Introduction of Genetics Lecture Notes PDF

Introduction of Genetics Genetics: is a biological science which deals with the principles of heredity and variation. Heredity: refers to the transmission of characters from parents to their offspring. Branches of genetics: 1. Plant Genetics:- It deal with inheritance of characters in variou...

Introduction of Genetics Genetics: is a biological science which deals with the principles of heredity and variation. Heredity: refers to the transmission of characters from parents to their offspring. Branches of genetics: 1. Plant Genetics:- It deal with inheritance of characters in various plants species. 2. Animal Genetics:- A branch of genetics which deals with inheritance of characters and variation of traits in animals. 3. Microbial Genetics:- A branch of genetics which deals with inheritance of characters in micro- organisms like bacteria, viruses and fungi. 4. Molecular Genetics:- A branch of genetics which deals with structure, composition, function and replication of chromosomes and genes. 5. Population Genetics:- A branch of genetics which deals with frequencies of genes and genotypes in a population. 6. Radiation Genetics:- A branch of genetics which deals with effects of radiations on chromosomes and genes. 7. Quantitative Genetics:- A branch of genetics which deals with the inheritance of quantitative characters. 8. Cytogenetics:- Combined study of cytology and genetics. Levels of Genetic Analysis 1. Classical Genetics Identify genes by studying the inheritance of trait differences. Study the structure and behavior of chromosomes. Chromosome mapping by study localization of genes to specific positions within chromosomes Study the transmission of genes and chromosomes from one generation to the next (transmission genetics) 2. Molecular Genetics By discovering DNA structure they can study the replication, expression, and mutation of genes Study of DNA sequences and comparisons to other DNA sequences allow a geneticist to define a gene chemically. 3. Population Genetics Genetics can also be studied at the level of an entire population of organisms. Individuals within a population may carry different alleles of a gene so they determine the frequencies of specific alleles in a population. Application of Genetics:- 1. In Taxonomy Genetic characters like chromosome number and karyotype are taxonomic significance. Karyotype suggests advanced feature of an organism. This gives an idea about the relationship of parental species. Higher the homology, closer is the relationship between two species. 2. In Agriculture The contribution of genetics in the field of agriculture is remarkable in two ways: a- Improvement of crop plants (Yield, Quality, Maturity duration, Resistance to insects, diseases) b- Improvement of Domestic Animals (The milk and meat production and egg production) 3. In Medicine a- Detection of hereditary diseases b- Production of Antibiotics 4. In Evolution Mutagenesis have played significant role in the evolution  Chromosomes These are darkly stained, rod shaped bodies visible under light microscope in a cell during metaphase stage of mitosis  The main features of eukaryotic chromosomes 1. Chromosomes are not visible during interphase under light microscope but are more clearly visible during mitotic metaphase. Hence, they are studied during metaphase. 2. Chromosomes bear genes thus are concerned with transmission of characters from generation to generation 3. Chromosomes vary in shape, size and number in different species of plants and animals. 4. Chromosomes are composed of DNA, RNA and histones. DNA is the major genetic constituent of chromosomes.  All somatic cells of the same species contain an identical number of chromosomes, this represents the diploid number (2n). The haploid number (n) of chromosomes is equal to one-half the diploid number (as in gametes). A genome is a set of chromosomes corresponding to the haploid set (n) of a species. Chromosomes in each cell classified into: 1. Autosomes: all chromosomes exclusive of the sex chromosomes and equal 2n-2 in somatic cell and n-1 in gametes. 2. sex chromosomes which are heteromorphic pair of chromosomes called (XX and XY) and equal 2 in somatic cell and 1 in gametes.  With the exception of sex chromosomes, each chromosome exists in pairs with same length and centromere placement, identical features and the members of each pair are called homologous chromosomes. They contain identical gene sites (locus) along their length. One member of each pair is derived from the maternal parent (through ovum) and the other member is derived from the paternal parent (through the sperm). Chromosome Morphology Each chromosome consists of seven parts: (1) Centromere (2) chromatids (3) secondary constriction and satellite (4) Telomere (5) chromomere (6) Chromonema (7) matrix Centromere (primary constriction or kinetochore) The region of chromosome with which spindle fibers are attached during metaphase. Chromatid One of the two distinct longitudinal subunits of a chromosome which get separated during anaphase. Two chromatids of a chromosome are held together by centromere. After separation at anaphase each chromatid becomes a chromosome. Telomere The terminal region of a chromosome on either sides. Maintain the stability of chromosome (telomere of one chromosome cannot unite with the telomere of another chromosome). Secondary Constriction It has constant position and, therefore, can be used as useful marker. Chromomeres It is bead like structures found on the chromosomes. Chromonema thread like coiled structures (DNA thread) and it is the gene bearing portion of chromosomes Matrix o A mass in which chromonema are embedded. o Matrix is enclosed in a sheath which is known as pellicle. o Both matrix and pellicle are non genetic materials. Classification of Chromosomes in relation to position and number of centromere Chromosome Number of Chromosome Position of centromere type centromere type Metacentric: The centromere is at the centre. Nil Acentric Sub metacentric: The centromere is a little away One Monocentric from the centre. Acrocentric: The centromere is nearer to one Two Dicentric end. Telocentric: The centromere is at the end. Three Tricentric Chromosome has two arms