system is a multicomponent interactive system. It
effectively protects the host from various infections. But an improper
functioning of the immune system can cause discomfort, disease or even death.
The improper functions fall into the following major groups :
(1) hypersensitivity or allergy, (2) auto-immune diseases, and
(3) immunodeficiency. (Immune system disorders)

Hypersensitivity

Allergies result from an inappropriate and excessive immune response
to common antigens. Substances that cause allergies are called allergens ;
they include dust, moulds, pollen, certain foods, and some medicines (such
as penicillin). Allergy involves mainly IgE antibodies and histamine. Mast cells
secrete the histamine. A common manifestation of allergy is asthma. Sometimes
an allergen may cause a sudden, violent and fatal reaction in a sensititive
individual ; this is called anaphylaxis. (Immune system disorders)

Autoimmune diseases

Autoimmune diseases result when the immune system attacks and
destroys “self” cells and molecules. This condition can cause chronic and
serious diseases. Examples of autoimmune diseases are insulin-dependent
diabetes, multiple sclerosis, rheumatoid arthritis, etc. Multiple sclerosis is
caused by antibodies that attack the myelin sheath of nerve cells. (Immune system disorders)

Immunodeficiency diseases

Immunodeficiency Diseases result from a defect in one or more
components of the innate or adaptive immunity. Affected individuals are
susceptible to diseases that normally would not bother most people.
Immunodeficiency may result from gene mutations, infections, malnutrition
or accidents. (Immune system disorders)

a. Severe combined immunodeficiency (SCID) results from one of many
genetic defects; one such genetic defect leads to adenosine deaminase
deficiency. SCID is characterized by a very low number of
circulating thymocytes. Affected individuals usually die at an early age.

b. AIDS (Acquired Immuno Deficiency Syndrome) is another example for
immunodeficiency disease. It is caused by a retrovirus, known as human
immunodeficiency virus (HIV). Retroviruses have RNA genomes that are
replicated via DNA copies. HIV, selectively infects and kills T-helper cells.
The depletion of T-helper cells weakens the acquired immune response and
may even abolish it completely. The viral RNA genome is converted into
DNA copy by the viral enzyme reverse transcriptase. The DNA copy of
HIV becomes inserted into the human chromosome and replicates with the
cell DNA. It may be transcribed to produce RNA copies of the viral genome.
The RNA copies are packaged and liberated as virus particles. The infected
cell is lysed in this process, and the released virus particles infect new Thelper
cells. (Immune system disorders)

Unit 3 – Immunology Topic List Zoology

12th Zoology

Genetic basis of organ transplants

Post author By Mr. Padeepz
Post date November 1, 2018
No Comments on Genetic basis of organ transplants

Genetic basis of organ transplants :

Success of organ transplants (ie., Cornea, Kidney, Heart, Liver, Bone
marrow) and skin grafts depends on a proper matching of histocompatibility
antigens that occur in all cells of the body. Chromosome 6 of mouse contains
a cluster of genes known as the major histocompatibility complex (MHC),
which in humans is called human leukocyte antigen (HLA) complex. The
alleles of HLA genes determine the histocompatibility ie., the compatability
between donor and recipient tissues in transplants. (Genetic basis of organ transplants)

Process of graft rejection : (Allograft)

When the graft or tissue involves two genetically distinct members of
the same species, graft rejection occurs because the antigens of the graft and
host being different, the immune response of the host rejects the graft. The
graft dies, decays and is eliminated from the host. The host also reacts to the
graft and shows the following symptoms. 1.Skin rashes, 2. Fluid accumulation
in spleen and enlargement (Splenomegaly), 3. Emaciation (becoming
thin), 4. Diarrhoea, 5. hepatomegaly, 6. Anaemia and general immune suppression, 7. Damage in bile ducts, 8. Increased bilirubin synthesis etc. (Genetic basis of organ transplants)

Both cell mediated and humoral immune responses follow in rejection.
Sensitized T cells (lymphocytes), macrophages, plasma cells are all involved
in the primary or first set rejection. In the secondary or second set reaction,
B cells (B lymphocytes) and their antibodies are involved. In the cell
mediated reaction substances such as interleukin 1 (IL-1), Interleukin – 2
(IL-2) etc take part. The final lysis of the graft is achieved by lymphotoxins
or TNF (Tumour necrosis factors) or proteolytic enzymes.

