12th Class

Formation of mRNA from DNA is called as Transcription. It is heterocatalytic function of DNA. Template of DNA called sense strand (Master Strand) is involved. The segment of DNA involved in transcriptions is cistron, which have a promoter region where initiation is start and terminator region where transcription ends. Enzyme involved in transcription is RNA polymerase-II. Which consist five polypeptide \[\alpha ,\beta ,{{\beta }^{'}},\omega \] (constitute core enzyme) and \[\sigma \](sigma factor). Sigma \[(\sigma )\] factor recognise promoter site while remaining core enzyme takes part in chain elongation. After transcription, DNA molecule reassociates to form its original structure. In eukaryotes hn RNA (heterogenous nuclear RNA) which consist exon (coded region) and introns (non coded region or intervening sequences) formed in nucleus and diffuse in cytoplasm is also known as split gene which goes to transcription changes for removing the introns and later formed mRNA. It consist three phenomenon (1) Initiation more...

Formation of protein from mRNA is called translation is also known as polypeptide synthesis or protein synthesis. It is unidirectional process. The ribosomes of a polyribosome are held together by a strand of mRNA. Each eukaryotic ribosome has two parts, smaller 40S subunit (30S in prokaryotes) and larger 60S subunit (50S in prokaryotes). Larger subunit has a groove for protection and passage of polypeptide, site A (acceptor or aminoacyl site), enzyme peptidyl transferase and a binding site for tRNA. The smaller subunit has a point for attachment of mRNA. Along with larger subunit, it forms a P-site or peptidyl transfer (donor site). There are binding sites for initiation factors, elongation factors, translocase, GTPase, etc. The raw materials for protein synthesis are amino acids.mRNA, tRNAs and amino acyl tRNA synthetases. Amino acids : Twenty types of amino acids and amides constitute the building blocks of proteins. mRNA : It carries the more...

Variations are differences found in morphological, physiological and cytological behaviouristic traits of individuals belonging to same species race and family. They appear in offspring or siblings due to :

• Reshuffling of genes/chromosomes by chance separation of chromosomes
• Crossing over
• Chance combination of chromosomes during meiosis and fertilization.

Types of variations (1) Somatic variations : These variations influence the somatic or body cells. They appear after birth and are, also called acquired characters, modifications or acquired variations. Somatic variations are non-inheritable and usually disappear with the death of the individual. They are formed due to three reasons i.e., environmental factors, use and disuse of organs, and conscious efforts. (2) Germinal variations : They are inheritable variations formed mostly in germinal cells which are either already present in the ancestors or develop a new due to mutations. Germinal variations are of two types : (i) Continuous variations : more...

Eugenics The term eugenics (Gr. Eugenes, well born) was coined by British scientist Sir Francis Galton in 1883. Galton is called ‘Father of eugenics’ as this branch has been started by him. Eugenics is the branch of science which deals with improvement of human race genetically. Eugenics can be divided into two types : (1) Positive eugenics : In this approach of eugenics the future generations are improved by encouraging the inheritance of better traits. (2) Negative eugenics : This is a negative aspect of improving mankind by restricting the transmission of poor and defective germplasm. Euthenics Euthenics is the improvement of human race by improving the environmental conditions, i.e., by subjecting them to better nutrition, better unpolluted ecological conditions, better education and sufficient amount of medical facilities. Euphenics The study of born defectives and their treatment is called euphenics. The term euphenics was given by A.C. Pai (1974) for more...

Term 'gene' was given by Johannsen (1909) for any particle to which properties of Mendelian factor or determiner can be given. Thomas Hunt Morgan (1910) defined gene as ‘any particle on the chromosome which can be separated from other particles by mutation or recombination is called a gene'. In general, gene is the basic unit of inheritance. According to the recent information a gene is a segment of DNA which contains the information for one enzyme or one polypeptide chain coded in the language of nitrogenous bases or the nucleotides. The sequence of nucleotides in a DNA molecule representing one gene determines the sequence of amino acids in the polypeptide chain (the genetic code). The sequence of three nucleotides reads for one amino acid (codon). Gene action Gene act by producing enzymes. Each gene in an organism produces a specific enzyme, which controls a specific metabolic activity. It means each more...

