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Chromosomes

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Chromosomes PART 1 Honors Genetics Ms. Gaynor Why is Cell Division Important? Unicellular organisms Reproduce by cell division increasing the population. – PowerPoint PPT presentation

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Title: Chromosomes


1
Chromosomes
  • PART 1
  • Honors Genetics
  • Ms. Gaynor

2
Why is Cell Division Important?
  • Unicellular organisms
  • Reproduce by cell division ? increasing the
    population.

3
Why Do Multicellular Organisms Depend on Cell
Division?
  • Development Growth
  • Repair (ex tissue renewal)
  • Maintenance

4
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

5
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)

6
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)

7
Tightly coiled?
Not tightly coiled?
8
(No Transcript)
9
How Does DNA Fit into a Small Cell?
  • Prokaryotic organisms
  • No nucleus instead have a nucleiod region
  • DNA 1 chromosome

10
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

11
DNA histones ? form nucleosomes (help to
super coil DNA)
12
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.

13
The DNA molecules in a cellAre packaged into
chromosomes
14
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)
15
Chromosomes and Cell Division
  • In preparation for cell division (mitosis)
  • DNA is replicated (single ? double chromosome)
  • V shape ? X shape

16
Each duplicated chromosomehas two sister
chromatids, which separate during cell division
17
Double Chromosome Structure
Kinetochore attaches to spindle fibers
Sister
18
Another view
19
Draw and Label the Pieces of a Duplicated
Chromosome
20
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

21
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)

22
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

23
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.

24
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
25
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!
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