Question 5
Cystic fibrosis (CF) is a recessive gene disease meaning that a child has to inherit a defective CF gene from each parent. This means that there is a 25% chance of a child having cystic fibrosis if both parents are CF carriers Hence the number of children with CF (in a family whose parents are CF carriers) has a binomial distribution with n = the number of children in the family and p= 0.25
i. In a family of four (4) children whose parents are CF carriers, what is the probability that exactly one (1) of the children has cystic fibrosis. (2 mark)
ii. In a family of six (6) children whose parents are CF
carriers, what is the probability that one or more of the children
has cystic fibrosis.
i)
Sample size , n = 4
Probability of an event of interest, p = 0.25
P ( X = 1) = C (4,1) * 0.25^1 * ( 1 - 0.25)^3=
0.4219
...........
ii)
Sample size , n = 6
Probability of an event of interest, p = 0.25
X | P(X) |
0 | 0.1780 |
1 | 0.3560 |
2 | 0.2966 |
3 | 0.1318 |
4 | 0.0330 |
5 | 0.0044 |
6 | 0.0002 |
p(x>=1) = 1-p(0)
=1-0.178
=0.8220
................
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