© KCL. WCED. PENTECH Variation LOOK around the learners in your class. They all have a lot of characteristics in common because they are human. But they also have features that are different and a few which are unique. Some of these features are inherited from our parents such as the type of ear lobe or ability to roll our tongue. Others are caused by the environment and way we live, such as having scars on our skin or an accent. Some of our characteristics can differ only a little bit from other people. They vary gradually and show a wide range. Examples of this, such as height and hand span, are known as continuous variation. Other features such, right or left handedness and finger prints are more clear -cut. They fall into distinct groups. These differences are termed discontinuous variation. STUDY the characteristics of people in your group carefully and COMPLETE the table Visible characteristic Caused by the environment Continuous or discontinuous Of the features you think have been inherited, DISCUSS which have come from your mother or father. Inherited from parents 1.

© KCL. WCED. PENTECH Variation 2. Twins have often been studied to understand which characteristics are inherited and which determined by the environment. Identical twins have exactly the same genetic instructions for building their body. If they are brought up together in the same family they also experience a similar environment. If they are separated and brought up by different families the environmental conditions effecting them could be very different. Non-identical (fraternal) twins develop at the same time but will not necessarily be any more alike genetically than brothers and sisters born at different times. STUDY this table giving information about the average differences in certain physical characteristics between pairs of twins. Difference in 50 pairs of identical twins reared together 50 pairs of non-identical twins reared together 19 pairs of identical twins reared apart Height (cm) Weight (kg) Head length (mm) Head width (mm) DISCUSS and write about the evidence supporting which of these characteristics are inherited and which are also effected by the environment the twins lived in. DECIDE what other information you would now like to have?

© KCL. WCED. PENTECH Variation At a fish farm, all the fertilised eggs are allowed to develop in the same controlled environment. Any variation between individuals will be mainly due to genetic differences. Graph showing the variation in length of a sample of 250 fish in Number of fish Length in cm DESCRIBE what the graph shows and which factors should be kept constant in the environment. DISCUSS in which ways you think the pattern would be different if the fish had been fed more food?

© KCL. WCED. PENTECH Variation Ranu and Chris are studying plant growth on their agriculture course. They decided to investigate the variation in height of Sorghum plants. This is important information if the grain is to be harvested by machine. They soon realised that they could not measure every plant in the field but were not sure which plants to choose. Please try to help them. DESIGN your own investigation to measure the variation in height of Sorghum plants. DECIDE - on the equipment you will need and how you will use it - how many plants you would need to measure and at what time of year - how you would choose which plants to measure in the field 4. Ranu’s procedure on 30th January 1) Plants taken from 20 randomly selected areas. 2) Plants to be measured selected at random. 3) Height of 15 plants measured in each area. Chris’s procedure on 6th February 1) Plants taken from 4 corner areas of the field. 2) Plants measured from the middle of each area. 3) Height of 25 plants measured in each area. READ and DISCUSS the investigation plans of each student

© KCL. WCED. PENTECH Variation Height interval (cm) Number of plants Ranu Chris Number of plants Height interval of plants PLOT line graphs of both students results. 5. DISCUSS the different results for Sorghum plants

© KCL. WCED. PENTECH Variation The students then discuss their investigations, compare results and try to draw conclusions. STUDY each of their statements. DISCUSS whether you agree or disagree. WRITE down evidence to support what you think. Ranu thinks that her procedure is better and her results more reliable in showing variation in the height of plants. Chris thinks his results can be compared to Ranu’s even though he was a week late in carrying out his investigation. Ranu and Chris think that the height in Sorghum shows continuous variation. Ranu concludes that height of Sorghum plants is entirely genetically controlled. 6.

© KCL. WCED. PENTECH Variation It is said that no two people have the identical fingerprints. The patterns of fingerprints can however be classified into four main types. The bar graph shows an analysis of 100 forefinger prints Number of fingerprints LoopWhorlArchCompound DISCUSS and WRITE about the type of variation shown by fingerprints and how they are acquired. Do you have the same pattern of distribution in your class? LoopWhorlCompoundArch 7.