BIO 1 Principles of Genetics PDF

Republic of the Philippines CENTRAL BICOL STATE UNIVERSITY OF AGRICULTURE San Jose, Pili, Camarines Sur 4418 Website: www.cbsua.edu.ph Email Address: [email protected]...

Republic of the Philippines CENTRAL BICOL STATE UNIVERSITY OF AGRICULTURE San Jose, Pili, Camarines Sur 4418 Website: www.cbsua.edu.ph Email Address: [email protected] Trunkline: (054) 871-5531;871-5533 BIO 1 – PRINCIPLES OF GENETICS CHAPTER 1: PHYSICAL BASIS OF INHERITANCE CHROMOSOMES Are structures within living cells that contain the genetic material. The term chromosome means “colored body”. Genes are physically located within chromosomes. thread-like structures present in the nucleus. These are present inside the nucleus of plants as well as animal cells. Chromosomes were first discovered by Strasburger in 1815 and the term ‘chromosome’ was first used by Waldeyer in 1888. Human beings have 46 chromosomes in their body. These are arranged into 23 pairs. The 22 pair of chromosomes are the autosomes while the 23rd pair is the sex chromosomes. “A Chromosome looks like a thread and is coiled material, made of proteins. Chromosomes are present in the nucleus of all the cells and contain the basic genetic material DNA, which passes from one generation to another”. CHROMOSOMES FUNCTIONS It provides genetic information for cellular functions of organisms. It protects genetic material (DNA) from damage during cell division. They ensure a precise distribution of DNA to daughter nuclei during cell division Prokaryotic Chromosomes The DNA of prokaryotes (bacteria is one, circular chromosome attached to the inside of the cell membrane Eukaryotic chromosomes All eukaryotic cells store genetic information in chromosomes  Most eukaryotes have between 10 and 50 chromosomes in their body cells Human body cells have 46 chromosomes or 23 identical pairs Each chromosome is composed of a single tightly coiled DNA molecule Chromosomes can’t be seen when cells are dividing and are called chromatin CHEMICAL CONSTITUENTS DNA RNA Histones (basic in nature) Non-histone proteins (acidic in nature) STRUCTURE OF ONE CHROMOSOME Centromere or Kinetochore: It is the primary constriction at the center to which the chromatids or spindle fibers are attached. Its function is to enable movement of the chromosome during the anaphase stage of cell division. Chromatid During cell division, a chromosome is divided into 2 identical half strands joined by a centromere. A chromatid is each half of the chromosome joined. Each chromatid contains DNA and separates at Anaphase to form a separate chromosome. Both chromatids are attached to each other by the centromere. BIO 1_Principles of Genetics Page 2 of 4 Chromatin It is a complex of DNA and proteins that forms chromosomes within the nucleus of eukaryotic cells. Nuclear DNA is highly condensed and wrapped around nuclear proteins in order to fit inside the nucleus. The chromatin consists of DNA, RNA, and protein. TYPES OF CHROMOSOMEs Homologous chromosomes pertain to two chromosomes which are same, at least in terms of the gene sequences and loci. Heterologous (non-homologous) chromosomes pertain to any two chromosomes that are different, such as in terms of gene sequence and loci. CLASSIFICATION OF CHROMOSOMES According to position of the centromere: Metacentric Chromosomes: - the centromere present exactly in the center. - chromosomes are therefore of equal length. - Example: Human chromosome 1 and 3 Submetacentric Chromosomes: - the centromere is not present exactly at the center. - centromere is slightly offset from the center. - Both the sections are therefore not of equal length or are asymmetrical. - Example: Human chromosomes 4 to 12. Acrocentric Chromosomes: - have a centromere which is highly offset from the center. - one of the strands is very long and one very short. - Example: Human chromosomes 13,15, 21, and 22 Telocentric Chromosomes: - the centromere is present at the very end of the chromosome. - present in species such as mice. CHROMOSOME NUMBER Two types: 1) Somatic chromosome number (2n): any chromosome that is not a sex chromosome; appear in pairs in body cells but as single chromosomes in spermatozoa. BIO 1_Principles of Genetics Page 3 of 4 2) Gametic chromosome number (n): any of the chromosomes contained in a haploid cell, specifically a spermatozoon or an ovum, as contrasted with those in a diploid, or somatic, cell CHROMOSOME SIZE Shows variation depending upon stage of cell division. Longest and thinnest chromosome seen during interphase. In prophase, decreases in length with an increase in thickness. Smallest chromosome seen during anaphase Number of Chromosomes of different Organisms Organisms Number of Chromosomes Human 46 Pig 38 Cow 60 Chicken 78 Duck 80 Domestic Horse 64 Fruit fly 8 Monkey 48 Swamp buffalo 48 Dolphin 44 Onion 16 Rice 12 References: - https://www.kgmu.org/digital_lectures/medical/anatomy/dr.archana_rani_chro mosomes.pdf - https://www.toppr.com/guides/molecular-genetics/chromosome/ BIO 1_Principles of Genetics Page 4 of 4