Prof Duncan Shaw

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Lecture 38

• Prof Duncan Shaw

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Chromosomes and karyotypes

• Chromosomes are easily prepared from blood (and
  other) cells, and examined by microscope - a
  karyotype
• Normal human body cells (somatic cells) are
  DIPLOID 23 pairs of chromosomes
• Numbers 1-22 (autosomes)
• X and Y (sex chromosomes)
• XX in females, XY in males
• Germ cells (egg, sperm) have 23 chromosomes -
  HAPLOID

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p (short arm) petit
q (long arm)
P arms of acrocentrics (13,14,15,21,22) have
repeated ribosomal RNA genes
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Mitosis

• Process of cell division in somatic cells
• 1 diploid cell 2 diploid cells
• Goes through several defined stages
• Chromosomes are passed on as exact copies without
  recombination (usually)
• Segregation is the process whereby one copy of
  each replicated chromosome goes to each daughter
  cell

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Meiosis

• Process of cell division in germ cells, to
  produce eggs or sperm (gametes)
• Diploid cell haploid cells
• Goes through several defined stages
• Chromosomes are passed on as re-arranged copies
  due to recombination - creates genetic diversity

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Oogenesis spermatogenesis

• Oogenesis is the process of egg formation
• Spermatogenesis is the process of sperm formation
• Both go through several stages, with different
  timing in males than females
• Sperms go through more cell divisions than eggs
  do - more chance of mutation

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Fertilisation

• 2 haploid cells (egg, sperm) form 1 diploid cell
  (the zygote) which develops into the embryo
• Whether sperm contained an X or Y chromosome
  determines if embryo is female or male
• Embryo contains an assortment of genes from each
  original parent - more genetic diversity
• Mitochondria (and their DNA) come only from
  mother via the egg - maternal inheritance