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PBG 707 lectures
Cytogeneticists
The people who choose the field of cytogenetic
Cytogenetics
It is a hybrid name cytology + genetics. It deals with the study of heredity through the methods of cytology and genetics This science is concerned with the structure, number, function and movement of the chromosome and the numerous variations of these prosperities as they relate to the transmission, recombination and expression of the gene. It also deals with the non chromosomal heredity factors. To fully under stand the history of cytogenetic, one has to look at its root. Consequently history includes cytology, genetics and cytogenetic. The men who choose this field to dig the history of cytogenetic did a lot of work and made significant contribution. The people belong to different fields and were leading physicists, microscopists, physiologists, morphologists, embryologists’ and medical doctors. We ask ourselves the questions “what is chromosome?” “What does it do?” “Why does it do” “what it does” these activities are happening in an organized cellular environment. We must understand cytological and cytogenetically basis of higher forms of life and microorganisms and viruses.
Microscopes
Microsoft and its different types
i. Simple microscope ii. Compound microscope iii. Acoustic microscope iv. Electron microscope v. Phase contrast microscope vi. Phase difference microscope vii. Reflecting microscope viii. Ultraviolet microscope
ix. Infra red microscope x. Fluorescent microscope xi. Disecting or stereo microscope xii. Confocal microscope xiii. Transmission electron microscope (TEM) xiv. Scanning Electron microscope (SEM)
Microscope
Greek word Mikros mean little or small skopeein to view or to look to. It is an instrument for magnifying the minute objects able to see minute objects, invisible or hardily visible without the aid of microscope
Simple microscope
Microscope with one simple lens
Compound microscope
Microscope with two or more lenses
Acoustic microscope
One in which ultra sonic waves pass through the specimen
Electron microscope
One using the beam of electron
Phase contrast microscope
It is a device which causes a difference of refractive index between an object and surrounding medium to be visible in an ordinary form of a black and white image.
Phase difference microscope
Reflecting microscope
To bend or sent back, to through back after striking, to give an image of in the manner of a mirror
Ultraviolet microscope
One using a beam of ultra violet rays
Infra red microscope
Fluorescent microscope
Disecting or stereo microscope
It is light illuminated. The image is in 3D used to look large specimen as it has low magnification. You can not see the details of the individual, small cells as it has low magnification
Confocal microscope
Laser beam is used. The laser light scans through the specimen with the addition of scanning mirrors. The image is then placed on the digital computer screen for analysis
Transmission electron microscope (TEM)
This gives the 2D image. Thin slices of specimen are obtained. The electron beam pass through the higher magnification, higher resolution electronically illuminated.
Scanning Electron microscope (SEM)
1879 Flemming 1882 Flemming 1834-1914 Weisman 1817-1891 Nageli Swis 1844-1912 Strasburger German 1840-1908 Ernst Abbe German Physicists 1860-1915 Boveri German 1876-1908 Sutton America 1861-1926 Bateson (1902, 1906, 1907) British 1889-1938 Bridges 1884-1955 Feulgen
Johannes, Sacharianen, Zachrius and Janssen
Dutch eye glass maker between the years 1608 produced the 1st^ optical compound microscope. They combined two convex lenses in a tube, the magnification was not more than 10 times but it was a great excitement.
Robert hooke (1635-1703)
Introduce the term cell. Describe the cork and other cells. Microscope at that time magnified 100-200 times with distortion of shape and colour. For better clarity more magnification was required.
Camerarius (1665-1771)
Reported the existence of sexual reproduction in plants. He said maize seeds are not produced unless pollen is applied to the pistle. Credited by producing 1st hybrid plant by crossing the Hamp with Hop.
Kolreuter (1733-1806)
Produced tobacco hybrids. Most important observation in reciprocal crosses showed equal contribution of both the parents.
Robert Brown 1828
Discovered the cell nucleus in flowering plants (Tradescantia). He also discovered the random thermal motion of small particle still known as Brownian movement.
Mohal 1835
Known as creator of modern cytology. In 1835 described cell division and emphasize the importance of protoplasm. He also said that cell in algae and higher plants are arising through partition wall being formed between pre existing cells.
Schleiden and Schwann (1804-1881)
They proposed the cell theory which states cell is a unit of biological organization
Schleiden 1838
He discovered the nucleolus in the cell
Schwann
He invented the term cell theory in 1838. Actually it was the work of schleiden to which he agreed in total with these three refinements.
a. Cell is the smallest building element and as a unit in elementary organism b. Each cell has a special task to accomplish. c. A cell can only be produced from an other cell by a remarkable process of cell division
Virchow 1821-
German professors give a Theory of cell lineage, it mean cell arise from pre existing cells and confirmed the idea of Schleiden and Schwann
Mendal 1822-1884 Austrian
Father of genetics 1866 publish his work Give two laws of inheritance Three scientist Corens, Devries, Tschermak found the similar results
Frederick Miescher 1884-
Swiss chemist isolated the nucleic acid, nucleo protein in1871. He got the puss cells in suspension and by treatment with the dilute HCL, Pepsin and ether so separated the nuclei from every thing else. From these nuclei he prepared a substance of remarkable prosperities named as nucleic acid which later known as DNA. Miescher work on winter Salmon fish in the isolated head of the sperm he not only nucleic acid but a high basic nitrogenous substance to which he gave the name of protamine. When protamine is combined with nucleic acid, the compound is called as nucleoprotein
Herintwig 1849-
In 1876 and 1877 he studied the reproduction in sea urchin and calculated the fertilization involve the union of the sperm and egg. This study actually iniated the period of experimental cytology.
Flemming 1842-1915 Austrian cytologist.
In 1882 proposed the term mitosis. He also showed the chromosome longitudinal splitting during nuclear division and the formation of the daughter nuclei. He also applied the name of the chromatin to the stainable protein of the nucleus in 1879 Flemming described mitosis in living cells and fixes the cells of salamander. Important contribution is development of fixing and staining technique which made cytological details possible. In 1882 Flemming studied the human chromosome complement.
- 1/100th^ of the eukaryotic DNA
- DNA thinly coated with protein involved in a folding process and also enzyme require for repair, recombination and transcription.
- Some viruses contain RNA as the genetic material.
- These are much simpler structures when compared with eukaryotic chromosome.
- Examples are viruses and bacteria
- There are two types of extra nuclei DNA
B. Eukaryotes
- Chromosome is enchased in ratio of 2:1 mean two proteins and one DNA.
- These proteins consist of 5 major histones and very heterogeneous mixture of 30 non histones protein called HMGs, (High Mobility Group protein) and some associated RNA this mixture as a whole termed as chromatin.
- Examples are human cells plant cells.
Organization of the Chromatin
Chromatin is organized on the four basic levels
- Primary structure Nucleosome
- Secondary Structure Solenoids
- Tertiary Structure Loops
- Quaternary Structure Final folding into chromosome
Primary nucleosome and secondary solenoid the 1st^ two are well established however the other two are poorly understood and still are controversial
Nucleosome
Nucleosome is a fundamental unit of chromatin when DNA is subjected to osmotic shock it unwinds to give a beaded string appearance. The beads are essentially composed of histones protein, the protein are universally associated with nuclear DNA in eukaryotes and represents some of the most evolutionary conserved protein each histones contain hydrophobic core region with one or two basic arms
