Genetic information, variation and relationships between organisms

DNA, genes and chromosomes

c   Eukaryotic cells have chromosomes of linear DNA associated with histones. 

c   Prokaryotic cells contain short, circular DNA that is not associated with histones.

c   Mitochondria and chloroplasts contain DNA like that of prokaryotes.

c   Genes as regions of DNA, occupying a fixed locus, coding for the amino acid sequence of a polypeptide or a functional RNA

c   DNA is a triplet code which is universal, non-overlapping and degenerate.

c   Much of eukaryotic DNA does not code for polypeptides. There are non-coding regions of multiple base repeats between genes. There are also introns within genes which separate coding sequences (exons).

Protein synthesis

c   The concept of the genome and the proteome.

c   The structure of molecules of mRNA

c   The process of transcription in prokaryotes to produce mRNA.

c   The process of transcription in eukaryotes to produce pre-mRNA which is subsequently spliced.

c   The process of translation.

c   The roles of ribosomes, tRNA and ATP.

c   The structure of molecules of tRNA.

c   The structure of molecules of tRNA.

c   Gene mutations arise spontaneously during DNA replication and include base deletion and base substitution.

c   The degeneracy of the genetic code means that not all base substitutions cause a change in the amino acid sequence.

c   Mutagenic agents can increase the risk of gene mutation.

Meiosis

c   Meiosis produces daughter cells produces genetically unique daughter cells. 

c   The process of meiosis involves two nuclear divisions and forms four haploid daughter cells.

c   Independent segregation and crossing over result in genetically different daughter cells.

c   Mutations in the number of chromosomes can arise spontaneously by chromosome non-disjunction during meiosis.

Genetic diversity and adaptation

c   The concept of genetic diversity.

c   The principles of natural selection in the evolution of populations (including random mutation, reproductive success, inheritance of the beneficial allele and increasing allele frequency in the next generation).

c   Natural selection results in species that are better adapted to their environment. This included anatomical, physiological or behavioural adaptations.

c   Directional selection, exemplified by antibiotic resistance in bacteria, and stabilising selection, exemplified by human birth weights.

c   Required practical 6: Use of aseptic techniques to investigate the effect of anti-microbial substances on microbial growth

Species and taxonomy

c   The concept of a species.

c   Courtship behaviour as a necessary precursor to successful mating. 

c   The role of courtship in species recognition.

c   Phylogenetic classification is based on evolutionary origins and relationships.

c   The hierarchical nature of classification into taxonomic ranks.

c   The binomial identification of species based on its genes and species.

c   Advances in immunology and genome sequencing help to clarify evolutionary relationships between organisms.

c   Genetic diversity within, or between species, can be made by comparing the frequency of characteristics, the base sequences of DNA or mRNA, or the amino acid sequences of proteins.

Biodiversity within a community

c   The concepts of biodiversity, species richness and index of diversity.

c   Calculation of the index of diversity (d).

c   Farming techniques reduce biodiversity. The balance between conservation and farming.

c   Quantitative investigations of variation within a species involve:

• collecting data from random samples
• calculating a mean value of the collected data and the standard deviation of that mean
• interpreting mean values and their standard deviations