Practise Inherited disorders. 14 exam-style questions plus unlimited generated ones on this subtopic, at up to four difficulty levels, with full mark schemes and a progress tracker. Free, no account needed.
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Some disorders are inherited. They are caused by the inheritance of certain alleles. Describe what polydactyly is.
Having extra fingers or toes
Cystic fibrosis (CF) is caused by a recessive allele, f. The dominant allele, F, results in normal cell membranes. Two parents are both carriers of CF. Give the genotype of a carrier of CF.
Ff
Polydactyly is caused by a dominant allele, D. A man who is heterozygous for polydactyly has children with a woman who does not have polydactyly. Give the genotype of the man and the genotype of the woman.
Man Dd; woman dd
A couple are both carriers of cystic fibrosis. They are thinking about using IVF with embryo screening. Give one argument for embryo screening.
It prevents a child being born with a serious disorder, avoiding suffering
Cystic fibrosis is caused by a recessive allele. Give the genotype of a person who has cystic fibrosis. Use F for the dominant allele and f for the recessive allele.
ff
Sample questions
Written for this site in the style of AQA exam questions. They are not taken from real past papers.
Question 1Easy5 marks
Some disorders are inherited. They are caused by the inheritance of certain alleles.
(a) What causes polydactyly? Tick (✓) one box.[1]
A bacterial infection
A dominant allele
A poor diet
A recessive allele
(b) Describe what polydactyly is.[1]
(c) Cystic fibrosis is a disorder of which part of the cell? Tick (✓) one box.[1]
Cell membrane
Cell wall
Mitochondria
Ribosomes
(d) Cystic fibrosis is caused by a recessive allele. What word describes a person who has one copy of this allele but does not have the disorder?[1]
(e) Human embryos can be tested for the alleles that cause genetic disorders. What is this process called?[1]
Show the answer and mark scheme
(a)Answer: A dominant allele
(b)Answer: Having extra fingers or toes
having extra fingers or toes
(c)Answer: Cell membrane
(d)Answer: Carrier
carrier
(e)Answer: Embryo screening
embryo screening
Question 2Medium6 marks
Polydactyly is caused by a dominant allele, D. A man who is heterozygous for polydactyly has children with a woman who does not have polydactyly.
(a) Give the genotype of the man and the genotype of the woman.[2]
(b) Draw a Punnett square to show the possible genotypes of their children. Give the probability that a child will have polydactyly.[3]
(c) Explain why a person cannot be a carrier of polydactyly without having the condition.[1]
Show the answer and mark scheme
(a)Answer: Man Dd; woman dd
man: Dd
woman: dd
(b)Answer: Gametes D and d from the man, d and d from the woman; offspring Dd, Dd, dd, dd; probability 0.5
gametes: D and d (man), d and d (woman)
offspring: Dd, Dd, dd, dd
probability = 0.5 / 50% / ½
(c)Answer: The allele is dominant, so anyone with one copy has polydactyly
the allele is dominant so it is always expressed / one copy causes the condition
Question 3Hard6 marks
Huntington's disease is an inherited disorder of the nervous system. It is caused by a dominant allele, H. Symptoms usually start when a person is between 30 and 50 years old. Jo is 20 years old. Jo's father has Huntington's disease and is heterozygous (Hh). Jo's mother does not have the allele (hh).
(a) Give the probability that Jo has inherited the allele for Huntington's disease. Explain your answer.[2]
(b) Explain why Jo cannot tell from Jo's own health whether Jo has inherited the allele.[1]
(c) Jo has not been tested. Jo's partner does not have the allele. Calculate the probability that their first child will inherit the allele for Huntington's disease. Give your answer as a fraction or a decimal.[2]
(d) Suggest one reason why some people in Jo's position decide not to have a test for the allele.[1]
Show the answer and mark scheme
(a)Answer: ½: Jo's father (Hh) passes on H or h with equal chance, and Jo's mother (hh) can only pass on h
½ / 0.5 / 50%
the father (Hh) passes on H or h with equal chance, and the mother (hh) can only pass on h (so Hh : hh = 1 : 1)
(b)Answer: Symptoms do not usually start until the age of 30 to 50, and Jo is only 20
symptoms do not usually appear until 30 to 50 years old, and Jo is only 20
(c)Answer: ¼ (0.25)
probability that Jo has the allele (½) × probability that Jo passes it on if Jo has it (½)
= ¼ (0.25)
(d)Answer: There is no cure, so knowing could cause great worry
there is no cure, so knowing could cause worry / anxiety / some prefer not to know / concerns about insurance or employment