Practise monohybrid inheritance questions by defining genetic terms, interpreting pedigrees and Punnett squares, and tackling test crosses, ABO and sex-linked traits.
Colour blindness is a characteristic that is inherited. Colour blindness is more common in males than in females.
Fig. 6.1 is a pedigree diagram showing the inheritance of colour blindness in a family.
Fig. 6.1
Define the term inheritance.
Using the symbols B and b, state the genotypes of individual 5 and individual 8 in the pedigree diagram.
5
8
Individual 3 is a carrier of colour blindness because she has one copy of the allele for colour blindness but has normal colour vision.
Describe the evidence from Fig. 6.1 that shows that individual 3 is a carrier.
The garden pea, Pisum sativum, is a plant which has flowers that have both male and female parts. P. sativum is naturally self-pollinating.
Gregor Mendel studied inheritance in the garden pea, P. sativum.
The flowers of P. sativum that he studied were either purple or white. The gene that controls flower colour has two alleles, B and b.
When Mendel crossed purple-flowered plants with white-flowered plants all the plants in the next generation had purple flowers.
Table 4.1 shows five genetic terms that can be applied to Mendel's study of the inheritance of flower colour.
Complete Table 4.1 by stating an example of each genetic term. The first one has been completed for you.
Table 4.1
Test crosses can be used to determine the genotype of a plant with purple flowers.
The genetic diagrams show test crosses for purple-flowered plants with two different genotypes.
Complete the genetic diagrams for test cross 1 and test cross 2.
offspring
genotypes
offspring
phenotypes
test cross 2
purple flowers × white flowers
BB ×
Pickerel weed, Pontederia cordata, is a plant that grows in shallow water on the edges of ponds and lakes in North America.
A few seedlings of these plants are white. The white seedlings cannot make chlorophyll.
Researchers carried out several crosses using pickerel weed plants.
Their results are shown in Table 4.2.
Table 4.2
Select suitable symbols for the alleles and state the possible genotypes of the parents for each cross.
cross 1
cross 2
It is not possible to carry out a test cross with pickerel weed plants.
Suggest why.
Fig. 6.1 is a photomicrograph of a blood clot.
Fig. 6.1
There are four blood group phenotypes A, B, AB and O in humans.
Define the term phenotype.
State the name of the type of inheritance that is shown by blood groups.
State the two possible genotypes for a person who has the phenotype blood group A .
1
2
Colour blindness is a characteristic that is inherited. Colour blindness is more common in males than in females.
Fig. 6.1 is a pedigree diagram showing the inheritance of colour blindness in a family.
Fig. 6.1
Define the term inheritance.
Fig. 6.1 is a photomicrograph of a blood clot.
Fig. 6.1
There are four blood group phenotypes A, B, AB and O in humans.
Define the term phenotype.
Researchers carried out some experiments on tomato plants that were homozygous for fruit colour.
State how the researchers could be sure that the fruit came from homozygous plants.
The diagram shows the inheritance of height in pea plants.
Which plants have a heterozygous genotype?
both parent plants
dwarf parent plant only
both offspring plants
tall parent plant only
Some fruit flies have orange eyes and others have red eyes.
If two orange-eyed fruit flies are crossed, their offspring always have orange eyes.
If two red-eyed fruit flies are crossed, their offspring can have orange eyes or red eyes.
What can be concluded from these observations?
The allele for orange eyes is dominant.
The allele for orange eyes is recessive.
The alleles for orange and red eyes are codominant.
This is an example of sex linkage.
Polydactyly is a condition that can occur in cats and results in affected individuals having extra toes.
The diagram shows the inheritance of the condition in a family of cats.
What does the family tree show about the allele for polydactyly?
It is codominant.
It could be dominant or recessive.
It is dominant.
It is recessive.
Fig. 2.1 shows a dwarf sunflower and a tall sunflower, Helianthus annuus. The height of the dwarf sunflower is 0.45 m and the height of the tall sunflower is 4.5 m .
not to scale
Dwarf plants like the one in Fig. 2.1 have mutant alleles.
Two tall sunflower plants were crossed. 25\% of the offspring produced were dwarf.
Explain how it is possible for two tall parent plants to have this percentage of dwarf offspring.
A person who is homozygous for the sickle cell allele has a child with a person that is heterozygous.
What is the likelihood that the offspring would be homozygous for the sickle cell allele?
100 %
75 %
50\%
25 %
In guinea pigs, the allele for black fur is dominant and the allele for white fur is recessive.
A test cross can be used to determine the genotype of a guinea pig with black fur.
What would be the expected result of the test cross if the guinea pig with black fur was homozygous?
50\% black, 50\% white
25\% black, 75\% white
100\% black
100\% white
The plant Camellia japonica has flowers that can be white, red or a mixture of these two colours. When red-flowered plants are crossed with white-flowered plants, all the offspring plants have flowers with petals that are a mixture of red and white, as shown in Fig. 2.2.
Fig. 2.2
- The gene for petal colour in C. japonica is given the symbol P.
- The allele for white petals is given the symbol .
- The allele for red petals is given the symbol .
State the type of inheritance that is shown by petal colour in C. japonica.
Fig. 6.1 is a photomicrograph of a blood clot.
Fig. 6.1
There are four blood group phenotypes A, B, AB and O in humans.
State the two possible genotypes for a person who has the phenotype blood group A .
1
2
Fig. 3.1 shows a photomicrograph of human blood.
Fig. 3.1
Haemophilia is a sex-linked blood disorder. The blood of people with haemophilia takes longer to clot.
Fig. 3.3 is a pedigree diagram showing the inheritance of haemophilia.
Fig. 3.3
□ male with normal clotting time
male with haemophilia female with normal clotting time
- The allele for normal clotting time is represented by .
- The allele for haemophilia is represented by .
Describe what is meant by the term sex-linked characteristic.
Which statement describes red-green colour blindness?
It is an example of codominance.
It is more common in females than in males.
It only occurs in males.
The recessive allele is located on an X chromosome.
The eye is adapted for focusing on near and distant objects.
Fig. 3.1 shows the parts of the eye involved in focusing. The eye is focused on a distant object.
Fig. 3.1
Colour blindness can be caused by a mutation in a gene. The gene is located on the X chromosome.
Fig. 3.3 is a pedigree diagram of a family which has several people who are colour-blind.
Fig. 3.3
Use the information in Fig. 3.3 to complete the genetic diagram to show the probability of person 3 and person 4 having another child with colour blindness.
offspring
genotypes
offspring
phenotypes
probability of a child having colour blindness