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Today we are covering from the specification: Parents A B C Progeny (children) 1 2 3 Parents A B Johnny Ball 1 C Progeny (children) 2 3 Zoe Ball Parents A B C John Lennon Progeny (children) 2 1 Julian Lennon 3 Parents A B C Kirk Douglas Progeny (children) 1 2 Michael Douglas 3 How did you do? • You were able to match the parents to the progeny, not only through similarities but also differences. • These are differences within a species. • This is known as intraspecific variation. Variation within species • This relies upon mutations within a species. • This variation is acted upon by selection pressures. • Only the fittest individuals will survive to breed. • This is the way that evolution via natural selection operates. What is interspecific variation? • These are differences between different species. e.g. the differences between a zebra and a horse. Variation • Variation is the existence of variety and differences within and between species. • On the surface organisms may look identical but on closer inspection show a great deal of variation in their genetics, behaviour and lifestyles. Measuring variation • Measuring variation can be a real problem for biologists. • This is because they are measuring some aspect of a living organism and all living organisms are different. • There are also many individuals of each species – it would be difficult to take measurements from each one. Measuring variation - Sampling • Sampling can help to overcome this problem. Measuring variation - Sampling • Sampling can help to overcome this problem. What do you understand the term “sampling” to mean? Measuring variation - Sampling • Sampling involves taking a selection of individuals from the target population (the population being investigated). • These individuals will represent the population as a whole. • The sample should be unbiased and representative of the whole population. Measuring variation - Sampling • However, sampling is not always reliable. Why not? The problem with sampling • Sampling Bias – The selection process may be biased. The investigators may be making unrepresentative choices, either deliberately or unwittingly. • Chance – Even is sampling bias is avoided, the individuals chosen, by pure chance, may not be representative. Random sampling can help with these problems. But how is this done?! Using a large sample size and appropriate analysis of data collected will also help! Genetic Variation • Every person on Earth has their own unique genetic make-up (unless they are an identical twin). • Most of our 25,000 genes are controlled by more than 1 allele. • A few traits are determined by a single allele e.g. sex, blood group, inherited diseases. • Mutations - caused by miscopying of the DNA of gametes resulting in changes in (or loss of) proteins. Environmental Variation • Most variables are affected by the environment. • Skin colour, weight, height, dialects, accents etc. are all influenced by this. Most phenotypes are influenced by a combination of genes and the environment. Examples List 5 examples each of variation caused by: – Genetics – Environmental causes – Both genetics and the environment Collect data on the shoe size, eye colour, height and handspan of at least 15 students. Find the mean, median and mode where possible for each set of data. Mass Transport Surprise Test Review • Look at the marks you got on each question. • If your total is 14 or higher, you have passed (with no revision!) – well done! • Remember that all work you do from NOW will build on this score. • What do you need to do to improve? HINT 1: Revise. HINT 2: Review/consolidate your work each week. HINT 3: Ask for help. Homework • Find the mark schemes to the questions on the test. • Annotate your test answers. • Ask for help if you don’t understand something. • Have your annotated test ready to show me next Friday (6th Feb). Examples List 5 examples each of variation caused by: – Genetics – Environmental causes – Both genetics and the environment Collect data on the shoe size, eye colour, height and handspan of at least 15 students. Find the mean, median and mode where possible for each set of data. Types of Variation - Continuous • The full range of variables between 2 extreme values. • Examples in nature include : height, weight, length, size. • Data is normally presented as a line graph and forms a normal distribution (a bell-shaped curve). Types of Variation - Discontinuous • Also known as discrete variables. • Variables are assigned to clearly defined categories or distinct groups. • Examples include : sex, blood groups, colour • Data usually presented as a bar graph. Appropriate Analysis – Standard Deviation A measure of spread about the mean. Around 95% of values lie within 2 standard deviations of the mean. Appropriate Analysis – Standard Deviation s = standard deviation (sometimes written as 𝜎) Σ = sum of (sigma) x = measured value (from the sample) 𝑥 = mean value (x bar) n = total number of values in the sample Appropriate Analysis – Standard Deviation • Could be asked to calculate it in the EMPA. • For the exam, never asked to calculate but could be asked to interpret. • Can use pen and paper or a calculator. Example: Calculate the standard deviation of the following numbers: 1, 3, 4, 6, 7, 8, 10, 12, 15, 20 Step 1 – calculate the mean Step 2 – calculate (x - 𝒙) for each number… Mean = 𝑥 = 8.6 x 𝑥 (x - 𝒙) 1 3 4 6 7 8 10 12 15 20 8.6 8.6 8.6 8.6 8.6 8.6 8.6 8.6 8.6 8.6 -7.6 -5.6 -4.6 -2.6 -1.6 -0.6 1.4 3.4 6.4 11.4 x 𝑥 (x - 𝒙) (x - 𝒙)2 1 8.6 3 8.6 4 8.6 6 8.6 7 8.6 8 8.6 10 8.6 12 8.6 15 8.6 20 8.6 -7.6 -5.6 -4.6 -2.6 -1.6 -0.6 1.4 3.4 6.4 11.4 57.76 31.36 21.16 6.76 2.56 0.36 1.96 11.56 40.96 129.96 Σ (x - 𝒙)2 = 304.4 = 33.822 = 5.816