1 For example, the disorder sickle cell anaemia is caused by a mutation in the gene that instructs the building of a protein called haemoglobin. 2  This causes the red blood cells to become an abnormal, rigid, sickle shape. 3  However, in African populations, having this mutation also protects against malaria.
Optimistic time - generally the shortest time in which the activity can be completed. It is common practice to specify optimistic times to be three standard deviations from the mean so that there is approximately a 1% chance that the activity will be completed within the optimistic time.
Physical activity is defined by its duration, intensity, and frequency ï® Duration is the amount of time spent participating in a physical activity session ï® Intensity is the rate of energy expenditure ï® Frequency is the number of physical activity sessions during a specific time period (e.g. one week).