(i)  State the technique used to collect cells for pre-natal testing.                  

(ii) State the method used to arrange the chromosomes in a karyotype.        

(iii) State at what stage in the cell cycle the cells would be when this photograph was taken.  

Albinism is inherited as a recessive trait; the alleles of the gene involved are A and a. An individual with albinism produces little or no pigment in the eyes, skin and hair. In a family, one sister has albinism while the parents and other sister have
normal pigmentation.

(i) Determine, using a Punnett grid to show your reasoning, the possible genotypes of the sister with normal pigmentation. 

(ii) Deduce the probability that the next child of this couple will have albinism.  

(i) amniocentesis/sampling amniotic liquid/fluid (via needle)/chorionic villus sampling
(ii) chromosomes are grouped by pairs according to size and structure/band pattern/location of centromeres
(iii) metaphase/late prophase of mitosis

(i) Punnett grid shows the gametes (A and a) on one axis and the gametes (A and a) on the other axis and genotypes (AA, Aa, Aa, and aa) of offspring;
AA/homozygous dominant and Aa/heterozygous (show normal
pigmentation); Both needed 
Do not award marks to any answer suggesting sex linkage.
(ii) 1/4 /25 %/0.25 probability of albinism / 1 in 4 chance

(i) A broad range of inaccurate answers were given, e.g. karyotyping, polymerase chain reaction, or just no response at all.

(ii) This question proved to be difficult because three components (pairs, size, structure/banding) were needed for the one mark. Many candidates forgot that chromosomes are placed in pairs in a karyotype. Some just mentioned ‘karyotyping’. In this case, candidates should realize that just repeating a term (karyotyping) from the question stem will not get them credit.

(iii) Few mentioned metaphase; interphase, which was commonly given, lost the mark. Several answers suggested meiosis.

i) A Punnett grid usually given with correct genotypes and correct genotypes of sister with normal pigmentation. Confused answers gave pedigree charts or introduced sex linkage.

ii) Often the correct percentage or ratio was given. In some cases, this occurred despite an incorrect Punnett grid in (i).