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 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.
2.What is meant by Idiogram?
The term karyogram has now been replaced by another word called Idiogram referring to a diagrammatic representation of chromosomes.
3.Why are mitotic cells important?
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.
4. How is Karyotyping done in human Chromosomes:
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 ideogram.
5.Describe the classification of 23 pairs of chromosomes in human?
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.
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.
6.What are the uses of Karyotyping?
1. Karyotyping helps to identify the sex of individuals through amniocentesis.
7.Explain briefly Genetic Engineering?
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.
8. List the tools required for genetic Engineering?
1.Enzymes:a. Exonucleases, b. endonucleases, c. restriction endonucleases, d. SI enzymes to convert the cohesive ends of single stranded DNA fragments into blunt ends, e. DNA ligases, f. Alkaline phosphatase, g.Reverse transcriptase, h. DNA polymerase etc.
2.Foreign DNA / Passenger DNA : It is a fragment of DNA molecule, which is to be enzymatically isolated and cloned.
3. Cloning vectors : Vectors or vehicle DNA are those DNA that can carry a foreign DNA fragment when inserted into it. The vectors generally used are bacterial plasmids and bacteriophages.
9.What are plasmids?
A plasmid is a circular DNA with about 200-300 nucleotides. It is present in bacterial cells alongside their main chromosomes. A plasmid sometimes can leave from one bacterial cell and enter another, through, conjugation and thereby transfer genetic traits to the recepient cell. The plasmid DNA inside a bacterium can replicate independently of the main DNA and can depart from main genome dragging a piece of main DNA along with it. It is called the bacterial DNA. A plasmid can sometimes fuse with the main DNA. Thus the plasmid seems to be an efficient gene exchanging vehicle which the nature has produced.
10.How is a gene isolated?
In recombinant DNA technology, restriction endonucleases cut the DNA double helix in very precise manner. They recognize specific base sequences on DNA. They cut each strand of DNA at a given place.
11. What is referred to as a palindrome with a suitable example?
The enzymes recognize specific DNA sequences which are called palindrome sequences. A palindrome refers to a base sequence that reads the same on the two strands but in opposite directions. For example if the base sequence on one strand in GAATTC read in 5'-3' direction, the sequence on the opposite (complementary) strand is CTTAAG read in 3 '-5' direction. There is a point of symmetry within the palindrome. In the example given this point is in the center between the AT/TA.
12.Give an example of restricition enxymes?
Escherechia coli (ECoRI)
The restriction enzymes cut the DNA molecule around the point of symmetry. The above palindrome sequence is recognized by the restriction enzyme derived from Escherechia coli, called EcoRl. It cuts the DNA molecule into discrete fragment with staggered cut ends.
13.What is recombinant DNA?
The foreign DNA fragment isolated is made to recombine with the plasmid DNA which is cleaved by the same restriction endonuclease. The recombination of the two DNAs is effected by the DNA ligase enzyme. The product formed is called recombinant plasmid or recombinant DNA.
14.Explain Molecular cloning:?
The recombinant DNA must be introduced into a host cell, within which it may replicate freely. Escherechia coli has been employed as a suitable host to the above. Alongside, with the multiplication and growth of the bacterium in the medium, copies of rDNA are also produced.
When the rDNA copies are introduced into the host cells, (E. coli) a few thousand of rDNA pieces may enter the cells. These cells are called transformed cells. Each transformed cell grows a colony of its own in which every member is genetically alike. These colonies are then distinguished and recultured separately.
From the recultured colonies, the recombinant DNA is extracted from lysed cells, purified and used.
15.Give three application and uses of DNA technology?
1. Genetic engineering/recombinant DNA technology has enabled the understanding of structure of eukaryotic genes and their components.
2. Genetically engineered bacteria are employed to synthesize certain vital life saving drugs, hormones and antibiotics eg., Antiviral / anticancer interferons ; human growth hormone (HGH) somatostatin, etc.
3. Through recombinant DNA technology, the genotypes of plants are altered. New transgenic plants which are resistant to diseases and pest attack have been produced.
