Literary Physics

Syllabus dot point| Notes| * process information from secondary sources to describe an example of hybridisation within a species and explain the purpose of this hybridisation| Hybridisation – two genetically different strains of an organism are crossed to produce offspring with desirable characteristics. i. e. cross breeding cattle to produce better meat, which will benefit for human consumption Selective breeding of sheep to produce merino sheep which are hybrids produced by interbreeding other sheep varieties.Interbreeding other varieties of corn to produce the resultant hybrid corn that was hardy and produced large fruit. | * describe the process of DNA replication and explain its significance| * DNA double helix unwinds * DNA unzips * Nucleotides are added to each single strandDNA replication ensures that the genetic information is maintained. | * explain the relationship between proteins and polypeptides| A protein is made up of one or more polypeptides.A polypeptide is m ade up of a chain of many amino acids. | * analyse information from secondary sources to outline the evidence that led to Beadle and Tatum’s ‘one gene – one protein’ hypothesis and to explain why this was altered to the ‘one gene – one polypeptide’ hypothesis| Beadle and Tatum concluded that for each defective enzyme there was one gene on one specific area of a chromosome that had been mutated by irradiation. This led to their ‘one gene-one enzyme’ theory.The ‘one gene – one enzyme’ hypothesis changed to the ‘one gene – one protein’ hypothesis, once it was demonstrated that there are other proteins besides enzymes that are encoded by genes. Thomas Morgan's work led to a greater understanding of how genes are arranged on chromosomes and how genetic material can be exchanged (during crossing over) in meiosis. Morgan’s experiments showed without any doubt that: * the gene for eye colour in fruit flies is located on the X chromosome, and * hereditary factors can be exchanged between the X chromosomes of an individual.Morgan experimented with fruit flies (Drosophilia melanogaster) and determined that genes are carried on chromosomes. He used crossing over to determine locations of genes. He discovered that sex chromosomes look different to each other, and that eye colour gene in Drosophilia was located on the X chromosome, leading to the discovery of sex linkage. Boveri experimented with sea urchins and showed that a complete set of chromosomes was needed for normal development and that the NUCLEUS of a cell was concerned with inheritance.He postulated that each chromosome was different, chromosomes were transferred from one generation to the next during cell division, and that chromosomes must carry the many hereditary factors. Sutton – he observed during meiosis that chromosomes behaved randomly and gametes receive only one chromosome from each pair. | Distinguish between the terms gene and allele| A gene is a section of DNA that codes for proteins that expresses itself as the phenotype for example, two genes for eye colour. An allele is the alternative forms of a gene, i. e. for eye colour, B would code for blue while b for brown. |