Variation and Inheritance (SQA National 5 Biology): Exam Questions

The ability of a person to roll their tongue is a dominant characteristic represented by the symbol R.

(i) A male with the genotype Rr and a female with genotype rr had a child who was unable to roll their tongue.

State the genotype of their child.

[1]

(ii) Tick (✓) one box to identify whether the child’s genotype is homozygous or heterozygous and give a reason for your choice.

[1]

Homozygous Heterozygous

Reason......................................................................................

(iii) The male and female are having another child.

Predict the percentage chance that this child will be able to roll their tongue.

[1]

............................%

State which type of variation is shown by tongue-rolling ability.

The height of some cattle was measured, and the presence or absence of horns was noted.

Which row in the table is correct?

Progressive retinal atrophy (PRA) is a rare condition in some dogs, such as cockapoos, that can result in blindness.

PRA is caused by the inheritance of the recessive form of a particular gene, which is represented by r.

Depending on their genotype, a dog’s phenotype can be described as affected, unaffected or a carrier.

A cockapoo breeder tested the DNA of a female dog and three male dogs before choosing which pair to breed. The results are shown in the table.

(i) Complete the table by adding the phenotype for male 2 and male 3.

[1]

(ii) State the term used to describe the genotype of a carrier of PRA.

[1]

(iii) The breeder selected a male based on their DNA results for this condition.

The offspring were as follows:

4 unaffected and 4 carriers

Which male was chosen to breed with the female?

[1]

Male.....................................

Another breeder did not carry out DNA tests before breeding a pair of cockapoos. All their offspring were affected by PRA.

Give the genotypes of the parents in this cross.

Male genotype................................ Female genotype ..................................

Give the term used to describe different forms of a gene.

In mice, the dominant form of one gene (B) determines black coat colour and the recessive form (b) determines brown coat colour.

If two heterozygous mice were crossed, the expected phenotypes of the offspring would be

A recessive allele is expressed in an individual’s phenotype when the:

Cholesterol is a fatty substance found in blood. High cholesterol levels can be caused by a condition known as familial hypercholesterolemia (FH).

The following diagram shows part of a family tree showing the inheritance of FH.

‘A’ represents the FH allele.

‘a’ represents the non-FH allele.

Use the information given about the male in the parental generation to explain how it is known that the FH allele is dominant.

The unaffected female in the F₂ generation has a child with a male who is homozygous dominant for FH.

State the percentage chance of their child having FH.

......................%

Identify the type of variation shown by FH.