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Standards
2a. Know meiosis is an early step in sexual reproduction in
which the pairs of chromosomes separate & segregate
randomly during cell division to produce gametes
containing 1 chromosome each.
2b. Know only diploid cells, spermatogonia & oogonia
undergo meiosis.
2c. Know random chromosomal segregation explains the
probablitity that a particular allele will be in a gamete.
2d. Know new combos of alleles are generated in a zygote
through the fusion of male & female gametes
(fertilization).
2e. Know why half an person’s DNA sequence comes from
each parent.
2f. Know the role of chromosomes in determining a
person’s sex.
Cell Cycle
Chromosomes
Compact, coiled DNA
Chromatid

One half of the
chromosome
Centromere


Between the two
chromatids
holds them together
Number of Chromosomes
Humans have 46 chromosomes
2 are sex chromosomes
44 are autosomes
Types of chromosomes
Sex chromosomes


Chromosomes that
determine the sex of
an organism
Humans have an X or
Y chromosome
Autosomes

All other
chromosomes in an
organism
Homologous Chromosomes
There are only 23 different
chromosomes
To have 46 we have two
copies of each chromosome


We get one from our mom
and one from our dad
The pairs of each
chromosome are called
homologues
Homologues carry genes
for the same traits
Karyotype
Show’s the 23 pairs of
chromosomes
22 homologous pairs
of autosomes
Diploid & Haploid
Diploid


Cells that have 2 sets
of chromosomes
All cells, other than
reproductive cells, are
diploid
Haploid


Cells that have only 1
set of chromosomes
Reproductive cells
(sperm & eggs) are
haploid
Cell Division
All cells come from
preexisting cells
Prokaryotes

Binary Fission
Eukaryotes


Mitosis
Meiosis
Binary Fission
The chromosome makes
a copy of itself
The cell grows until it
reaches about 2x it’s size
A cell wall forms between
the two chromosomes
and the cell splits
Mitosis
How all cells divide
EXCEPT reproductive
cells
The cytoplasm and
nucleus both divide
Results in two cells
that are genetically
identical
Mitosis – Cell Cycle
Interphase


Time between cell
divisions
3 phases
Cell Division


Time when the cell is
dividing
2 phases
INTERPHASE
G1 phase


Grow to mature size
Gap between cell
division & DNA
replication
S phase

DNA is copied
G2 phase


Prepares for cell division
Gap between DNA
replication & cell division
Mitosis - Prophase
DNA is shortened and
tightened into chromosomes
Nucleolus & nuclear
membrane break down &
disappear
Two centrosomes appear



Animals also have centrioles
Centrosomes move to oppositie
poles of cell
Spindle fibers radiate from
centrosomes
Mitosis - Metaphase
Spindle fibers move
chromosomes to the
center of cell
Mitosis - Anaphase
Chromatids separate
at the centromere and
are pulled to opposite
poles of cell by
spindle fibers
Mitosis - Telophase
Spindle fibers break down
Chromosome loosens up
Nuclear envelope forms
around each set of
chromosomes
Nucleolus forms
Cytokinesis
Cell membrane
pinches inward
creating a cleavage
furrow
Eventually leads to
two cells
Cell Plate
Only in plants
Golgi forms vesicles that fuse at the midline and divide
the cell
Makes a cell wall