Scheme of Work Cambridge International as & a level

16: Inheritance

Syllabus ref. and Key Concepts (KC)	Learning outcomes	Suggested teaching activities
16.1 Passage of information from parents to offspring KC1 KC3	16.1.1 Explain the meanings of the terms haploid (n) and diploid (2n). 16.1.2 Explain what is meant by homologous pairs of chromosomes. 16.1.3 Explain the need for a reduction division during meiosis in the production of gametes. 16.1.4 Describe the behaviour of chromosomes in plant and animal cells during meiosis and the associated behaviour of the nuclear envelope, the cell surface membrane and the spindle. 16.1.5 Interpret photomicrographs and diagrams of cells in different stages of meiosis and identify the main stages of meiosis. 16.1.6 Explain that crossing over and random orientation (independent assortment) of pairs of homologous chromosomes and sister chromatids during meiosis produces genetically different gametes. 16.1.7 Explain that the random fusion of gametes at fertilisation produces genetically different individuals.	Introduce the topic of meiosis by reinforcing learners’ knowledge of mitosis from Topic 5. Display a range of multiple-choice questions from Paper 1 as stimuli on the board. Using these, host a class discussion related to the purpose of mitosis, the sub-stages and the importance of its control. Lead a discussion to help learners understand the need for a reduction division during meiosis in the production of gametes. (F) Learners choose two different organisms, e.g. fruit fly (n=4) and humans. Using 2^n, learners work out how many different types of gamete can be formed with two homologous pairs assorting randomly and independently at metaphase I of meiosis. (I) Learners undertake a practical activity to examine the stages of meiosis in the locust testis or prepared slides of an immature anther. Staining cells allows them to see the chromosomes, and observe the stages of meiosis. Learners produce annotated diagrams to outline the formation of pollen grains and embryo sacs. They use a calibrated eyepiece graticule to measure the drawings, and add a scale bar to the drawing. (I) Learners model the process using pipe cleaner or string models of different colours, with sticky labels for alleles. It is useful to have three homologous pairs of chromosomes, of three different sizes or colours. Mobile phones or digital cameras can be used to capture these events. Learners show the behaviour of two homologous pairs of chromosomes in meiosis I and II, including ways to represent random segregation of pairs of alleles and even crossing over (scissors will be required). Animations of meiosis are very useful, as they will show how in meiosis II the spindle forms 90 degrees to the positon of the spindle in meiosis I, and how different-coloured homologous chromosomes are able to swap material during crossing over. Sources include: www.sumanasinc.com/webcontent/animations/content/meiosis.html, www.johnkyrk.com/meiosis.html, www.wiley.com/college/test/0471787159/biology_basics/animations/meiosis.swf vcell.ndsu.edu/animations/meiosis/index.htm and http://highered.mheducation.com/sites/0072495855/student_view0/chapter28/animation__unique_features_of_meiosis.html Animations of crossing over are also useful. Sources include: http://highered.mheducation.com/sites/0072495855/student_view0/chapter28/animation__how_meiosis_works.html www.dnaftb.org/11/animation.html Independent assortment: www.sumanasinc.com/webcontent/animations/content/independentassortment.html