14) i) 3, 4, 5 ii) E
i) 7 has inherited the disease in an autosomal recessive fashion since 4 and 5 do not have the disease. Therefore, 4 and 5 must be heterozygous.
Since 7 is affected, 3 must also be heterozygous.
ii) We now know that 3 and 4 are heterozygous.
T TT Tt
t Tt tt
The only way for a person to be affected by a person is if they are homozygous and only have the recessive alleles i.e. ‘tt’
Therefore, the probability of the child being affected by the condition is 1/4.
Probability of a having a girl child = 1/2
Probability of having a girl with disease = 1/2 x 1/4 = 1/8