9A Inheritance and Selection

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Variation

Look closely at the picture below. Do the children shareany features or characteristics with their parents?


Variation

In general we can see that children are similar, but not identical, to their parents. Differences occur because children inheritinherit characteristics from both their parents and they can be affected by their environment. This is true for both animals and plants.

Variation can come about for two reasons:

1. Some features can be inherited. That means that you get them from your parents.

2. Other characteristics are affected by the environment.


So what causes variation?

Remember back to the photo of the group of people. They are in fact all RELATED. So you might notice things about them that are quite similar. That is because some of their features were inherited from their parents.

But do they look exactly alike?


Animals and plants which reproduce sexually therefore transfer characteristics to their offspring through the nuclei of the sex cells in the same way. This means that these offspring are also unique.


No, of course they don’t! There are two reasons for this:

Firstly humans reproduce via sexual reproduction. This involves the fusion of the male sex cell and the female sex cell. The nucleus in these sex cells contains information about the parents. This cannot happen the same way twice. This makes each individual unique.


Genes








Secondly some features are caused by conditions in your surroundings. For example your parents might be tall, but, if you don’t get all the food you need you might not be tall at all!

Additionally think of a runner. They need speed and stamina. These things are not inherited – they are improved by training and diet.

These features are called environmental.



Environmental or Inherited?


The activity on the previous page might have brought up a bit of discussion. The truth is that it made it all seem very simple.

It is in fact really a lot more complicated. Scientists have now decided that only 4 features are truly inherited and not affected by environment at all.

Can you guess what they are?

1. Eye colour2. Natural hair colour3. Blood group4. Some inherited diseases


So what about the other features?

The other features are caused by a mixture of inheritance and environment.

For example the shape of your nose. You may have a nose that looks just like your Mum’s. But if you were in an accident you might break your nose and put a bit of a kink in it. So your initial nose shape was probably inherited but over time it has been effected by environment.

What part of the environment might effect the skin colour that you were born with?


Variation Investigation

Eric bought a particular variety, called beefsteak, of tomatoes for his restaurant. All the tomatoes were weighed and the results (measured in grams) are given in the following table:

Investigation

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


If the weight of the tomatoes is made into a frequency histogram by counting how many tomatoes weigh between 78 and 82, 82 and 96, etc. What does this type of graph show?

Results

Distribution of Beefsteak Tomato Mass

0

2

4

6

8

10

78 82 86 90 94 98 102 106 110 114 118 122

Mass (g)

Fre

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cy


Variation Investigation

Eric also bought a ray of plum tomatoes from the local farm, these were also weighed. Their masses (in grams) are listed in the table below:

Investigation

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


If the weight of the plum tomatoes is made into a frequency histogram as in the previous example, etc. What does this type of graph show?

Results

Distribution of Plum Tomato Mass

0

2

4

6

8

10

12

40.0 44.0 48.0 52.0 56.0 60.0 64.0 68.0 72.0 76.0

Mass (g)

Fre

qu

en

cy


Discussion

The previous slides showed the results of a simple experiment.• Are there any differences between the two sets of results?

• 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 quantities which can be measured immediately and which would show a similar set of results. Some quantities cannot be immediately measured but are important to the people who grow and buy the crop of, in this case, tomatoes. These are:

• Resistance to disease.

• Time taken to ripen.

Can you think of any more?


Selective breeding

This is a process used by humans to produce different breeds of animals or varieties of plants.

Farmers may choose individual cows to mate which will produce a newer generation of cows that are better at producing milk.

Apple growers would like to produce a type of apple which is tasty but also resistant to disease. They could do this by crossing a variety of apple known for taste with another type which shows strong resistance to disease.

wheat


Selective breeding

Documents

9A Inheritance and Selection