Human Chromosomes

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Human Chromosomes
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• The picture below shows the chromosomes from a
  normal male as viewed through a microscope.

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• To assist analysis, the complete set of
  chromosome images is organised according to an
  international convention to for a karyotype.

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Shorthand

• The shorthand way of denoting the pairs of
  chromosomes for each sex is as follows-
• A normal male 46XY
• A normal female 46XX
• The 22 matched pairs of chromosomes in both male
  and females are termed autosomes.

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• The different autosomes can be distinguished by
• Their size
• The position of their centromere. Chromosomes
  that have their centromere centrally positioned
  are called metacentric. Submetacentric
  chromosomes have the centromere towards one end
  and acrocentric chromosomes centromeres are very
  close to one end.
• The patters of light and dark bands that result
  from special staining techniques.

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Autosomes are identifies by the numbers 1 to 22
in order of decreasing size number 1 chromosomes
are the longest.
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Wrong numbers and other errors

• Various changes can occur involving chromosomes
  including
• Changes in the total number of chromosomes
• Changes involving one part of a chromosome
• Changed arrangements of chromosomes

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Changes in the total number of chromosomes

• Babies with additional or too few chromosomes
  rarely carry to term. The exceptions are

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Changes involving one part of a chromosome

• Duplication in which part of a chromosome is
  duplicated.
• Deletion in which part of a chromosome is
  missing.

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Changed arrangements of chromosomes

• Structural changes may occur in which the
  location of a chromosome segment is altered so
  that it becomes located to a new region within
  the karyotype. Such a change is known as a
  translocation.

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Chromosomes and sex determination.