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Cell Reproduction
Cell Division
All cells are derived from preexisting cells
New cells are produced for
growth and to replace damaged
or old cells
Differs in prokaryotes (bacteria)
and eukaryotes (protists, fungi,
plants, & animals)
Keeping Cells Identical
The instructions for
making cell parts
are encoded in the
DNA, so each new
cell must get a
complete set of the
DNA molecules
DNA Replication
DNA must be
copied or
replicated
before cell
division
Each new cell
will then have
an identical
copy of the
DNA
Original DNA
strand
Two new,
identical DNA
strands
Identical Daughter Cells
Two
identical
daughter
cells
Parent Cell
Chromosomes
Chromosome Structure
• The structure of chromosomes in
eukaryotic cells and prokaryotic cells is
different.
Recalling Eukaryotes and
Prokaryotes
• What is a eukaryotic cell?
• A “true nucleus”
• Membrane bound organelles
• Found in multicellular organisms
Recalling Eukaryotes and
Prokaryotes
• What is a prokaryote?
• No membrane bound nucleus.
• Lacks the presence of a nucleus.
• Unicellular organisms: bacteria
Eukaryotic Chromosomes
 Each chromosome is composed of a single,
tightly coiled DNA molecule
 Chromosomes can’t be seen when cells aren’t
dividing and are called chromatin
Eukaryotic Cell Chromosome
• Rod shaped structures.
• DNA is tightly coiled and compacted.
• Consists of a single DNA molecule
wrapped around proteins called
histones.
• Proteins involved in controlling
activities of specific regions in the DNA
are nonhistone proteins.
Compacting DNA into
Chromosomes
DNA is
tightly
coiled
around
proteins
called
histones
Eukaryotic Chromosomes
All eukaryotic cells store genetic
information in chromosomes
 Most eukaryotes have between 10 and 50
chromosomes in their body cells
 Human body cells have 46 chromosomes or 23
identical pairs
Chromosomes
• Consist of two identical
halves(Chromatid).
• Chromatids are formed as the DNA
makes a copy of itself before division.
• Chromatids are joined together at the
centromere.
• The centromere holds the
chromosomes together until division.
Chromosomes in Dividing
Cells
Duplicated
chromosomes
are called
chromatids & are
held together by
the centromere
Called Sister Chromatids
Chromosomes
• Between cell
division, DNA is not
tightly coiled in
order to be easily
read.
• The loose coils are
called chromatin.
Prokaryotic Chromosomes
• Much simpler than eukaryotic
chromosomes.
• Most cell consist of only 1
chromosome attached to the inside of
the cell membrane.
• Circular shape
Prokaryotic Chromosome
The DNA of
prokaryotes
(bacteria) is one,
circular
chromosome
attached to the
inside of the cell
membrane
Chromosome Numbers
• Each species has a characteristic
number of chromosomes in each cell.
• In humans, this number is 46.
• In potatoes, plums, and chimpanzees
the number is 48.
Autosomes vs Sex
Chromosomes
• Sex chromosomes are chromosomes
that determine the sex of an organism
and may also carry additional genes.
• In humans, sex chromosomes are
either x or y.
• Females have 2 X chromosomes while
males have an X and a Y.
Autosomes vs Sex
Chromosomes
• The remaining chromosomes are called
autosomes.
• Humans have 44 autosomes and 2 sex
chromosomes.
Chromosomes
• Every cell of an organism produced by
sexual reproduction has 2 copies of
each autosome.
• One copy of each autosome from each
parent.
• The two copies are called homologous
pairs.
• Each chromosome in the pair contains
genes for a specific trait.
Karyotype
A picture of the
chromosomes from
a human cell
arranged in pairs by
size
First 22 pairs are
called autosomes
Last pair are the sex
chromosomes
XX female or XY
male
Boy or Girl?
The Y Chromosome Decides
Y - Chromosome
X - Chromosome
Diploid and Haploid Cells
• Cells having two sets of chromosomes
are called diploid.
• Cells having one set of chromosomes
are called haploid.
Diploid Cells
• Diploid cells have both chromosomes
for each homologous pair.
• They have 2 sex chromosomes in
humans and many others with sex
chromosomes.
• All normal cells (except reproductive
cells) are diploid.
• The diploid number is commonly
abbreviated as 2n.(in humans n=23)
Haploid Cells
• Human sperm cells and egg cells are
called haploid cells (or 1n).
• Cells that contain only one set of
chromosomes.
• When a sperm cell (1n) and an egg cell
(1n) combine to create the first cell of a
new organism, the new cell will be
diploid(2n).