6.4 - Issues of Cell Division on Human Health

Effects of Abnormal Mitosis (Cancer)

• Special control systems regulate the cell cycle at the $G_1$, $S$, $G_2$, and $M$ phases.
• Uncontrolled cell division causes continuous cell division and forms a tumour.

Uncontrolled Mitosis and Tumour Formation

• Benign tumour: Harmless and can be removed surgically.
• Malignant tumour: Cancer.

Causes of Cancer

• Factors that cause cancer:
  • Radiation: X-rays, gamma rays, and ultraviolet rays.
  • Chemicals: Tar in tobacco.
  • Carcinogens: Formaldehyde and benzene.
  • Genetic factors, bacteria, and viruses.
• Cancer cells spread and destroy surrounding normal cells, disrupting tissue function.
• Cancer cells spread through lymph vessels and blood vessels to other parts of the body, where new tumours form.
• Cancer that is not detected early causes organ damage and may eventually be fatal.

Effects of Abnormal Meiosis (Genetic Disorders)

Non-Disjunction

• Failure of spindle fibres during anaphase I or anaphase II prevents chromosomes from separating: non-disjunction.
• Gametes have abnormal chromosome numbers: 22 or 24 chromosomes.
• Fertilisation between a normal gamete (23 chromosomes) and an abnormal gamete (24 chromosomes) produces a zygote with 47 chromosomes.

Down Syndrome (Trisomy 21)

• An individual has 47 chromosomes, including an extra chromosome in chromosome set 21: trisomy 21.
• Characteristics: Stunted body growth, mental retardation, slanted eyes, and a slightly protruding tongue.