16. What are called Superbugs?
Genetically engineered bacteria are called superbugs.
17.Which is the superbug used to clear up oil spills?
The super bug was produced first by an Indian researcher Anand Jhakrabarthy in USA. He developed a strain of Pseudomonas bacterium to clear up oil spills. The above superbug can destroy octanes, xylenes camphors and toluenes.
18.Explain DNA Segmenting.
DNA segmenting in genetic engineering refers to fragmenting of DNA and sequencing or mapping the DNA in terms of its nucleotide sequences. Chemical and enzymatic methods are available. As a result the gene and non-compartments of DNA can be identified.
19. What is Pedigree analysis?
The scrutiny of established matings to obtain information about the genetic characters / traits is called pedigree analysis.
20.Explain Pedigree Chart?
Pedigree chart defines the history of a character in a family. It is drawn up using certain standard symbols. It is also called as the Family tree. Pedigree chart helps to identify and visualize the course of genetic diseases in the progeny. This is especially true of diseases such as fibrosis and phenylketonuria (PKU).
21.Explain Sickle cell anaemia ?
Sickle cell anaemia is a genetic syndrome caused by an autrosomal mutant allele Hbs. In homozygous conditions (Hbs Hbs). It causes the production of an abnormal haemoglobin called haemoglobin S. The normal haemoglobin is designated as HbA (HbA HbA).Sickle cell persons with the genotype HbsHbs suffer from a fatal haemolytic anaemia. The patient dies due to damaged heart, kidney, spleen and brain as a result of clogged blood vessels or vascular obstructions. Persons with heterozygous genotype HbA HbS are said to be carriers and they survive.
22.Explain Thalassemia ?
Thalassemia is an erythroblastic anaemia due to homozygous recessive gene expression in children. Two types of this disease viz., thalassemia major and thalassemia minor exist. The homozygotes suffer from severe thalassemia while all heterozygotes suffer from milder thalassemia. The clinical manifestations of thalassemia include I) decrease in the bone marrow activity, ii) peripheral haemolysis, iii) splenomegaly (enlarged spleen) and hepatomegaly, (enlarged liver) etc. The thalassemic children die at the age of seventeen.
23.What is Agammaglobulinaemia?
Agammaglobulinaemia is a recessive gene disease, wherein r-globulin synthesis fails to occur. In this disease, the patient shows a great deficiency or total absence of plasma cells and unusual lymph nodes with fewer lymphocytes than normal. The failure of antibody synthesis in this disease, makes the subjects more prone to viral and bacterial infections especially of the chest .This disease mostly affects boys.
24. What is Albinism?
It is an inherited disorder of melanin metabolism characterized by the absence of melanin in the skin, hairs and eyes. The clinical characteristics of this disease are the milk-white coloured skin and marked photophobia. Albinism is an inborn error metabolic disease. The genes by undergoing mutation do not produce particular enzymes, which take part in the metabolic pathways. The metabolism of one amino acid phenylalanine proceeds in chains of enzyme-mediated reactions. The change or absence of enzyme due to defective genes, results in physiological abnormalities. In albinism, complete lack of melanin pigment (a dark brown pigment) causes the albino to suffer. The incidence of albinism in human has been reported to be from 1:5000 to 1:25000. The albinism may be generalized albinism, localized albinism of the eye (ocular albinism) or partial albinism (skin and hair). The recessive genes 'aa' do not produce the tyrosinase enzyme, which converts DOPA (3,4 - dihydroxy phenyl alanine) into melanin in the melanocytes.
25.Explain Huntington's chorea?
This is a fatal disease caused by an autosomal dominant gene in humans. The onset of the disease is between 35 and 40 years of age. It is characterized by uncontrolled jerking of the body due to involuntary twitching of voluntary muscles. It leads to progressive degeneration of the central nervous system accompanied by gradual mental and physical deterioration. The affected gene is located on chromosome 4. Other characteristics of this disease are deterioration of intellectual faculty, depression, occasional hallucination and delusions and other psychological problems. This disease is incurable.