Mitosis

1
Mitosis

• Cell division

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Chromosomes

• Rod shaped structures made of DNA and proteins
• Carry genetic material which is copied and passed
  on to generations of cells
• Always present, but not able to be seen because
  they are so thin

3
Chromosomes (cont)

• During most of their life they exist as
  chromatin, strands of DNA wrapped around protein.
• These proteins are called histones.
• Nonhistones control some DNA activities
• Each chromosome is a single DNA molecule

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Chromosomes (cont)

• Each half is a chromatid
• Formed when DNA copies itself before celldivision
• The constricted area of a chromatid is a
  centromere

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Chromosomes (cont)

• Each species has a specific number of chromosomes
  in each cell
• All chromosomes are either autosomes or sex
  chromosomes

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Sex chromosomes

• Determine the sex of an organism
• May carry other characteristics
• In humans
• Females XX
• Males XY
• 46 chromosomes
• Two sex chromosomes
• 44 autosomes

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Homologous chromosomes

• Each cell has two copies of each autosome, one
  from each parent. These are called homologous
  chromosomes
• Same size and shape
• Carry genes for same traits

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Karyotype

• A photomicrograph (fancy name for a picture taken
  by a microscope) of chromosomes of a dividing
  cell.
• Shows 23 pairs
• 22 pairs autosome
• One pair sex chromosomes

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Diploid cells

• Have two sets of chromosomes
• All normal cells are diploid
• Abbreviated as 2n
• Cells with both chromosomes for each homologous
  pair are called diploid cells

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Haploid cells

• Contain only one set of chromosomes
• Half the number of chromosomes of a diploid
• Only one chromosome of each homologous pair.
• Abbreviated 1n
• Sperm and egg cells are 1n

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Life cycle of a cell

• Two general periods in the life of a cell
• Interphase
• Mitosis

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Interphase

• Most of their life spent here
• Grows to mature size (G1)
• DNA is copied (S Phase)
• Time between DNA copy and cell division. Cell
  prepares for division(G2)
• Exit cell cycle, no changes or division made (G0)

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Mitosis

• A process of nuclear division followed by
  division of the cytoplasm.

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Types of cells

• Somatic cells body cells, all but sex cells,
  diploid
• Gametes - sperm and egg, sex cells, haploid
• Compare to autosomes and sex chromosomes

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Cytokinesis (page 151)

• Means division of cytoplasm of a cell
• In animal cells
• Cleavage furrow
• In plant cells
• Cell plate

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What is the end result of mitosis?

• Two identical cells just like the original cell.
• They are half the size the original cell
• They are called daughter cells