(a)
(i) Gregor Mendel.

(ii) Law of Segregation: Characteristics are governed by a pair of factors (genes). These factors separate at gamete formation and each gamete receives only one of the pair. At fertilisation a pair of factors is reestablished for each characteristic.

(b)
(i) Gene: A short section of DNA that holds the code for a particular protein.

Recessive: The allele that is only expressed when two copies are present. It is prevented from being expressed by the dominant allele. (Example: t)

(ii) Gene mutations may be caused by X rays or UV rays, or cigarette smoke.

(iii) Mutation type: Chromosomal

Condition: Down’s syndrome

(iv) For this to be possible, both parents must be carriers, i.e., heterozygous for haemochromatosis, as shown in the cross below.

(v) Genetic screening could be used to determine the child’s genotype.

Using DNA profiling techniques, a radioactive probe is introduced to a sample of the DNA. If a normal gene is present the probe sticks to it and can be seen. If no probe is seen the gene is mutated. The child is a carrier if they have one mutated gene.

(c)
(i) X-linked or sex-linked

(ii)

(iii)

(iv) Person 7 has two dominant genes (NN). Therefore, she will give one of these, (N) to any child she has. Even if her partner gives a mutated gene, (n) to their child, the child will be a carrier (Nn) but will not have the condition.