Genetics and Cells

• Species 


  two organisms belong to the same species if they are able to produce fertile offspring
• Species must reproduce and pass on their advantageous alleles for survival of their species
• courtship behaviour is essential for successful mating and for species recognition. This helps a species to survive
• Courtship behaviour: a sequence of actions which is unique to each species. This is how animals identify members of their own species to reproduce with.
• Courtship rituals: sequence of dance moves, sounds, release of pheromones, display colourful feathers or fighting. Females observe the courtship ritual and decide if they want to mate with the male
• Importance of courtship: to ensure successful reproduction, enables them to to recognise own species and opposite sex, synchronises mating behaviour( indicates sexually mature and in season i.e releasing egg)
• Importance of courtship: to ensure survival of offspring because this forms a pair bond and increases likelihood of staying together and it also chooses a strong and healthy mate so an advantageous allele gets passed on
• Courtship rituals are genetically determined, so the more similar a species sequence is the more similar their DNA base sequence is
• Phylogenetic classification: arranges species into groups according to their evolutionary origins and relationships
• Phylogenetic classification tells us how closely related species are and how recent their shared common ancestors are
• Classification systems are an example of a hierarchy
• Hierarchy: smaller groups arranged within larger groups
• Binomial system(two names) : first name is genus and second name is species i.e homo sapiens
• Biodiversity can be measure by species diversity( species richness), genetic diversity and ecosystem diversity
• Biodiversisty can be used to describe a range of habitats from small local habitats to the earth
• A low biodiversity might not be a concern i.e a desert but if you have a decrease in biodiversity is a cause for cancer as this could be cause by human activity
• Farming techniques can reduce biodiversity so a balance must be found between conservation and farming
• Index of diversity: describes the relationship between the number of species in a community(species richness) and the number of individuals in each species(population)
• Genetic diversity within or between species can be made comparing the frequency of observable characteristics, the base sequence of DNA, the base sequence of mRNA and the amino acid sequence of proteins
• a gene is a shot section of DNA which codes for a polypeptide and functional RNA
• the location of a particular gene on a chromosome is called locus
• an allele is one of a number of alternative forms of a gene. Most genes occur in two, occasionally more different forms
• Chromosome: a threadlike structure of nucleic acids and protein found in the nucleus of most living cells, carrying genetic information in the form of genes.
• Humans have 23 pairs of chromosomes so 46 in total
• a homologous pair of chromosomes are exactly the same size, have exactly the same gene (identical genes) but might have different alleles
• chromosomes in eukaryotic cells are linear in shape
• To tightly coil the DNA to fit in the nucleus as chromosomes, the DNA is tightly wound around proteins called histones
• DNA wrapped around a histone is called a nucleosome
• Prokaryotes also carry DNA in chromosomes BUT the DNA molecules are shorter and circular. The DNA is not wound around histones instead it supercoils to fit the cell.
• There is also DNA found in chloroplasts and mitochondria. This DNA is similar to prokaryotic DNA in that it is shorter and circular.
• The genetic code is universal, degenerate and non overlapping
• The start codon is the first triplet of bases in a mRNA sequence that codes for a specific amino acid and it initiates translation
• At the end of every gene there are 3 bases that do not code for an amino acid and are known as the stop codon. These stop codons mark the end of the polypeptide chain and cause ribosomes to detach and therefor stop translation
• Each amino acid is coded for by more than one triplet of bases. This is what is meant by the genetic code to be degenerate
• Being degenerate is an advantage because if a point mutation occurs, even though the triplet of bases will be different, it may still code for the same amino acid and therefore have no effect
• Universal : The same triplet of bases codes for the same amino acid in all organisms this is why the genetic code is described as universal.
• Having a universal genetic code is an advantage as it means genetic engineering is possible e.g inserting the human gene for insulin into bacteria
• Non overlapping: each base in a gene is only part of one triplet of bases that codes for one amino acid. Therefore each codon or triplet of bases is read as a discrete unit.
• Non overlapping is and advance as if a point mutation occurs it will only affect one codon and therefore one amino acid
• Introns are sections of DNA that don not code for an amino acid and therefor a polypeptide chain. Introns are found in eukaryotic DNA but not in prokaryotic DNA. These get removed and splice out of mRNA molecules