In clinical fields, graft rejection is prevented by : 1.Blood groups
estimation (ABO and Rh) in the host, 2. Testing the presence of cytotoxic
antibodies in the host serum, 3. Cross matching of tissues (Host Vs graft)
prior to transplantation, 4. Giving immunosuppressive drugs like cyclosporin
and steroids etc to the host, 5. Total lymphoid tissue irradiation etc.
In recent years, the cloning technology promises to bring solution to
the problems of graft or tissue rejection in transplantation surgery. By stem
cell technology and cloning of cells, organ culture is feasible. Organs
cultured from the same embryo or individual are safe and valuable for
transplantation surgery. (Genetic basis of organ transplants)

Unit 3 – Immunology Topic List Zoology

12th Zoology

Transplantation immunology

Post author By Mr. Padeepz
Post date November 1, 2018
No Comments on Transplantation immunology

Transplantation immunology

The replacement of a diseased organ by a transplant (healthy tissue
or organ) is called transplantation. In the early 1940 Medawar explained
the nature of graft (transplant) rejection while working with the burn patients
of World War II. In his observations the following features were made clear.

1. graft of skin from one region of the body to another in the same patient
was easily accepted, 2. grafts obtained from close relatives like brother or
sister, were rejected 3. when a second graft was performed, by obtaining the
tissue from the same donor, the rejection reaction occurred with greater
intensity and speed. The graft or transplant leads to various complications in
the host body. (Transplantation immunology)

They are mediated by the host’s immune response. Very often the transplant gets rejected or may lead to graft verses host reaction or disease. Before discussing the nature and implications of this rejection phenomenon let us look into the terms involved in various types of grafts.

Classification of grafts : (Transplantation immunology)

The graft can be classified into four major types.

1. Autograft : The tissue of the original donor is grafted back into the same
donor. For example, skin graft from thigh to face in severely deformed case
of burnt individuals (plastic surgery).

2. Isograft : Graft between syngeneic individuals (ie., identical genetic
constitutuion). For example, clones or identical twins.

3. Allograft : (Homograft). Graft between allogenic individuals (ie.,
members of the same species but of different genetic constitution. For
example, kidney transplanted from one human to another.

4. Xenograft : (Heterograft). Graft between xenogenic individuals (ie.,
different genetic lineage). For example organ transplanted from pig to
human, baboon to human.

Unit 3 – Immunology Topic List Zoology

12th Zoology

Antibodies – Immunoglobulins

Post author By Mr. Padeepz
Post date November 1, 2018
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Antibodies Immunoglobulins

Immunoglobulins (Igs) are glycoproteins. Each molecule of Ig
consists of two pairs of polypeptide chains of different sizes. The smaller
chains are called ‘light’ (L) chains and the larger ones are called ‘heavy’
(H) chains.

The L chain has a molecular weight of approximately 25,000 and
the H chains is of 50,000. The L chain is attached to the H chain by a
disulphide bond. The two H chains are also joined together by
S-S bonds, depending on the class of immunoglobulins. The H chains are
structurally and antigenically distinct for each class and are designated by the
Greek letter corresponding to the immunoglobulin class, as follows :
IgG (Gamma) IgA (alpha ) IgM(mu) Igd (delta) and IgE (epsilon)

The L chains are similar in all classes of immunoglobulins. They
occur in two varieties, kappa (k) and lambda (l). A molecule of
immunoglobulin may have either kappa or lambda chains, but never both.

Region of polypeptide chains

Each heavy and light chains consists of two regions viz.,

1.The variable (V) region or Fab region: The V region shows a wide
variation in amino acid sequences in the amino or N-terminal portion of the
molecule. These areas of high variability in the variable region of H and L
chains are called ‘hotspots’ or hypervariable regions. These hotspots are
most intimately involved in the information of the antigen-binding site. In
both VH and VL regions of the chain atleast three hypervariable regions/
hotspots are present. The infinite range of the antibody specificity of
immunoglobins depends on the variability of the amino acid sequences at the
‘variable regions’ of the H and L chains, which form the antigen combining
sites (Paratope). Immunoglobulins

2. Constant (c) region (or) Fc region (Fc = fragment of constant region) :
The C region denotes constant region with unvarying amino acid sequence in
the C or COOH terminal portion of the molecule.
(Fab – Fragment of antigen binding site
Fc – Fragment of constant region)
Depending on the observable reaction produced on mixing with antigens,
the antibodies are designated variously as agglutinins,
precipitins and so on. Sera having high antibody levels following infection
or immunization are called immune sera or anti sera. Immunoglobulins

Unit 3 – Immunology Topic List Zoology

12th Zoology

Antigenic determinants and epitopes

Post author By Mr. Padeepz
Post date November 1, 2018
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Antigenic determinants and epitopes

The part of the antibody molecule which makes contact with the
antigen is termed the paratope. Consequently, the part of the antigen
molecule that makes contact with the paratope is called the epitope. As
most antigens are protein in nature, they exist in a folder, three dimensional,
tertiary structure. Hence there may be a cluster of amino acid sequences on
the three dimensional structure constituting a series of epitopes. Each of these
epitope clusters on the antigen are known as an antigenic determinant.

