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Chromosome Disorders

  • Mistakes during meiosis
  • Both chromosome copies in sperm or egg
  • Piece of chromosome lost
  • Usually results in non-viable zygote

Comments

Chromosomal disorders result from mistakes made during meiotic chromosomal replication. There are a number of different mistakes that can be made. Most, but not all, are fatal. Both copies of a chromosome, for example, could end up in a sperm or egg if they were not pulled apart during the final stages of meiosis. Or, an entire or just a piece of a chromosome could be lost.

Down Syndrome, for example, usually is caused by an extra chromosome 21 (that is, both copies of chromosome 21 were included in either the sperm or the egg, so that when the sperm and egg combine there genetic material there is an extra chromosome).