Genetics Lec 1: Third Class PDF

Genetics Lec 1: Third Class Introduction: Genetics: is the science that studies inherited traits, their variation, and their transmission from one generation to another. It is a division of the science of Biology; therefore, it was closely related to the develop...

Genetics Lec 1: Third Class Introduction: Genetics: is the science that studies inherited traits, their variation, and their transmission from one generation to another. It is a division of the science of Biology; therefore, it was closely related to the development of biology and the instruments used in biology. Nucleic acid structure:- -Nucleic acid structure refers to the structure of nucleic acids such as DNA and RNA. DNA and RNA are very similar. Nucleic acids (DNA, RNA) are the materials of genetics , genetic information are stored in DNA. DNA is a polymer of nucleotides, organized in a double helix structure, and present as chromosomes in the nuclei (single: nucleus) of cells. There are 2 types of cells – Prokaryotic cells: bacteria, Not separated from the cytoplasm in prokaryotes present in the (nucleoid). –Eukaryotic cells: unicellular organisms, multicellular organisms like fungi, animals, plants, humans. The genetic material present in the nucleus surrounded by nuclear membrane in eukaryotes. Human body contains trillions (10^9) of cells-Eukaryotic cells, Genetics Lec 1: Third Class DNA stores the genetic information; it is arranged as chromosomes in the nucleus and mitochondria. Every species has a unique number of chromosomes called the diploid number (2n). Human cell contains 46 chromosomes (23 pairs). Somatic cells have the complete number (2n) of chromosomes (23 pairs) Chromosome pairs are numbered: a) 1-22 (autosomal chromosomes (autosomes)) b) 2 sex chromosomes, X and Y (XX in female, XY in male) For every chromosome there are 2 copies, called Homologous chromosomes (or homologs): –One comes from the mother –One comes from the father Homologous chromosomes have alleles for the same gene at a specific locus. Genetics Lec 1: Third Class Cell Division : There are two types of cell division: –Mitosis: occurs in somatic cells –Meiosis: occurs in gametes during gametogenesis Mitosis: chromosomes should duplicate in number before division to maintain the diploid number of chromosomes in daughter cells Meiosis: the chromosome number is halved (reduced from diploid number (2n) to haploid number (1n) to maintain the diploid number from one generation to another During Fertilization, the diploid number of chromosomes (2n) is restored by mating between an ovum and a sperm. Genetics Lec 1: Third Class Cell Cycle: The continuity of life depends on cells growing, replicating their genetic material, and then dividing, a process called the cell cycle. Cell cycle: a series of events and activities that prepares the cell for division, Cell cycle rate varies in different tissues at different times. Phases of Cell Cycle : Cell cycle is divided into 2 major phases: 1. Interphase: the stage of cell growth and metabolic activities, occupies most of the time of cell cycle (90% of cell cycle) Which is subdivided into 3 phases: – G1-phase (Gap 1) – S-phase (DNA Synthesis) – G2-phase (Gap 2) 2. M-phase (Mitotic): cell division, lasts for 2-3 hours Genetics Lec 1: Third Class Cell Cycle According to dividing ability, cells of the body can be classified into 3 types: 1. Cells that divide throughout their life time, e.g. cells in the epidermis (skin). 2. Cells that stop dividing but can resume division on need, e.g. liver cells stop dividing when the liver reaches its normal size, but the cells start dividing again when if the liver is injured or a piece was cut. 3. Cells that stop dividing for the rest of their life, e.g. neural and muscle cells.