Download B3a Worksheet 3: DNA

Worksheet B1h 16
Inherited disorders
1. Scientists have found a rare genetic disorder that can cause short sight.
It is called nanopthalmos.
This is caused by a recessive copy of a gene.
(i)
Write about where in a cell genes are found.
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(ii)
Look at this part of a family tree showing some people with
nanopthalmos.
Nanopthalmos is caused by a recessive allele.
How can you tell this from this family tree?
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[Total: 4]
Worksheet B1h 16 continued
2. Sam has red-green colour blindness.
This means that he cannot tell the difference between red and green colours.
(i)
Red-green colour blindness is an inherited disorder.
Look at the list.
Put a tick () in the box next to another inherited disorder.
[1]
(ii)
In which part of a cell would you find the gene for red-green colour
blindness?
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(iii)
Red-green colour blindness is a result of changes to genes.
Write down the scientific name for the change to a gene.
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(iv)
Sam has an identical twin called Todd.
Todd has the same genes as Sam.
What is the probability that Todd also has red-green colour blindness?
Put a ring around the correct answer.
0%
25%
50%
100%
[1]
[Total: 4]
Worksheet B1h 16 continued
[Higher Tier]
3. Cystic fibrosis is a genetic disorder.
Akinyi is a child that has cystic fibrosis.
It is caused by a recessive allele.
Neither of Akinyi’s parents have cystic fibrosis.
They want to have another child.
(a) What is the probability of their next child having cystic fibrosis?
Draw a genetic diagram to explain your answer.
(Use F for the dominant allele and f for the recessive allele).
probability _____________________________
[2]
(b) Akinyi’s parents are expecting another child.
They are trying to decide whether to have the foetus tested for cystic
fibrosis.
Suggest what they need to consider and why it might be difficult for them to
make such a decision.
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_______________________________________________________________________ [2]
[Total: 4]
Worksheet B1h 16 continued
[Higher Tier]
4. Fred has cystic fibrosis.
He finds it difficult to breathe because there is too much mucus in his lungs.
Cystic fibrosis is an inherited condition.
It is caused by a recessive allele.
(a) Neither of Fred’s parents has cystic fibrosis.
They want to have another child. What is the probability of their next child
having cystic fibrosis?
Draw a genetic diagram to explain your answer.
probability of next child having cystic fibrosis _____________
[2]
(b) Fred gets a lot of chest infections.
When he gets a bacterial infection, his doctor gives him antibiotics.
Fred’s doctor could just give him antibiotics all the time as a precaution.
However, doctors are careful not to use antibiotics more than necessary.
One reason for this is not to waste money.
Write down one other reason.
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_______________________________________________________________________ [1]
(c) Chest infections can be caused by different types of bacteria.
Tests were done on 100 patients with cystic fibrosis.
The tests involved taking a sample from each patient and finding which of
three types of bacteria were present in their system.
The bar chart on the next page shows the results of the tests.
Worksheet B1h 16 continued
Percentage of patients with the bacteria in their system: Staphylococcus aureus,
Pseudomonas aeruginosa, Haemophilus influenzae bacteria
Can you tell from these data how many patients have more than one of these
types of bacteria in their system?
Explain your answer.
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__________________________________________________________________________ [2]
[Total: 5]