Control of cell replacement
• Density-dependent
inhibition
– Low amounts of
growth factor proteins
• Growth Factor
– Secreted by cells
stimulating division
• Enough cells, reaches
GF saturation,
inhibition
Cancer - Disease of the cell cycle
• Excessive division (out of control); tumor
– Benign; removed if pushing against vital organs
– Malignant; disrupts normal tissue & organ function
• Metastasis; spreads to other tissues via bloodstream & lymph
• Carcinoma
– Epithelial cells (e.g. skin,
intestinal lining)
• Sarcoma
– Connective or supportive
tissue
• (e.g. bone, cartilage,
muscles, fat, blood
vessels)
• Leukemia
– Blood or bone marrow;
specifically WBC’s
• Lymphoma
– Originates in lymphocytes
(immune cells)
Chromosomes, sex cells, and meiosis
• Somatic cells (typical
body cell) have 46
chromosomes, or 23
matched pairs
• Homologous chromosomes
or homologues
– Both have genes that code
for the same characteristics
– Will be at the same location
or locus
– e.g. if we think chromosomes
as sets of instructions or
manuals, we have two
versions, and loci would be
chapters
Why do we have two versions?
• We inherit one from each
parent
• of the 23 pairs in humans
– 22 pairs are autosomes
– 1 pair are sex
chromosomes
• XX females
• XY males
If we have two sets, than how do our
gametes only have one set?
• Tetrad = homologues come together, synapsis, (each with sister
chromatids)
• Crossing over = mixing or exchange of genes between homologues
• Note: no Interphase
– No duplication of chromosomes
Fertilization of sperm and egg produces variety of offspring
• 3 places for variation
– Tetrad formation and
crossing over
• Prophase I
– Independent assortment
• Depends on orientation of
chromosomes during
Metaphase I & II
– Random fertilization
• Preferably outside of
family
• Sites of crossing over
= chiasma
– Prophase I
Karyotype = inventory of chromosomes in mitotic metaphase
Karyotyping process
• centrifuge?
• Purpose / result of hypotonic solution?
• Digital arrangement of
chromosomes by size
& shape
• Stained and
compared
Meiotic abnormalities
• Trisomy 21
Down Syndrome
Cause?
Nondisjunction
chromosome
pair does not
seperate
Nondisjunction can also affect sex chromosomes
• XXY: male with some female characteristics and underdeveloped
sterile testes
• XO: female, typically sterile, shorter, decreased development
(treated with estrogen supplements)