Variation L O Understand different types of variation

Variation L. O: Understand different types of variation Grade 4: List some examples of human variation and categorise into genetic causes, environmental causes, or both. Grade 6: List some examples of variation in plants and categorise these as being due to genetic causes, environmental causes, or both. Grade 8: Explain why some traits are only due to genetic causes. Explain why it is so hard to get valid results from identical-twin studies and discuss some of the issues scientists face when conducting these.

Who? What? Why? When? Where? Ho. W?

Genetic causes of variation Many characteristics are caused by the genes that we inherit from our parents. These are never exactly the same as either parent’s genes, but a new combination. When sex cells (gametes) are produced in the parents, genes are swapped between the chromosomes so that they are not exactly the same as the parents’. At fertilisation, any sperm could fuse with the egg, mixing the genes from both parents to form a very different combination. This means that offspring are always different to their parents, creating genetic variation.

Environmental causes of variation It is not just genes that determine a person’s characteristics. What else has an effect on what you are like? what you eat where you live how much exercise you do your education illness and injury

Environmental causes of variation The same goes for plants!! Availability of water Access to nutrients in the soil Availability of sunlight Soil p. H Disease

Inherited and acquired characteristics Some characteristics, such as eye colour and earlobe shape, are only determined by genes. These are called inherited characteristics. Other types of characteristics, such as scars and language, are not inherited but depend on environmental factors. These are called acquired characteristics. Differences in some characteristics, like body mass, are due to a combination of inherited and environmental factors. It can be difficult to say how much influence each factor has.

HIGHER LEVEL Mutation and genetic variation Mutation is a change in the type or amount of DNA and is therefore another cause of genetic variation. Mutations can occur spontaneously – for example, through the incorrect copying of DNA when it replicates, or through the unequal distribution of chromosomes during cell division. Mutations can also be caused by environmental factors, such as radiation (for example, UV radiation from the sun) and certain chemicals. These factors are called mutagens. Some mutations may be beneficial, but many are harmful and increase the risk of developing diseases such as cancer.

TASK • Grade 4: Complete the Inherited vs Environmental Venn diagram and extension question • Grade 6: Complete ‘Twin Studies’ sheet • Grade 8: Complete ‘Twin studies’ sheet including the ‘Student follow-up’ question

Inherited v environment

Blood group Accent Eye colour Speaking French Natural hair colour Skin colour Freckles Weight Scars Height Tooth fillings Ear piercing Tattoos Sporting ability Hair style Intelligence INHERITED Versus ENVIRONMENT

Plenary Review Grade 4 Grade 6 Grade 8

Answers

Variation L. O: Understand different types of variation Grade 4: List some examples of human variation and categorise into genetic causes, environmental causes, or both. Grade 6: List some examples of variation in plants and categorise these as being due to genetic causes, environmental causes, or both. Grade 8: Explain why some traits are only due to genetic causes. Explain why it is so hard to get valid results from identical-twin studies and discuss some of the issues scientists face when conducting these.