Generally the substances, which are capable of eliciting an immune
response, that is, the synthesis of antibodies are called antigens. However
the above definition of antigens do not infer the cell mediated response. Hence
the term immunogen is introduced to denote antigenic substances which elicit
both humoral and cell mediated immune response or either humoral or cell
mediated response. (Antigenic determinants and epitopes)

Antigens may be either natural or artificial/synthetic ones. Natural
antigens, fall into two categories viz., particulate antigens and soluble
antigens. Bacteria, viruses, erythrocytes and cells represent particulate type
antigens. Bacterial toxins, proteins, carbohydrates, glycoproteins and
lipoproteins represent the soluble antigens.

In addition, a variety of chemical compounds, biological
macromolecules, synthetic polypeptides are regarded as potential antigens.
Several polysaccharides, nucleoproteins and lipoproteins are also considered
as antigens. Recently antibodies to DNA have been used in immunization. (Antigenic determinants and epitopes)

Unit 3 – Immunology Topic List Zoology

12th Zoology

Secondary Lymphoid Organs

Post author By Mr. Padeepz
Post date October 30, 2018
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Secondary Lymphoid Organs

Mucosa associated lymphoid tissues (MALT) :

The mucosa lining the alimentary, respiratory, genitourinary and other
lumina and surfaces are constantly exposed to numerous antigens. These
areas are endowed with a rich collection of lymphoid cells, either specialized
aggregates as the Peyer’s patches or Scattered isolated lymphoid follicles
– collectively called the Mucosa associated lymphoid tissues (MALT).

Such lymphoid tissues in the gut are called Gut associated lymphoid tissue
(GALT) and those in the respiratory tract are called Bronchus associated
lymphoid tissue (BALT). MALT contains lymphoid cells as well as
phagocytic cells. Both B and T cells are present. The mucosa is endowed
with secretory IgA. The mucosal regions afford/confer protection from many
enteric and respiratory infections. (Secondary Lymphoid Organs)

Antigens

The terms immunogen and antigen are often used synonymously.
However, these terms imply two closely related entities. The first describes a
molecule that provokes an immune response(immunogenicity) and hence is
called an immunogen. The other describes a molecule which reacts with the
antibody produced, or with the activated cellular constituents of cell
mediated immunity(antigenicity), and is referred to as an antigen. (Secondary Lymphoid Organs)

In contrast to this is the hapten. Haptens are small well defined
chemical groups such as dinitrophenol (DNP) which are not immunogenic on
their own but will react with preformed antibodies. To make a hapten immunogenic, it must be linked to a carrier molecule which is itself immunogenic.
Antigens are recognized not only by antibodies, but also by antigen
specific T cell receptors. In contrast to immunoglobulins, which usually
recognize intact antigens, T cell surface receptors recognize processed
antigens on the surface of antigen presenting cells. (Secondary Lymphoid Organs)

UNIT 5. ENVIRONMENTAL SCIENCE Topic List Zoology

UNIT 5. ENVIRONMENTAL SCIENCE Topic List Zoology

UNIT 5. ENVIRONMENTAL SCIENCE Topic List Zoology

UNIT 5. ENVIRONMENTAL SCIENCE Topic List Zoology

Genetic Engineering (Recombinant DNA Technology)

Related Topics in Zoology:

UNIT 5. ENVIRONMENTAL SCIENCE Topic List Zoology

Karyotyping of Human chromosomes

Uses : (Karyotyping of Human chromosomes)

Related Topics in Zoology:

UNIT 5. ENVIRONMENTAL SCIENCE Topic List Zoology

Human Genetics – Karyotyping

Related Topics in Zoology:

UNIT 5. ENVIRONMENTAL SCIENCE Topic List Zoology

MODERN GENETICS

Introduction and Scope

Related Topics in Zoology:

UNIT 5. ENVIRONMENTAL SCIENCE Topic List Zoology

Immune system disorders

Hypersensitivity

Autoimmune diseases

Immunodeficiency diseases

Related Topics in Zoology:

Unit 3 – Immunology Topic List Zoology

Genetic basis of organ transplants :

Process of graft rejection : (Allograft)

Related Topics in Zoology:

Unit 3 – Immunology Topic List Zoology

Transplantation immunology

Classification of grafts : (Transplantation immunology)

Related Topics in Zoology:

Unit 3 – Immunology Topic List Zoology

Antibodies Immunoglobulins

Region of polypeptide chains

Related Topics in Zoology:

Unit 3 – Immunology Topic List Zoology

Antigenic determinants and epitopes

Related Topics in Zoology:

Unit 3 – Immunology Topic List Zoology

Secondary Lymphoid Organs

Mucosa associated lymphoid tissues (MALT) :

Antigens

Related Topics in Zoology:

Unit 3 – Immunology Topic List Zoology