year 9 biology topic inheritance and selection
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KS3 Biology
9A Inheritance and Selection
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9A Inheritance and Selection
Contents
Types of variation
Causes of variation
Summary activities
Variation investigation
Selective breeding
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What characteristics have been passed on in this family?
Family characteristics
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The members of this family tree are related and so they share certain similar characteristics.
Inherited characteristics
Shared family characteristics are inherited from parents.So why don’t all family members look exactly alike?
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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?
Different types of variation
People are similar, but not identical, to their parents or each other. The differences in a species are called variation.
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Variation – environmental or inherited?
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9A Inheritance and Selection
Contents
Types of variation
Causes of variation
Summary activities
Variation investigation
Selective breeding
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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
Inherited characteristics only?
natural hair colour
blood group
some inherited diseases
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From a cell to DNA
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Fertilization and cell division – animation
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Identical twins – animation
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Non-identical twins – animation
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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?
What causes other features?
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.
Is nose shape an inherited or environmental characteristic?
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Variation in humans can be due to inherited factors, environmental factors or a combination of both factors:
Inherited variationWhen 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.
Variation summary
Environmental variationSome 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.
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9A Inheritance and Selection
Contents
Types of variation
Causes of variation
Summary activities
Variation investigation
Selective breeding
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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.
78.5 108.3 111.3 102.1 94.4113.2 100.2 95.7 109.7 113.583.2 106.4 102.1 99.8 102.4118.1 105.6 112.7 103.8 89.2110.8 105.2 112.6 93.8 88.999.6 109.4 99.8 109.4 108.884.8 91.9 97.1 91.7 111.898.4 97.5 109.0 92.1 99.2100.4 98.6 103.7 109.3 104.6102.3 87.4 97.3 119.3 96.1
Variation investigation – beefsteak tomatoes
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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.
Variation investigation – beefsteak tomatoes
What does this graph show?
Distribution of Mass of Beefsteak Tomatoes
mass (g)
fre
qu
enc
y
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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:
40.0 62.2 65.3 58.1 73.074.4 61.3 71.0 48.1 71.659.0 63.9 64.4 44.9 59.860.5 71.1 62.0 64.4 65.756.3 55.7 50.2 55.6 52.359.4 68.3 61.8 54.7 59.449.7 71.9 71.2 46.5 42.058.6 60.6 63.7 64.5 59.643.1 58.2 60.1 68.3 72.557.2 63.1 48.5 64.5 47.7
Variation investigation – plum tomatoes
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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.
Variation investigation – plum tomatoes
Distribution of Mass of Plum Tomatoes
mass (g)
fre
qu
enc
y
What does this graph show?
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Variation investigation – comparing results
Compare the frequency graphs for the masses of the beefsteak and plum tomatoes.
mass (g)
fre
qu
enc
y
Distribution of Mass of Beefsteak Tomatoes
Distribution of Mass of Plum Tomatoes
fre
qu
enc
y
mass (g)
Are there any differences between the two sets of results?
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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?
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?
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9A Inheritance and Selection
Contents
Types of variation
Causes of variation
Summary activities
Variation investigation
Selective breeding
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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.
What is selective breeding?
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Selective breeding – true or false?
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9A Inheritance and Selection
Contents
Types of variation
Causes of variation
Summary activities
Variation investigation
Selective breeding
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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.
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Anagrams
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Multiple-choice quiz