Inheritance

Know about some inherited conditions.

Use some rules of inheritance.

Define dominant and recessive.

Starter: Finish this sentence with at least two of your own ideas

If I did not have colour vision I would find it hard to…

Inherited disorders

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Colour blindness can be inherited, along with cystic fibrosis and haemophilia. This is what one type of colour

blindness looks like to the sufferer.

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Colour blindness

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Which one is dominant?

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Dominance can be thought of in terms of which gene will “win”.

For example brown eyes are dominant over blue.

If you inherited a brown eye gene from your dad and a blue eye gene from your mum what colour would your eyes be?

Would this change if you got the brown gene from your mum and blue from your dad?

Dominant and recessive

• Dominant characteristics will always be expressed over recessive.

• If ‘B’ stands for brown and ‘g’ stands for green then what colour eyes will these people have?

• A boy who is ‘BB’ for eye colour.• A girl who is ‘gg’ for eye colour.

• A girl who is ‘Bg’ for eye colour.

Monohybrid crosses

Egg from motherSperm

from

father

Heterozygous - Bg = brown hair

Homozygous - gg = ginger hair

B

g

B

g

BB Bg

Bg ggSo to have a baby with ginger hair you need to inherit

a recessive ginger hair gene from your father and your mother.

Boys and girls

Egg from motherSperm

from

father

Heterozygous - XY = Boy

Homozygous - XX = Girl

X

Y

X

X

XX XX

XY XYSo each time a woman conceives there is a perfect 50/50 chance that the zygote will develop into a boy

or into a girl.

Work to do

• Answer question 1 on page 39.

Inheritance

Know about some inherited conditions.

Use some rules of inheritance.

Define dominant and recessive.

Plenary: Can you roll your tongue? Draw a monohybrid cross to work out how many children out of 4 could not roll their tongue:

R = can roll, r = cannot roll Dad: Rr Mum: rr