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.
When first activity completes, if there is then a delay or wait period before the second activity starts, this is called lag and the delay is known as the Lag Time. Lag Time is the delay between the first and second activity. For example, the time duration for the first activity is 3 days, and for the second activity it is 2 days. After completing the first activity you wait for one day, and then you start second activity.