chromosome landmarks:

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chromosome landmarks 1) size --- length of
DNA sequence is proportional to the number of
genes 2) centromere position 3)
location of nucleolar organizers 4)
heterochromatin patterns 5) other banding
patterns (due to staining, e.g., Giemsa) 6)
telomeres
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Progressive levels of chromosome packaging
- nucleosomes - histone octamer (H2A, H2B, H3,
H4) - DNA helix - solenoid coiled
nucleosome chain - stabilized by H1 histone
- scaffolding solenoid loops attach to
nonhistone protein - supercoiling of
scaffold and solenoid loops
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mitosis occurs in somatic cells process by
which a cell produces two exact replicas of
itself

• chromosome duplication/DNA replication
• 2) sorting of replicated chromosomes
• 3) nucleus cell division

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meiosis occurs in gonads process by which
genome is halved to produce haploid gametes

• chromosome duplication/DNA replication
• 2) pairing of replicated homologous chromosomes
• 3) genetic crossover exchange between
• homologous chromosomes
• 4) separation of homologous pairs during the
  first meiotic
• division (centromeres do not divide)
• 5) sorting of replicated chromosomes
• 6) nucleus cell division

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Take home points chromosomes are composed
of DNA and histones the nucleosome is the
fundamental unit of chromosome structure, consist
ing of DNA wrapped around a histone octamer
several kinds of higher order coiling are
required for the highly condensed chromosomes
observed in mitotic and meiotic metaphase
haploid number (n) represents the number of
different kinds of chromosomes diploid (2n) is
the total number homologous chromsomes
contain the same genes in the same
order homologs can be identified by shared
features in mitosis, a diploid cell
undergoes one round of DNA replication and
nuclear division, resulting in two genetically
identical products
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in meiosis, a diploid cell undergoes one round of
DNA replication and two nuclear divisions,
resulting in four genetically unique haploid
cells (gametes) meiosis differs from mitosis in
that - homologous chromosomes pair - homologs
undergo recombination - during the first cell
division, the paired homologs separate to
opposite poles of the cell