Please confirm topic selection

Are you sure you want to trigger topic in your Anconeus AI algorithm?

Please confirm action

You are done for today with this topic.

Would you like to start learning session with this topic items scheduled for future?

Updated: May 2 2017

Chromosomal Structure

  • Overview
    • Centromere
      • holds sister chromatids together
      • attachment of mitotic spindle fibers
        • allows chromosomes to be pulled to opposite poles during anaphase
      • variations in position
        • metacentric
          • centromere in the middle
        • submetacentric
          • centromere offset slightly towards one end
        • acrocentric
          • near complete displacement of centromere to one end
    • Nomenclature
      • long = q
      • short = p
        • remember: p = petite
      • translocation = t
      • deletion = del
  • Types of chromosomal alterations
    • Nondisjunction
      • homologous chromatids do not separate properly during meiosis
        • stage of nondisjunction affects gamete production outcome
          • nondisjunction in meiosis I results in 2 gametes with x 2 and 2 gametes x 0
          • nondisjunction in meiosis II results in 2 normal gametes, 1 gamete x 2 and 1 gamete x 0
        • zygote receiving 3 copies = trisomy
        • zygote receiving 1 copy = monosomy
      • risk greatly ↑ with ↑ in maternal age
        • more common in oogenesis than spermatogenesis
    • Translocation
      • exchange genetic info between nonhomologous chromosomes by breakage and repair
        • balanced
          • where exchanged fragment is still functional on another chromosome
        • unbalanced
          • where exchanged fragment cannot function properly
      • common in cancers
      • types
        • Robertsonian
          • balanced
          • always involve two acrocentric chromosomes
            • 13, 14, 15, 21, 22
          • results in loss of short arm and fusion of two long arms of different chromosomes
          • no clinical presentation because short arms of acrocentrics contain no vital info
            • is a translocation carrier
            • problems with gametogenesis and therefore reproduction
              • miscarriage, aneuploidy
              • depends on how chromosomes segregate during homologous pair separation
        • reciprocal
          • exchange of DNA between two non-homologous chromosomes
            • as long as no DNA is lost the phenotype is normal for that generation
              • is a translocation carrier
    • Inversion
      • type of rearrangement where part of chromosome is inverted in orientation
      • types
        • pericentric
          • inverted chromosomal segment includes centromere
          • remember: pericentric involves centromere
        • paracentric
          • inverted chromosomal segment does not include centromere
    • Ring chromosomes
      • causes
        • product of two breakage sites on the chromosome and the segment lost circularizes
        • ends of chromosomes join circularizing entire chromosome
      • usually lost during gametogenesis → monosomy
    • Isochromosome
      • replication of one arm of a chromosome with loss of the other
        • p-q → p-p'
      • lethal for autosomes
        • can be observed on sex chromosomes
    • Deletions
      • loss of chromosome segment
      • types
        • terminal
          • end of chromosome
        • interstitial
          • within the chromosome
Card
1 of 0
Question
1 of 1
Private Note