A Level Biology 6.1.2 L3 Workbook

L3 Genetic diagrams – monogenetic crosses
Starter
1. The apple tree, Malus domestica, is a species that humans have selectively bred.
Circumference and seed production, listed in Table 1.1, are two features of apple tree fruit that vary between individuals.
Complete Table 1.1 by writing the correct word or phrase in each box to describe the type of variation shown by each feature.
Type of graph used to

Feature Cause of feature Number of genes involved
present data
Circumference (mm)
Seed-containing / seedless
Table 1.1
[3]
2. A gene codes for the production of lactase. This gene is normally switched off after an infant moves to adult food. Almost all adult
mammals are unable to digest lactose. They are said to be lactose intolerant. Humans are an exception.
Most humans have a genetic mutation that prevents the shutdown of lactase production.
State what structural detail of a polypeptide is altered by gene mutations.
[1]
3. Which of the following processes is important in determining the overall body plan of an organism?
A endocytosis
B exocytosis
C meiosis
D mitosis
Your answer [1]
4. Genes are not expressed during cell division because chromosomes are more tightly wound around histone proteins than during
interphase.
Which of the following shows the level at which gene expression is being controlled when DNA is more tightly wound during cell
division?
A post-transcriptional
B post-translational
C transcriptional
D translational
Your answer [1]

Monogenetic inheritance
Incomplete dominance
Codominance
a) Draw a genetic cross diagram for crossing a red snap dragon (CR CR )with a
white snap dragon (CWCW) what colour are the offspring? ( this is called the F1
generation)
b) Draw a genetic cross diagram when two of the offspring are crossed, what
colour are the offspring? (F2 generation)
Exam questions
1. The inheritance of some alleles depends on the sex of the individual.
In birds, sex is determined by a combination of Z and W chromosomes.
Male birds have two Z chromosomes and female birds have one Z chromosome and one W chromosome.
i. The chromosomes used to determine sex inheritance are given different letters in birds and mammals.
Identify one other way in which the sex determination in birds is different from sex determination in mammals.
[1]
ii. A pigeon is a bird. The colour of pigeon feathers is determined by a single gene on the Z chromosome.
The feather colour gene has three alleles.

ZA = red
ZB = blue
Zb = brown
ZA is dominant to ZB and Zb
ZB is dominant to Zb
The W chromosome contains no gene for feather colour.
A pigeon with the genotype ZA Zb was crossed with a pigeon with genotype ZBW.
Complete the answer lines below to show this genetic cross.
Parent genotypes: ZA Zb × ZBW
Parent phenotypes:
Gametes:
Offspring genotypes:
Offspring phenotypes:
[4]
2. The inheritance of some alleles depends on the sex of the individual.
In birds, sex is determined by a combination of Z and W chromosomes.
Male birds have two Z chromosomes and female birds have one Z chromosome and one W chromosome.
i. The chromosomes used to determine sex inheritance are given different letters in birds and mammals.
Identify one other way in which the sex determination in birds is different from sex determination in mammals.
_________________________________________________________________________________________________ [1]
ii. A pigeon is a bird. The colour of pigeon feathers is determined by a single gene on the Z chromosome.
The feather colour gene has three alleles.

ZA = red
ZB = blue
Zb = brown
ZA is dominant to ZB and Zb
ZB is dominant to Zb
The W chromosome contains no gene for feather colour.
A pigeon with the genotype ZA Zb was crossed with a pigeon with genotype ZBW.
Complete the answer lines below to show this genetic cross.
Parent genotypes: ZA Zb × ZBW
Parent phenotypes:
Gametes:
Offspring genotypes:
Offspring phenotypes:
[4]
3(a). In domesticated, farmed pigs, the following two traits have been studied:
The allele for curly tail, T, is dominant to the allele for straight tail, t.
The allele for pink skin (dermis), D, is dominant to the allele for black skin, d.
i. Draw a genetic diagram to show the results of crossing pigs that are heterozygous for both traits, tail and skin. Use the letters
given above.
parental genotypes .......................................... ..........................................

gametes .......................................... ..........................................
F1 offspring genotypes
offspring phenotypes
phenotype ratio
[5]
ii. Describe in words how this phenotypic ratio might be different if the two genes were autosomally linked.
[1]
END OF QUESTION PAPER

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L3 Genetic diagrams – monogenetic crosses

Type of graph used to

State what structural detail of a polypeptide is altered by gene mutations.

Your answer [1]

Your answer [1]

In birds, sex is determined by a combination of Z and W chromosomes.

The feather colour gene has three alleles.

The W chromosome contains no gene for feather colour.

Complete the answer lines below to show this genetic cross.

Parent genotypes: ZA Zb × ZBW

2. The inheritance of some alleles depends on the sex of the individual.

In birds, sex is determined by a combination of Z and W chromosomes.

The feather colour gene has three alleles.

The W chromosome contains no gene for feather colour.

Complete the answer lines below to show this genetic cross.

Parent genotypes: ZA Zb × ZBW

parental genotypes .......................................... ..........................................

END OF QUESTION PAPER

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