Chromosomes

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Chromosomes

• PART 1
• Honors Genetics
• Ms. Gaynor

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Why is Cell Division Important?

• Unicellular organisms
• Reproduce by cell division ? increasing the
  population.

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Why Do Multicellular Organisms Depend on Cell
Division?

• Development Growth
• Repair (ex tissue renewal)
• Maintenance

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Cell Division (Mitosis)

• Makes 2 genetically identical daughter cells from
  1 parent cell
• Before cells divide
• They duplicate their genetic material ? ensures
  that each daughter cell receives an exact copy of
  the genetic material, DNA

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Organization of the Genetic Material

• All of a cells DNA (genetic information) is
  called its genome
• In prokaryotes
• Genomesingle, long DNA molecule in a circle
• In eukaryotes
• Genome several DNA molecules grouped in clumps
  (called chromosomes)

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DNA Molecules

• DNA (in nucleus of eukaryotes) can be in 2 forms
• Chromatin DNA is not tightly packed together
  (loosely coiled)
• Occurs during interphase
• Chromosomes tightly packed together (TIGHTLY
  coiled)
• Occurs during mitosis (cell division)

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Tightly coiled?
Not tightly coiled?
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(No Transcript)
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How Does DNA Fit into a Small Cell?

• Prokaryotic organisms
• No nucleus instead have a nucleiod region
• DNA 1 chromosome

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How Does DNA Fit into a Small Cell?

• Eukaryotic organisms split their DNA into several
  pieces (called chromosomes)
• stored within the cell's nucleus
• DNA is coiled around proteins known as histones
• Uses nucleosomes to form a supercoil

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DNA histones ? form nucleosomes (help to
super coil DNA)
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Making Chromosomes

• Occurs right before cell division (mitosis)
• Steps
• DNA copies itself through DNA Replication
• The DNA coils (wraps) around proteins called
  histone proteins.
• Chromosomes are made.

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The DNA molecules in a cellAre packaged into
chromosomes
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Chromosome Structure

• Two shapes of chromosomes
• Single chromosome (1 copy of DNA) V shaped
• Double Chromosome (2 copies of DNA) X shaped
  a.k.a-duplicated chromosome

Occurs right before cell division (mitosis)
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Chromosomes and Cell Division

• In preparation for cell division (mitosis)
• DNA is replicated (single ? double chromosome)
• V shape ? X shape

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Each duplicated chromosomehas two sister
chromatids, which separate during cell division
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Double Chromosome Structure
Kinetochore attaches to spindle fibers
Sister
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Another view
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Draw and Label the Pieces of a Duplicated
Chromosome
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Chromosomes

• Every eukaryotic species has a characteristic,
  unique of chromosomes in EACH cell nucleus
• Ex Humans have 46 chromosomes
• of chromosomes does NOT necessarily equal
  complexity

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Different Types of Cells

• There are 2 types of cells in the human body
• Somatic cells all body cells
• 2. Gametes reproductive cells (sperm and egg)

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Different cell types ? different cell divisions

• Eukaryotic cell division consists of
• Mitosis, division of the nucleus
• Cytokinesis,division of cytoplasm
• Occurs in somatic cells
• In meiosis
• Gamete cells are produced after a reduction in
  chromosome number

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Chromosome Number

• Gametes (sperm/egg) have 1 copy of each
  chromosome and are called haploid.
• Somatic (body) human cells have 2 copies of each
  chromosomes and are called diploid.
• Human somatic cells have 23 PAIRS of chromosomes
  (total 46 chromosomes).
• All pairs of chromosomes differ in size, shapes,
  and set of genes.

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Haploid vs. Diploid

• Haploid when a cell has 1 copy of each
  chromosome.
• Expressed as n 23
• Diploid when a cell has 2 copy of each
  chromosome. (a.k.a TOTAL of Cs in organisms)
• Expressed as 2n 46

Haploid sperm cell
n
Haploid egg cell
n
Fertilization
2n
Diploid Zygote cell
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Set of Chromosomes

• Each chromosome set contain 2 homologues.
• Chromosomes have a twin or matching pair.
• Homologous Chromosomes chromosomes that are
  similar in shape, size, and genes.
• Each homologue in a pair comes from each parent!