Ch.6: Chromosomes and Cell Reproduction

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Ch.6 Chromosomes and Cell Reproduction

• Biology

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Cell Division/Cell Reproduction

• 2 Main Types of Cell Reproduction
• 1) Asexual-requires only one parent
• Ex Bacterial Cells reproduce by Binary
  fission- a) single circular DNA is copied, b)
  cell divides into 2 cells
• Each cell is identical to the other.
• 2) Sexual-requires two parents involving the
  union of 2 gametes (sex cells)

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• Eukaryotic cells form chromosomes before cell
  divisions.
• Gene-segment of DNA that codes for a protein or
  RNA molecule. Before the cell divides, DNA is
  copied and then begins to coil up into
  chromosomes.
• Chromosome-structure made up of DNA and proteins
• A chromosome is made up of 2 chromatids joined
  together by a centromere.

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Somatic Cells

• Somatic Cells-are all the cells in the body other
  than the gametes. They contain 23 pairs of
  different chromosomes or a total number of 46.
  Body cells have 2 sets of chromosomes, one set
  from each parent. They are diploid (2n). These
  chromosomes differ in size, shape, and the genes
  they carry.
• Each of the 23 pairs of chromosomes are made up
  of homologous chromosomes (which means they are
  similar in size, shape, and the genes they
  carry).

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Gametes

• Gametes-egg and sperm. They are haploid which
  means they have 1 set of chromosomes (n).
• When egg(n) and sperm(n) unite, they form 1 cell
  called a zygote (2n). A zygote is a fertilized
  egg cell. A zygote repeatedly divides by mitosis
  to form a complete organism.

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• Human somatic cells have 23 pairs of chromosomes.
  22 of the 23 pairs are called autosomes.
  Autosomes are chromosomes that are NOT involved
  in determining the sex of an individual.

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Sex Determination

• The 23rd pair (sex chromosomes) determine the sex
  of an individual.
• The 2 sex determining chromosomes X chromosome
  and Y chromosome.
• Egg and sperm carry 1 copy of each autosome and
  1 copy of sex chromosome.

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• The egg always carries an X chromosome.
• The sperm may carry an X or Y.
• Females XX
• Males XY
• It is the presence or absence of the Y
  chromosome that determines the sex of the
  individual.
• Karyotype-a picture of the chromosomes found in
  an individuals cells.

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• Cell Cycle repeating sequences of cellular
  growth and division during the life of an
  organism cell spends 90 of its time in the
  first 3 phases of the cell cycle which is
  collectively known as interphase.
• Interphase - a) First growth (G1)-cell grows
  carries out normal functions cell spends most
  time here cells not dividing stay here b)
  Synthesis (S)-DNA is copied c) Second Growth
  (G2)-cell prepares for division by assembling
  more membranes microtubules.
• Mitosis division of nucleus and chromosomes
  (Prophase, Metaphase, Anaphase, Telophase)
• Cytokinesis the process during which the
  cytoplasm divides and results in 2 cells.

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