Reproduction and Inheritance · 6 question types
Past paper frequency (2018 to 2024)
This topic accounts for approximately 17% of your exam marks.
Genetic crosses, Punnett squares, and dominant/recessive allele questions appear on almost every paper.
RNA (ribonucleic acid) is the messenger molecule that carries the instructions in a gene from the nucleus to the place where proteins are made. RNA is similar to DNA but with three important differences:
| Feature | DNA | RNA |
|---|---|---|
| Number of strands | Two (double helix) | One (single strand) |
| Sugar | Deoxyribose | Ribose |
| Bases used | A, T, G, C | A, U, G, C (uracil replaces thymine) |
| Length | Long (entire chromosomes) | Short (a copy of one gene) |
| Location | In the nucleus | Made in the nucleus, used in the cytoplasm |
In RNA, uracil (U) plays the role that thymine (T) plays in DNA, so the new pairing rules are:
There are several different types of RNA. The two most important for protein synthesis are: