Genetics 1

• Few significant ideas were put forward to explain heredity during prehistoric times
• 1600-1850: Dawn of Modern Biology
• William Harvey -> Theory of Epigenesis: Structures such as body organs are not initially present in the early embryo and are formed later on
• Schleiden and Schwann -> The Cell Theory (1830): All living organism are made of cells
• Charles Darwin’s travels on the HMS Beagle provided him geological, geographical, and biological observation that helped formulate his theory of evolution. He noticed the diversity of living things all around him
• Darwin published his ideas on evolution theory in The Origin of Species (1859)
• Existing species arose from other ancestral species by descent with modification

  Natural selection was the driving force for evolutionary change

  Independently proposed by Alfred Russel Wallace
• Genesis - birth
• Genetics - Study of birth or study of heredity
• Branches of genetics 

  • Transmission
  • Molecular
  • Population
• Gregor Mendel (1822-1884)

  • Experiment on pease (1866)
  • Inheritance - particulate, each parent contributes particles, factors or genes, phenotype (appearance)
  • Genes exist in several different forms (alleles)
  • Dominance, recessiveness
• Mendel published his findings on the transmission of genetic information from parents to offspring

  Mendeal worked with peas and used quantitative data to support his ideas
• In mitosis, chromosomes are copies and distributed so that the 2 resulting daughter cells each receive a diploid set

  In meiosis, resulting cells (gametes) receive only half the number of chromosomes and are haploid
• According to the chromosomal theory of inheritance, inherited traits are controlled by genes residing on chromosomes. These genes are transmitted through gametes. This maintains genetic continuity from generation to generation.
• Mutations produce alleles of a gene, they are the source of genetic variation.
• The set of alleles for a given trait is called the genotype
• The expression of the genotype produces an observable trait or phenotype
• DNA, not protein, is the carrier of genetic information (research of Avery, MacLeod, and Mccarty in 1944)
• Thomas Hunt Morgan (1910)

  • Chromosome theory of inheritance
  • Worked on fruit flies (drosophila melanogaster)
  • Sex and eye color
  • Autosomes
  • Genotype
  • Sex chromosomes
  • Wild type or standard type
  • Mutant
• 23 sets of chromosomes, 22 pairs are autosomes, 1 pair are sex chromosomes
• Wild- Normal, mutant- abnormal
• Transmission genetics -> genetic recombination and mapping
• Recombinants - crossing over
• A.H. Sturtevant - space between the genes
• 1930 - genetic mapping with eukaryotes like peas, humans, neurospora, a mold, and in prokaryotes
• Barbara McClintock

  • Demonstrated crossing over in 1931
  • Direction relationship between region of a chromosome and gene
• 1869 - Friedrich Miescher - nucleus is a mixture of compounds called nuclein

  Miescher collected bandages from nearby hospitals and studies the pus under a microscope
• Deoxyribonucleic acid - DNA

  Ribonucleic acid - RNA
• Oswald Avery & colleague - 1944

  • Pieces of DNA
  • Frederick Griffith 1920’s rediscovered
• Archibald Garrod 

  • Human disease
  • Alkaptonuria
  • Recessive trait disease
  • Accumulation of black pigment in the urine
• Biochemical pathway - abnormal build up of an intermediate chemical compound
• Biochemists - shown several chemical reactions carried out by cells
• Reactions are accelerated by organic catalysts - Enzymes (proteins)
• Garrod’s conclusion: defective gene gives rise to defective enzyme
• 1941 - George Beadle and E. L. Tatum proved the relationship between genes and enzymes. Mutagens - mutation. Worked on Neurospora.
• What do genes do?

  • Replicate faithfully
  • Direction production of RNAs and proteins
  • Accumulate mutations and so allow evolution
• James Watson and Francis Crick - 1953

  • Discovered the structure of DNA
  • Explained how DNA replicates
  • Used the data from Rosalind Franklin and Maurice Wilkins
  • Nobel prize 1962
• Genetic code

  • Marshall Nirenberg (1927-2010) 
  • Har Gobhind Khorana (1922-2011) in 1960s
  • Mutations
  • Gene cloning
  • Human genome project
  • Stem cell research
• Population genetics

  • Examines the extent of genetic variations within and among populations
  • Describes genetic differences between species
  • Learning about the process of species formation
  • Genetic counseling
• DNA is an antiparallel, double-stranded helix. Its monomer is a nucleotide consisting of a sugar (deoxyribose) bonded to a phosphate and also bonded to the bases adenine, cytosine, guanine, and thymine. These nucleotides form A-T and G-C complementary base pairing across the helix.