CYTOGENETICS (2nd sem midterm)

• Learning Objectives: '1. Explain the general concept and principles related to cytogenetics. 2. Differentiate terms commonly employed in the study of genes. 3. Identify the pioneers in cytogenetics and their contribution. 4. Enumerate the three main areas in the study of genetics and their areas/field.'
• Cytogenetics


  • A branch of genetics that deals with the study of inheritance in relation to the structure and function of chromosomes
• Topics in Cytogenetics


  • Nucleic Acid
  • Chromosome and genes
  • Cell cycle
  • Mendelian patterns of inheritance
  • Chromosomal abnormalities and diseases
  • Cytogenetic Techniques
• Character


  Heritable feature that varies among individuals
• Trait


  Pertains to each variant for a character (Ex: flower color: purple or white)
• True Breeding


  Parents would produce an offspring that would carry the same phenotype
• Hybridization


  Mating or crossing of two varieties
• Genotype


  Genetic composition of an organism
• Phenotype


  The visible expression of information contained in a gene
• Locus


  Specific, fixed position on a chromosome where a particular gene is located
• Allele


  Alternative form of a gene
• Homozygous


  An organism having a pair of identical alleles at a given locus on a given chromosome
• Heterozygous


  An organism having two different alleles at a given locus
• Genes


  A nucleotide sequence coding a polypeptide sequence which makes an enzyme or structural protein
• General beliefs of Hippocratic school persisted (Gametes of the organism would assemble into the individual)
• Nicolas Hartsoeker (1694) introduced the concept of Homunculus: a miniature human carried in the head of a sperm
• William Harvey proposed the theory of epigenesis
• Robert Hooke (1665) observed the cell structure under a light microscope
• Anton Van Leeuwenhoek (1674-1683) was a master lens maker who developed a single-lens microscope
• Jan Purkinje (1830) first described the nucleus within a cell
• Robert Brown (1831) coined the term nucleus and observed Brownian motion of microscopic particles
• Hugo von Mohl (1835-1839) studied mitosis in a cell
• Rudolf Virchow (1858) summarized the concept of cell theory ("Omnis cellula e cellula": all cells come from preexisting cells)
• Gregor Mendel (1856-1863) conducted classical hybridization experiments with pea plants and studied statistical patterns of heritable phenotypes
• Oscar Hertwig (1875) studied the fusion of sperm and egg to form a zygote
• Walther Flemming (1879-1885) used newly synthesized aniline dyes to view and describe chromosomes and their movement during mitosis
• Heinrich Waldeyer (1888) first used the term chromosome
• Theodor Boveri, Karl Rabl, and Edouard van Beneden (1880) hypothesized that chromosomes are individual structures with continuity from one generation
• August Weismann (1885) proposed that inheritance of traits is based exclusively in the nucleus and described meiosis in 1887
• Hertwig and Boveri (1890) described the process of meiosis in detail
• Thomas Hunt Morgan (1900) introduced Drosophila melanogaster as a model genetic system
• Walter Sutton (1902) explained Mendel's rules of inheritance
• Nettie Maria Stevens (1905) investigated sex determination in mealworms and studied X and Y chromosomes
• Chromosome Theory and Sex Linkage

  1. Thomas Hunt Morgan (1900) introduced Drosophila melanogaster as a model genetic system

  2. Walter Sutton (1902) explained Mendel’s rules of inheritance

  3. Nettie Maria Stevens (1905) investigated sex determination in mealworms; X and Y chromosomes

  4. Thomas Hunt Morgan (1911) genes producing white eyes, yellow body, and miniature wings in Drosophila are located on the X chromosome

  5. Alfred Sturtevant (1913) used Drosophila to create the first genetic map

  6. Calvin Bridges (1914) working with Morgan; described nondisjunction of Drosophila sex chromosomes
• Chromosome Theory and Sex Linkage

  1. Lewis Stadler and Hermann Muller (1927) genes can be mutated artificially by X-rays

  2. William Bateson (1902) terms f1, F2 homozygote, heterozygote, and allelomorph; created the term genetics (1905)

  3. Wilhelm Johannsen (1909) phenotype, genotype, and gene

  4. Ronald A. Fisher, Sewall Wright, and John B.S. Haldane (1930-1932) algebraic foundations for our understanding of the process of evolution
• DNA, RNA and Molecular Genetics

  1. Oswald Avery (1944), Alfred Hershey and Martha Chase (1952) DNA was the genetic material

  2. James Watson and Francis Crick (1953) worked out the structure of DNA

  3. Werner Arber, Hamilton Smith, and Daniel Nathans (1968-1973) described restriction endonucleases as “the servant with the scissors” (Nobel Prize in 1978)

  4. Paul Berg (1972) first to construct a recombinant DNA molecule containing parts of DNA from different species
• DNA, RNA and Molecular Genetics

  1. 1995: Haemophilus influenzae was the first organism to have its complete genome sequenced

  2. 1996: first mammal was cloned (Dolly) by Ian Wilmut

  3. 1997: first transgenic cow (Rosie), can express human –lactalbumin protein in her milk

  4. 2001: human genome was sequenced and published

  5. September 2007: 634 different organisms have had their complete genome sequenced and published
• Classical Genetics


  1. Concerned with genes, mutations and phenotypes

  2. Deals with the arrangements of genes on the chromosome, methods that generate mutations and various patterns of inheritance

  3. Gregor Mendel published the basic rules of inheritance (1866)

  4. Correctly hypothesized that traits such as pod color were controlled by genetic elements

  5. Predicted that adult organisms have two copies of each gene (diploid state); gametes receive just one of these copies (haploid state)

  6. Formulated two general laws of inheritance: law of segregation and the law of independent assortment
• Classical Genetics


  1. Chromosomal theory of inheritance: Chromosomes, which contain genes, are the carriers of the genetic material

  2. George Beadle and Edward Tatum (1940) suggested that one gene encodes one enzyme (“one-gene-encodes-one-polypeptides”)

  3. Application of Classical Genetics: Pedigree Analysis – pictorial representation of related individuals and the phenotype that each exhibits

  4. Karyotyping – is the representation of all the chromosomes in an individual
• Molecular Genetics


  1. Molecular Genetics – study of the structure, replication, and expression of the genetic material and of the expressed protein

  2. DNA (Deoxyribonucleic Acid): Genetic material for all cellular organisms, Double-helical molecule, Anti-parallel, Bases: adenine (A), thymine (T), guanine (G) and cytosine (C)

  3. DNA Replication: Double helix, DNA polymerase