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)