9A Inheritance and Selection KS3 Biology 9A Inheritance and Selection

9A Inheritance and Selection Contents 9A Inheritance and Selection Types of variation Causes of variation Variation investigation Selective breeding Summary activities

Family characteristics What characteristics have been passed on in this family?

Inherited characteristics The members of this family tree are related and so they share certain similar characteristics. Shared family characteristics are inherited from parents. So why don’t all family members look exactly alike?

Different types of variation People are similar, but not identical, to their parents or each other. The differences in a species are called variation. Variation can come about for two reasons. What are they? 1. People inherit characteristics from both of their parents and each person gets a different combination of features. This is called inherited variation. 2. Other characteristics are affected a person’ surroundings. This called environmental variation. Which features are environmental and which are inherited?

Variation – environmental or inherited? Note that this activity may raise some discussion, as some of the features are of course affected by both genetics and environment. The answers for this activity have been worked out on the most simple scenario. See the following two slides for a discussion of the more real but a bit more complicated situation.

9A Inheritance and Selection Contents 9A Inheritance and Selection Types of variation Causes of variation Variation investigation Selective breeding Summary activities

Inherited characteristics only? Deciding whether a characteristic is inherited or environmental can cause a lot of discussion. Scientists have now decided that only four features are truly inherited and not affected by the environment at all. What are the four truly inherited characteristics? natural eye colour natural hair colour blood group some inherited diseases

From a cell to DNA

Fertilization and cell division – animation

Identical twins – animation

Non-identical twins – animation

What causes other features? Is nose shape an inherited or environmental characteristic? The shape of this person’s nose is just like their mum’s nose. However their nose was broken and ended up with a kink in it. So, the initial nose shape was inherited, but over time it has been affected by the environment. Apart from eye colour, natural hair colour, blood group and some inherited diseases, all other features are caused by a mixture of inheritance and environmental factors. What environmental factor might affect skin colour?

Variation summary Inherited variation Environmental variation Variation in humans can be due to inherited factors, environmental factors or a combination of both factors: Inherited variation When humans reproduce via sexual reproduction, the nuclei of the male sex cell and the female sex cell fuse. This cannot happen the same way twice, which makes each individual unique. Environmental variation Some features are due to the conditions in a person’s surroundings. For example, accent is just affected by environment but skin colour is due to both inherited and environmental factors.

9A Inheritance and Selection Contents 9A Inheritance and Selection Types of variation Causes of variation Variation investigation Selective breeding Summary activities

Variation investigation – beefsteak tomatoes Eric bought 50 beefsteak tomatoes for his restaurant. The mass of each tomato was measured (in grams) and the results are given in the following table. If possible get pupils to use a spreadsheet to draw the graph.

Variation investigation – beefsteak tomatoes The masses of the beefsteak tomatoes can be made into a frequency graph by counting how many tomatoes weigh between 78 g and 82 g, 82 g and 96 g and so on. Distribution of Mass of Beefsteak Tomatoes mass (g) frequency What does this graph show?

Variation investigation – plum tomatoes Eric also bought 50 plum tomatoes from the local farm, which were also weighed. The masses (in grams) of this second type of tomatoes are listed in the table below: If possible get pupils to use a spreadsheet to draw the graph.

Variation investigation – plum tomatoes The masses of the plum tomatoes can be displayed in a frequency graph by counting how many tomatoes weigh between 40 g and 44 g, 44 g and 48 g and so on. Distribution of Mass of Plum Tomatoes mass (g) frequency What does this graph show?

Variation investigation – comparing results Compare the frequency graphs for the masses of the beefsteak and plum tomatoes. mass (g) frequency Distribution of Mass of Beefsteak Tomatoes Distribution of Mass of Plum Tomatoes frequency mass (g) Are there any differences between the two sets of results?

Variation investigation – analyzing results Other questions to consider when comparing the frequency graphs for the masses of the beefsteak and plum tomatoes. What can you say about the variation of mass within each species of tomato and the variation between the two sets of results? Are there any other measurements of the tomatoes that can be easily recorded and would show a similar set of results to the measurements of mass? Some quantities cannot be measured immediately but are important to those who grow and those who buy a crop of tomatoes, e.g. disease resistance and time taken to ripen. Can you think of any more quantities like this?

9A Inheritance and Selection Contents 9A Inheritance and Selection Types of variation Causes of variation Variation investigation Selective breeding Summary activities

What is selective breeding? Selective breeding is a process used to produce different breeds of animals or varieties of plants that have useful characteristics. Farmers can choose individual cows to mate in order to produce a generation of cows that will yield more milk. Apple growers want to produce a type of apple that is tasty and resistant to disease. This can be done by crossing a variety of apple known for taste with another variety that shows strong resistance to disease.

Selective breeding – true or false?

9A Inheritance and Selection Contents 9A Inheritance and Selection Types of variation Causes of variation Variation investigation Selective breeding Summary activities

characteristics – The features of a living thing. Glossary characteristics – The features of a living thing. environmental variation – Differences in characteristics caused by surroundings or living conditions. inherited variation – Differences in characteristics that are passed on from parents to offspring. natural selection – Passing on inherited characteristics that make living things best adapted for survival. selective breeding – Producing specific offspring that have useful characteristics of both parents. variation – The differences in characteristics between living things.

Anagrams

Multiple-choice quiz