GENETICS

• Central Dogma


  Describes the flow of genetic information from DNA to RNA to protein
• Central Dogma of Life

  1. Replication (DNA is duplicated)

  2. Transcription (DNA is encoded into RNA)

  3. Translation (RNA is encoded into protein)
• DNA


  • Composed of phosphate groups, five carbon sugars (deoxyribose), and nitrogen-containing bases (purines and pyrimidines)
  • Double-stranded helix with antiparallel strands
  • Nucleotides in each strand linked by 5'-3' phosphodiester bonds
  • Bases on opposite strands linked by hydrogen bonding: A with T, and G with C
• DNA Replication


  1. DNA helicase unwinds parent DNA strands

  2. RNA polymerase (primase) constructs RNA primer

  3. DNA polymerase III adds complementary nucleotides to leading strand

  4. Lagging strand synthesized discontinuously as Okazaki fragments

  5. DNA ligase seals fragments in lagging strand
• Transcription


  1. RNA polymerase synthesizes complementary RNA strand against DNA template

  2. Thymine replaced by uracil as complementary nucleotide to adenine
• Translation


  1. mRNA carries genetic information to ribosomes

  2. tRNA transports amino acids to ribosomes

  3. rRNA helps build ribosomes where protein synthesis occurs

  4. Start and stop codons mark beginning and end of polypeptide sequence
• Gene


  A unit of heredity; a section of DNA sequence encoding a single protein
• Genome


  The entire set of genes in an organism
• Alleles


  Two genes that occupy the same position on homologous chromosomes and cover the same trait<|>Dominant alleles represented by capital letters, recessive alleles by lowercase letters
• Homozygous


  Having identical genes (one from each parent) for a particular characteristic
• Heterozygous


  Having two different genes for a particular characteristic
• Dominant


  The allele of a gene that masks or suppresses the expression of an alternate allele
• Recessive


  An allele that is masked by a dominant allele; does not appear in the heterozygous condition, only in homozygous
• Genotype


  The genetic makeup of an organism
• Phenotype


  The physical appearance of an organism (Genotype + environment)
• Locus


  A fixed location on a strand of DNA where a gene or one of its alleles is located
• Genes and Chromosomes


  • Gene is a unit of heredity that transmits genetic information
  • DNA coils around histones to form nucleosomes, which group into chromatin fibers and chromosomes
  • Humans have autosomal and sex chromosomes, some traits are sex-linked
• 1. Linked Dominant Inheritance


  • Trait never passed from father to son
  • All daughters of affected male and normal female are affected
  • All sons of affected male and normal female are normal
  • Females more likely affected than males
  • Some X-linked dominant diseases lethal for males
• 1. Linked Recessive Inheritance


  • Trait never passed from father to son
  • Males more likely affected than females
  • Trait passed from affected grandfather, through carrier daughters, to half of grandsons
• Sex-linked inheritance


  Inheritance of traits determined by genes located on the sex chromosomes
• Types of sex-linked inheritance

  • X-Linked Dominant Inheritance
  • X-Linked Recessive Inheritance
  • Y-Linked Inheritance
• 1. Linked Dominant Inheritance


  • Trait is never passed from father to son
  • All daughters of an affected male and a normal female are affected
  • All sons of an affected male and a normal female are normal
  • Females are more likely to be affected than males because the X as their dominant allele
  • Some X-linked dominant diseases are lethal for males
• 1. Linked Dominant Inheritance


  • hypophosphatemia
  • Aicardi syndrome
  • fragile X syndrome
• 1. Linked Recessive Inheritance


  • Trait is never passed from father to son
  • Males are more likely to be affected than females
  • Trait or disease typically passed from an affected grandfather, through carrier daughters, to half of his grandsons
• 1. Linked Recessive Inheritance


  • red and green colorblindness
  • hemophilia
  • Duchenne muscular dystrophy
  • hunter syndrome
• 1. Linked Inheritance


  • When a male is affected, all of his male children are affected
• 1. Linked Inheritance


  • male infertility
  • pattern baldness
  • hypertrichosis pinnae
• Autosomal inheritance


  The gene for a specific trait is carried by autosomal chromosomes
• Types of autosomal inheritance

  • Autosomal Dominant Inheritance
  • Autosomal Recessive Inheritance
• Autosomal Dominant Inheritance


  • Males and females are equally affected
  • Every affected individual has at least one affected parent
  • Affected individuals mating with unaffected individuals have at least a 50% chance of transmitting the trait of each child
  • Two affected individuals may have unaffected children
  • Phenotype generally appears every generation
• Autosomal Recessive Inheritance


  • Males and females are equally affected
  • Affected individual may have unaffected parents
  • All children of two affected individuals are affected
  • Phenotype may skip a generation
• Chromosomal abnormalities occur during early fetal development during movement of chromosomes in cell division of the embryo
• Chromosomal abnormalities can be influenced by several factors such as drugs, alcohol, or presence of a gene that could suppress expression of other genes
• Common chromosomal abnormalities


  • Down syndrome (extra copies of autosome no. 21)
  • Klinefelter syndrome (extra X chromosome, XXY)
  • Turner syndrome (missing X chromosome, XO)
• Many chromosomal abnormalities have psychological impact due to mental disabilities, like with Down syndrome
• Karyotyping


  A technique applied in biology to determine chromosomal abnormalities
• Pedigree Analysis


  A technique used to predict the occurrence of a certain traits within a family
• Mutation


  Alteration of the DNA nucleotide sequences that can affect the expression of a gene or trait of an individual
• Types of mutation


  • Gene mutation
  • Chromosomal mutation
• Types of gene mutation

  • Point mutation
  • Frameshift mutation