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KS3 Biology. 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?.

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KS3 Biology

9A Inheritance and Selection


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Contents

9A Inheritance and Selection

Types of variation

Causes of variation

Variation investigation

Selective breeding

Summary activities


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Family characteristics

What characteristics have been passed on in this family?


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Inherited characteristics

The members of this family tree are related and so they share certain similarcharacteristics.

Shared family characteristics are inherited from parents.

So why don’t all family members look exactly alike?


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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. Peopleinherit 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 calledenvironmental variation.

Which features are environmental and which are inherited?



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Contents

9A Inheritance and Selection

Types of variation

Causes of variation

Variation investigation

Selective breeding

Summary activities


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Inherited characteristics only?

natural eye colour

natural hair colour

blood group

some inheriteddiseases

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?






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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?


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Variation summary

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.


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Contents

9A Inheritance and Selection

Types of variation

Causes of variation

Variation investigation

Selective breeding

Summary activities


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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.


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Variation investigation – beefsteak tomatoes

Distribution of Mass of Beefsteak Tomatoes

frequency

mass (g)

The masses of the beefsteak tomatoes can be made into a frequency graph by counting how many tomatoes weigh between 78g and 82g, 82g and 96g and so on.

What does this graph show?


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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:


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Variation investigation – plum tomatoes

Distribution of Mass of Plum Tomatoes

frequency

mass (g)

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.

What does this graph show?


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Variation investigation – comparing results

Distribution of Mass

of Beefsteak Tomatoes

Distribution of Mass

of Plum Tomatoes

frequency

frequency

mass (g)

mass (g)

Compare the frequency graphs for the masses of the beefsteak and plum tomatoes.

  • Are there any differences between the two sets of results?


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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?


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Contents

9A Inheritance and Selection

Types of variation

Causes of variation

Variation investigation

Selective breeding

Summary activities


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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.



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Contents

9A Inheritance and Selection

Types of variation

Causes of variation

Variation investigation

Selective breeding

Summary activities


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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.