Describe how a harmful mutation on DNA may lead to sickle cell anaemia and how useful mutations contribute to natural selection and hence evolution FACTS: 17 SYNTHESIS: 3 Sickle cell anaemia is caused by a mutant allele on chromosome number 11 The mutant allele is responsible for the production of haemoglobin S instead of haemoglobin A Haemoglobin S causes the red blood cells to become sickle shaped The sickle shaped celled block the small blood vessels and they carry a limited amount of oxygen The genotypes or genetic codes of individuals (even from the same family) are different form each other because: o The gametes produced by meiosis are different from each other o There is chance fertilization of egg cells by sperm cells o Mutations also results in new genotypes as we move from one generation to the next All three of the above ensure that the offspring of the same species show a great deal of variation Only those individuals that have characteristics that are favourable to enable it to compete successfully for resources in the environment and protect it from other organisms in the environment are able to survive These organisms reproduce to form offspring who also have the favourable characteristics Organisms that do not possess these favourable (advantageous) characteristics will die Charles Darwin called this Natural Selection, implying that Nature selected only those that were the best adapted to the environment to live and reproduce As Natural Selection occurs from generation to generation, there is a continual, gradual change in populations Sometimes the populations that results are so different for the earlier populations that they cannot reproduce any more This leads to SPECIATION (the evolution of new species) FACTS: 17 Marks Description 3 Well structured – demonstrate insight and understanding of question 2 Minor gaps or irrelevant information in the logic and flow of the answers 1 Attempted but with significant gaps and irrelevant information in the logic and flow of the answers 0 Not attempted/nothing written other than question number/no correct information SYNTHESIS: 3 LIFE SCIENCE ACADEMICS - 2014
Posted on: Tue, 10 Jun 2014 16:08:46 +0000