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IB Biology SLD3.2 InheritanceQuestion Bank

D3.2 Inheritance

Question 1

[Maximum number: 5]

Dementia is a term used to describe a group of symptoms that are caused by a decline in brain function. People with dementia have problems with memory, language and behaviour.

Alzheimer's disease is the most common cause of dementia. Scientists investigated the effect of a drug called donanemab on people with Alzheimer's disease. They divided them into two groups:
- The treatment group received regular injections of a solution containing donanemab.
- The control group received regular injections of a solution without donanemab.

The scientists used the Alzheimer's Disease Rating Scale (ADRS) to measure brain function. The lower the score on this scale, the worse the brain function. The scientists calculated the mean ADRS score for each group at intervals over 76 weeks. They then calculated the mean change from their initial score at the start of the investigation (baseline).

Their results are shown in the graph.

Question image

Question 1(d)

(a)

SNAP-25 (Synaptosomal-Associated Protein) is a protein found in the brain.
In a different investigation, scientists measured the concentration of SNAP-25 in the cerebrospinal fluid (CSF) of three groups of people:
- 36 people without Alzheimer's disease (No AD)
- 18 people with Alzheimer's disease who had mild dementia (AD mild)
- 24 people with Alzheimer's disease who had severe dementia (AD severe)

Their results are shown in the box-and-whisker plot.

Question image

Estimate the median concentration of SNAP-25 in CSF for the AD mild group.
ngL−1\mathrm{ng} \mathrm{L}^{-1}

[ 1 ]

Question 1(e)

(b)

Using your knowledge of box-and-whisker plots, state what the data point shown as a triangle represents.

[ 1 ]

Question 1(f)

(c)

Using all the information provided, evaluate the use of SNAP-25 concentration as a potential marker to help confirm a diagnosis of Alzheimer's disease.

[ 3 ]

Question A2

Question A2(c)

(a)

Explain how diet can reduce the consequences of phenylketonuria (PKU).

[ 3 ]

Question 2

Question 2(b)

(a)

Explain the causes, consequences and treatment of phenylketonuria (PKU).

[ 3 ]

Question 2

Question 2(a)

Question 2(a)(i)

(a)
(i)

Using the table, state whether recessive, dominant and codominant alleles are expressed in heterozygous and homozygous genotypes by writing yes, no or both.

Table
[ 2 ]

Question 2(a)(ii)

(ii)

State two alleles in blood groups that are codominant.

[ 1 ]

Question 2

[Maximum number: 3]

The dolichos bean (Lablab purpureus) is cultivated as a food crop in tropical countries. Leaf cells in L. purpureus have 24 chromosomes.

Question 2(b)

(a)

L. purpureus can have purple or white flowers. Two pure-breeding varieties were crossed: HA 4 with white flowers and GL 424 with purple flowers. All of the F1F_{1} plants had purple flowers. The F1F_{1} plants were self-pollinated to produce an F2F_{2} generation. There were 97 plants with purple flowers and 38 plants with white flowers in the F2F_{2} generation.

Using a Punnett grid, explain the results of this cross.

[ 3 ]

Question 12

[Maximum number: 1]

If a man with blood group O and a woman with blood group AB have children, which blood group(s) could the children have?

A

Group O only

B

Groups A and B only

C

Group AB only

D

Groups O, A, B and AB

Question 12

[Maximum number: 1]

What is the difference between dominant, recessive and codominant alleles?

Dominant allele

Recessive allele

Codominant allele

only affecting the phenotype when in a homozygous state

always affecting the phenotype

both alleles affect the phenotype

always affecting the phenotype

both alleles affect the phenotype

only affecting the phenotype when in a homozygous state

always affecting the phenotype

only affecting the phenotype when in a homozygous state

both alleles affect the phenotype

both alleles affect the phenotype

only affecting the phenotype when in a heterozygous state

always affecting the phenotype when in a heterozygous state

Question 3

Question 3(b)

(a)

Explain the causes and consequences of phenylketonuria (PKU).

[ 4 ]

Question A3

[Maximum number: 3]

A3. Describe the causes, consequences and diagnosis of phenylketonuria (PKU).

Question 13

[Maximum number: 1]

Which statement defines alleles?

A

They are the different forms of a gene that have the same effect on the phenotype.

B

They are the similar forms of a gene in different positions of a chromosome.

C

They are the various forms of a gene with slight differences in their base sequences.

D

They are the different forms of a gene coding for identical polypeptide chains.

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