Variation and Inheritance

LO: To learn how characteristics can vary.

with…

The Mr Men Match.

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Variation“Variation” is the name given to differences between individuals of the SAME species.

Variation is due to GENETIC or ENVIRONMENTAL causes. For example, consider identical twins:

1) Ways in which Tom and James are the same (caused by genes):

2) Ways in which Tom and James are different (caused by environment):

What’s that then?

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Genes, Chromosomes and DNA

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Where is this information stored?Section of a chromosome:

Genes for eye colour

Genes for hair colour

Genes for blood group:

Different species have different numbers of chromosomes. Humans have 46 (23 pairs) in every cell.

Genes

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Sexual ReproductionThe human egg and sperm cell (“GAMETES”) contain 23 chromosomes each.

When fertilisation happens the gametes fuse together to make a single cell called a ZYGOTE. The zygote has 46 chromosomes (23 pairs).

So what causes variation?

Meet our Mr Men And our Little Misses

Now lets meet their children!

What did we learn from this?

• Children inherit features from their parents

• If two parents have a certain characteristic then their child may show it even more (e.g. Mr Small + Little Miss Tiny = Mr Very Small!)

• Some things such as glasses, scars and muscles we get from our environment, they are not inherited.

Genetic information

• The instructions that make up a plant or animal comes from their parents.

• ½ comes from the sperm and ½ from the egg

• These instructions are found in the nucleus of the cells.

• The instructions for each characteristic are called GENES.

We saw that when Mr Small and Little Miss Tiny produced a child it was even smaller.

What would happen if Mr Very Small had a child with Little Miss Miniscule??

This is called selective breeding and can be used to make larger animals and crops that produce

more fruit

Large fruited Dad Large fruited Mum

Very large fruited child!

This is depending on the strength of the genes...

• Some genes have more clout when it comes to deciding a feature than others.

• “Stronger” genes are known as dominant• “Weaker” genes are known as recessive.

• The gene for brown eye colour is dominant. If one of your parents have brown eyes it is very likely you will too!

• There’s still a small chance of blue eyes but the probability is decreased.

Variation

• Level 4 – Recognise difference between organisms of the same species

• Level 5 – Explain what may have caused some examples of variation within a species

• Level 6 – Suggest why variation might increase an organisms chances of survival

• Level 7 – Explain, using variation, why certain species have become extinct

Variation…your task• You have been asked to produce a poster for Year 8 students to

teach them about ‘variation’.• Use you LOs as your level ladder for this task and tick them off as

you go

• Key words; • Variation• Gene• Inherit• Environmental• Survival• Extinction• Organism

Don’t forget to include the two types of variation and examples of each!

Lets see what you’ve learned:

Farmer Hemming wants to breed cows that are large and meaty so that he can sell them for

more.

1.What advice would you give him in order to produce larger cows?

2. He can’t seem to breed cows with nose rings! Why not?

3. How many chromosomes are in your cells?