Recombinant DNA technology Genetic engineering, a kind of biotechnology, is the latest branch in applied genetics dealing the alteration of the genetic make up of cells by deliberate and artificial means. Genetic engineering involves transfer or replacement of genes, so also known as recombination DNA technology or gene splicing. Tools of genetic engineering : Two enzymes used in genetic engineering are restriction endonuclease and ligases. R.E. is used to cut the plasmid as well as the foreign DNA molecules of specific points while ligase is used to seal gaps or to join bits of DNA. Steps of recombinant DNA technology (1) Isolating a useful DNA segment from the donor organism. (2) Splicing it into a suitable vector under conditions to ensure that each vector receives no more than one DNA fragment. (3) Producing of multiple copies of his recombinant DNA. (4) Inserting this altered DNA into a recipient organism. (5) more...

The idea of mutation first originated from the observations of a Dutch botanist Hugo de Vries (1880) on variations in plants of Oenothera lamarckiana. The mutation can be defined as sudden, stable discontinuous and inheritable variations which appear in organism due to permanent change in their genotype. Mutation is mainly of two types : (1) Spontaneous mutations : Mutation have been occurring in nature without a known cause is called spontaneous mutation. (2) Induced mutation : When numerous physical and chemical agents are used to increase the frequency of mutations, they are called induced mutations. Gene mutations Gene or point mutations are stable changes in genes i.e. DNA chain. Many times a change in a gene or nucleotide pair does not produce detectable mutation. Thus the point or gene mutation mean the process by which new alleles of a gene are produced. The gene mutation are of following types : more...

More than two alternative forms (alleles) of a gene in a population occupying the same locus on a chromosome or its homologue are known as multiple alleles. Characteristics of multiple allelism (a) There are more than two alleles of the same genes. (b) All multiple alleles occupy the corresponding loci in the homologous chromosomes. (c) A chromosome or a gamete has only one allele of the group. (d) Any one individual contains only two of the different alleles of a gene, one on each chromosome of the homologous pair carrying that gene. (e) Multiple alleles express different alternative of a single trait. (f) Different alleles may show codominance, dominance-recessive behaviour or incomplete dominance among themselves. (g) Multiple alleles confirm to the Mendelian pattern of inheritance. Examples of multiple allelism : A well known example of a trait determined by multiple alleles is the blood groups in man and skin colour. more...

A pedigree is a systematic listing (either as words or symbols) of the ancestors of a given individual or it may be the "family tree" for a number of individuals. Pedigree analysis is carried out in order to word off possible diaster due to picking up of harmful genetic defects like dominant polydactyly (extra digits), syndactyly (joined digits) and brachydactyly (short digits), recessive haemophilia, deaf mutism, birth blindness, colour blindness, thalassemia, alkaptonuria, phenylketonuria, sickle cell anaemia attached ear lobes, tongue rolling etc. Pedigree chart and symbols : It is customary to represent men by squares and women by circles in a chart for study of pedigree analysis. Marriage is indicated by a connecting horizontal line and the children by attachment to a vertical line extending downward from the horizontal line. Individuals having particular characters to be studied are denoted by solid squares or circles while those not having them are more...

Fixing the sex of an individual as it begins life is called sex determination. The various genetically controlled sex-determination mechanisms have been classified into following categories : Chromosomal theory of sex determination The X-chromosome was first observed by German biologist, Henking in 1891 during the spermatogenesis in male bug and was described as X-body. The chromosome theory of sex determination was worked out by E.B. Wilson and Stevens (1902-1905). They named the X and Y chromosomes as sex-chromosomes or allosomes and other chromosomes of the cell as autosomes. Sex chromosomes carry genes for sex. X-chromosomes carries female determining genes and Y-chromosomes has male determining genes. The number of X and Y chromosomes determines the female or male sex of the individual, Autosomes carry genes for the somatic characters. These do not have any relation with the sex. XX-XY type or Lygaeus type : This type of sex-determining mechanism was first more...