Category: Genetic Variation and Information
In this unit, we start off with DNA and RNA as the genetic molecules from unit 1, this time identifying differences between prokaryotic and eukaryotic DNA, and chromosome structure. Extending from GCSE, we look at protein synthesis and the process of transcription. This is the use of RNA polymerase to make complementary pre-mRNA from a coding section of DNA. The pre-mRNA contains introns, which are then spliced out to form the shorter mRNA. Translation then occurs in the ribosome. Here, we meet a new clover shaped polynucleotide : transfer RNA. tRNA has anticodons on the bottom loop, complementary to the codons on the mRNA, and specific amino acids on the top. The ribosome has space for 3 tRNA.s to dock, and join together the amino acids to form a polypeptide.
Genetic variation can occur due to mutation or meiosis. A few simple mutations to the base sequence of DNA are discussed here ( there are more in Unit 8), along with independent segregation and ‘crossing over’ of chromatids in the first phases of meiosis. This genetic variation is then applied to Natural Selection. Students need to be able to differentiate between directional and stabilising selection.
Phylogenetic classification uses evolutionary origins as a way of grouping organisms into a hierarchy. The different organisms can be grouped by biochemical similarity . The most obvious of this is the sequence of DNA, which is obviously linked to the primary structure of key proteins.
In this unit, students are also expected to develop maths skills , including calculation of means and standard deviation, and understanding what standard deviation represents. Although, standard deviation will not be need to be calculated in the AQA exam.
