Biology Blogs For Class11th, 12th and NEET

                                                                                                       Ames Test  Bruce Ames develops a method to  test the chemicals for cancer causing properties .  The test is based on the fact that  any thing that is mutagenic may also turn out to be a carcinogen, that is to cause cancer . The assay is based on the reversion of the mutation in the histidine operon in the genetically altered tester strains of bacterium Salmonella typhimurium . The his peron encodes enzymes required for the biosynthesis of the amino acid hitsidine . Strains with mutations in the his operon are histidine auxotrophs . However , the mutation can be reversed , a back mutation , with the gene regaining its function . These revertants are able to grow on a medium lacking histidine . The tester strains are specially constructed to have both  frame shift and point mutation in the genes required to synthesize histidine , which allows for the detection of mutagens acting

                                   Lampbrush Chromosomes  In 1882 Flemming first  observed this type of chromosomes in oocyte of amphibians . In the meiotic prophase stage of diplotene this oocyte is developed  due to active transcription of many genes .  The chromosomes  is consist of two pair of sister chromatids held together by chasmata therefore this are also known as Bivalant structure of meiosis .   Lampbrush chromosomes are easily visible in light microscope where they organised in the form of large extended loops and this loops are surrounded by a matrix of ribonucleotide proteins that contain nascent RNA chains . Lambrush chromosomes are thought to assist in fulfilling the high demand for transcripts during oogenesis .   

                                    Types of Meiosis  Meiosis and  fertilization are the two important aspects of sexually reproducing organisms . A in every sexual producing individual fertilization and the process of meiosis are the two alternative phases of life and through this, they maintaining the constant number of chromosomes from one organism to another.  Although fertilization and meiosis timing may vary in species to species the process is common in all sexually reproducing organisms.  so,  on these basis meioses can be of three types - Gametic  zygotic  sporogenic  Gametic - Gametic type of meiosis occurs in the formation of gamete which is haploid in nature. The gamete further gives rise to a diploid zygote. This zygote by mitotic division changed into an organism.  This type of division is generally seen in humans. Zygotic   -   Zygotic type of meiosis is generally seen in algae and fungi where meiosis division does not occur during gamete formatio

                     Gram-Positive Bacteria & Gram-Negative   Bacteria have a cell wall made up of polysaccharides known as Peptidoglycans which gave them strength and rigidity and this is important since bacteria observe some osmotic pressure due to the variation of different solutions they encounter and their cell wall which prevents the cell from shrinking or swelling. So , on the basis of the cell wall and the pattern of gram staining, bacteria are classified into two categories - Gram-Positive and Gram-Negative. Gram-positive bacteria  have double-thick walls which consist of around 30 layers of peptidoglycan and surrounds a single plasma membrane.  They do not have an outer cell membrane but have a complex cell wall made up of teichoic acid.  For example - Staphylococci.   Gram-negative bacteria  have a much thinner cell wall consisting of peptidoglycans having high lipid content. The peptidoglycan is a present between the two lipid layer called Dye terms . Also, the