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
