Mitosis
Cell division for growth & repair
Somatic Cell (parent cell)
2 identical
Meiosis
Cell Division for Reproduction
Cancer – uncontrolled cell division
Normal Cell
• Anchorage dependence • Contact inhibition
• Checkpoints observed • Tumor suppressor &
proto-oncogenes functioning properly • Set life span (# of
divisions) - apoptosis
Cancer Cell
• Can metastasize
• Invades surrounding tissue
• Angiogenesis
• Ignores checkpoints • Mutations in tumor
suppressor & proto-oncogenes (become oncogenes)
DNA Replication
What Cellular Structure Holds
the Genetic Information?
• Chromosomes
– Condensed, distinct form of genetic material
• Chromatin
– Is the chromosomal material in its
Mitosis –
produces 2 diploid cells
The “getting ready”
stage for cell division is called Interphase
•DNA replicates
•Organelles increase in number
•Cell grows in size
Prophase
• Start of mitosis
• Chromatin condenses into rod-like
chromosomes
– Each chromosome consists of sister
chromatids, connected at the centromere
Metaphase
• Chromosomes align themselves in flat
Anaphase
• Centromeres split. • Sister
Telophase
• Chromosomes
unravel, returning the chromatin to its non-dividing threadlike state.
Cytokinesis
• Division of the cytoplasm.
Cytokinesis
• Differs in animals and plant cells.
• Plant cells form a cell plate.
– membranous vesicles congregate at center of cell.
Cytokinesis
• Animal cells form a
cleavage furrow. – Forms around the
periphery of the dividing cell.
– Furrow becomes deeper and deeper until membrane
Chromosomes Come in Matched
Pairs
• Homologous pairs: chromosomes that are closely matched in size and shape
– Determine the same traits
• Sex chromosomes: Those that determine the gender of the
Chromosomal Theory of
Inheritance
• The two members of
each pair of a
homologous pair of chromosomes carry alleles for the same genes and, therefore, affect the same traits.
Mapping genes
• Locus: location of a gene on a
chromosome.
• Currently trying to
map all human genes to the appropriate
chromosome. • Example: gene
Sexual reproduction
• Type of reproduction in which genetic
information from
female combines with male.
• Requires fertilization
– Fusion of gametes (egg and sperm)
Meiosis
• Produces haploid cells (gametes-eggs and sperm)
– Posses only one member of each pair of homologous chromosomes
• Chromosomes replicate before meiosis (during Interphase)
Prophase I
• Chromatin condenses into compact
chromosomes.
• Nuclear envelope disappears.
• Synapsis occurs.
– Homologous pairs of
chromosomes closely align allowing exchange of
Metaphase I
• Aligned pairs of replicated
Anaphase I
• Members of
homologous pairs of chromosomes
separate from each other
• They move to opposite poles of the cell.
– Chromosomes
Telophase I
• Chromosomes cluster at opposite poles of cell and begin to decondense
• Nuclear envelope may reform.
• Cytokinesis occurs • Interkinesis: phase
between meiosis I and and II.
Prophase II
• Partially unraveled chromosomes
Metaphase II
• Chromosomes move to cell equator.
• No longer
homologous pairs, so chromosomes line up singly in middle of
Anaphase II
• Centromeres divide and chromosomes separate.
Telophase II
• Clustered
chromosomes at cell pole begin to
decondense.
• Nuclear membrane develops.
• Cytokinesis occurs. • Produces four
Cell Cycle
• Repetitive sequence of events that
characterizes life of cell.
• Consists of two main phases:
– Interphase
• Period that cells are in when not dividing. • 90% of cell cycle
– M phase
Cell Cycle
• Interphase has three subphases
– G1 (first gap)
• Cell makes copies of organelles and grows larger
– S (synthesis)
• Genetic material is copied
• End of this phase, cells chromosomes are doubled
– Copies are attached; thus total number of chromosomes remains the same
– G2 (second gap)
Regulation of Cell Cycle
• Cell cycle must be regulated or can result
in
cancer
– Uncontrolled cell growth
• Metastasize: cell breaks free from original
Regulation of Cell Cycle
• Two checkpoints
– First between G1 and S – Second between G2 and M
• To pass checkpoints, cell must possess appropriate amount of protein in
cytoplasm.
Regulation of Cell Cycle
• To pass checkpoints, cell must possess
appropriate amount of regulating protein in
cytoplasm.
– When regulator concentration is high, cell cycle progresses.
– When low, cell cycle is suspended at that stage.
• External and internal regulatory agents
also influence passage through
Why So Some Genetic Traits Tend
to Travel Together?
• Chromosomes contain genes
– Chromosomes follow law of independent assortment, not genes
• If two genes are on the same
chromosome,
Chromosomes Can Exchange
Segments During Meiosis
• Crossing over
– Exchange of genetic material between
chromatids of homologous chromosomes. – Occurs at the
Chromosomes Can Exchange
Segments During Meiosis
• Crossing over
– Important mechanism for creating new
combinations of genes.
