Genes have a role in determining the overall phenotype of an organism.

Mark scheme

Marking points from the official mark scheme (May/June 2024). The mark or mark type is shown in brackets.

1. [5] (a) any five from:
2. [5] (a) 1 a gene codes for a protein which determines the phenotype ;
3. [5] (a) 2 F8 gene ;
4. [5] (a) 3 located on X chromosome / sex-linked ;
5. [5] (a) 4 ref. to recessive allele ;
6. [5] (a) 5 non-functioning factor VIII (protein) or less factor VIII (protein) or no factor VIII (protein) ;
7. [5] (a) 6 (so) blood does not clot quickly enough / excessive bleeding occurs (after an injury) ;
8. [5] (a) 7 link the phenotype to the genotype ; e.g. XF XF = normal female XF Xr = normal female Xr Xr = affected female XF Y = normal male Xr Y = affected male
9. [5] (a) 8 AVP; e.g. prevents activation of thrombin / fibrinogen not converted to fibrin / ref. to mostly males affected / different mutations cause a range of severity of haemophilia
10. [3] (b) any three from:
11. [3] (b) 1 lele is, homozygous recessive / two recessive alleles ;
12. [3] (b) 2 le (allele) / lele, codes for a non-functional enzyme ;
13. [3] (b) 3 no, active gibberellin / GA1 or ref. to gibberellin inactive ;
14. [3] (b) 4 no/less, cell elongation or no/less, stem elongation / increase in internodal length ;
15. [3] (b) 5 AVP; e.g. ref. to GA 3ß-hydroxylase / GA3-oxidase / last enzyme in the pathway that produces, active gibberellin / GA1 le allele codes for alanine instead of threonine (in the enzyme)
16. [3] (c) any three from:
17. [3] (c) 1 (DELLA proteins) bind to, PIF / transcription factor ;
18. [3] (c) 2 PIF / transcription factor, cannot bind to, DNA / promoter ;
19. [3] (c) 3 RNA polymerase cannot bind to promoter ;
20. [3] (c) 4 no transcription / mRNA not made ;