RI 2023 Nov P3 answers

2023 Nov P3 answers Question 1 Mitosis is a key process in the development of a fertlised egg into an adult human. Each mitotic cell division is preceded by DNA replication. (a) (i) Explain the significance of mitosis in the development of a fertilised egg into an adult human. [3] 1. mitosis results in increase in number of cells which is essential for biological processes like tissue growth in a multicellular organism; 2. and replacement of cells for tissue repair; 3. mitosis produces 2 genetically identical diploid daughter nuclei, each of which has the same number and same type of chromosomes (2 sets/homologous chromosomes) thereby contributing to genetic stability in all cells of the adult human; (ii) Name one environmental factor and one lifestyle factor that are associated with increasing the risk of mutations that lead to cancer. [2] environmental factor: exposure to ultraviolet light / ionising radiation / radioactivity lifestyle factor: smoking and exposure to carcinogens such as tar in cigarette smoke (iii) Explain how random errors that occur during the process of DNA replication can result in different types of changes to DNA sequences. [4] 1. Mistakes can occur during the synthesis of new daughter strand catalysed by DNA polymerase*, during DNA replication; OR Mistakes made during DNA replication could have escaped proofreading by DNA polymerase during DNA replication, A: DNA repair enzymes also not correct the mistake. 2. Substitution* mutation where a nucleotide/base is replaced by a different nucleotide; 3. Inversion* – a segment of nucleotide sequences separates from the allele and rejoins at the original position but it is inverted; 4. The length of DNA is unchanged but the sequence will be different; 5. Insertion /addition* – occurs when one or several nucleotides are inserted in a sequence 6. Deletion* – occurs when one or several nucleotides are removed from a sequence of base(s) 7. Resulting in a change in both length and sequence of the DNA; Pt 4 with 2 or 3; Pt 7 with 5 or 6 Must have point 4 or 7 to get full marks.

(iv) Suggest why it is important for doctors to be able to distinguish passenger mutations from driver mutations. [2] 1. passenger mutations do not result any change in the function of the cell and hence are not linked to the development of cancer so doctors will not need to prescribe drugs; 2. driver mutations result in the benign tumour formation and subsequently invasive cancer resulting in uncontrolled cell division and cancer development; 3. Doctors need to distinguish the two in order to make an accurate diagnosis/ suggest appropriate treatment if driver mutations are discovered in patients; (v) State the name given to the type of mutation in cancer development that results in a dominant driver mutation. [1] Gain-in-function mutation* (vi) State the name given to the type of gene that, when mutated, contributes to cancer devel