genetics

• multifactorial inheritance?

  • inheritance controlled by many genes with small additive effects (polygenic) & effects of environment
• 3 types of genetic disorders?

  1. multifactorial
  2. chromosomal - 0.6% live born
  3. single gene - 1% live born
• explain multifactorial inheritance?

  • environmental influence & genetic predisposition - susceptibility to disease
  • one organ system affected
• chromosamal GD?

  • thousands of genes may be involved
  • multiple organ systems affected at multiple stages in gestation
  • ususally spontaneous
  • deletions/duplications
  • can be inherited - translocation
  • chromosamal imbalance cause alteration in gene dosage
• single GD?

  • dominant/recessive pedigree patterns
  • mutations in single genes
  • can affect structural proteins/enzymes/receptors
  • often cause loss of function
• chromosomal abnormalities?

  • numerical - gain/loss of complete chromosomes
  • serious & often lethal consequences - autosomal anomalies
  • autosomal monosomies are catastrophic
  • fewer serious effects from sex chromosome anomalies
• explain single gene disorder?

  • mutation to dna sequence of gene causes effects to mrna sequence - amino acid sequence
  • high risk to relatives
  • dominant/recessive pedigree patterns
  • changes structural proteins/enzymes/receptors/tf
• inheritance patterns?

  1. autosomal dominant
  2. autosomal recessive
  3. x linked
• autosomal dominant?

  • heterozygotes with one copy of mutated gene are affected
• autosomal recessive?

  • homozygotes with two copies of mutated gene are affected
• x linked?

  • males with one copy of mutated gene on x chromosome are affected
• karyotype - chromosomal analysis?

  • observe physical landmarks & bands to distinguish between chromosomes arranged in descending size order
  • represents cytogenetic characteristics of individual
  • to observe metaphase - need actively dividing cells
  • small b lymphocytes from blood samples
  • g banding technique - chromosome abnormality can be aneupolidy - involves trypsin digestion of chromosome & dna staining with giemsa
• fluorescence in situ hybridization (fish)?

  • analysis of chromosomes at dna/gene level of resolution
  • performed on metaphase & interphase cells
  • identifies numerical & structural abnormalities
• 3 types of fish probe?

  1. repetitive sequences - includes those at centromere of chromosome
  2. dna segments that will bind to & cover entire length of specific chromosome
  3. dna segments from specific genes/regions on chromosome that have previously been mapped/identified
• sanger chain termination sequencing?

  • uses synthesis of new dna strands that are complimentary to single stranded template
  • strand synthesis would normally proceed indefinitely until end of template is reached
  • but reaction mixture contains small percentage of dideoxynucleotides
• techniques for diagnostic testing for already known identity of mutation?

  • simple analytic methods - oligonucleotide ligation assay
• techniques for diagnostic testing for unknown identity of mutation?

  • discovery methods - dna sequencing/karyotyping