Inheritance (Cambridge O Level Biology)

The four o’clock plant, Mirabilis jalapa, can have flowers of three different colours as shown in Fig. 1.

Fig .1

A student crossed some red-flowered plants with some yellow-flowered plants (cross 1).

She collected the seeds and grew them. All of the plants that grew from these seeds had orange flowers.

Complete the genetic diagram to explain the result of cross 1.

The student then carried out three further crosses as shown in Table 1.

Table 1

Complete the table by writing in the genotypes of the offspring of crosses 2, 3 and 4, using the same symbols as in the genetic diagram in (a).

Flower colour in M. jalapa is not an example of the inheritance of dominant and recessive alleles.

Explain how the results of the crosses show that these alleles for flower colour are not dominant or recessive. 

Fig. 1 shows the sequence of events that occur in sexual reproduction.

Fig. 1

State the name of cell T in Fig. 1.

[1]

(ii)

State the name of the process that takes place at S to form cell T in Fig. 1.

[1]

(iii)

State where in the human body process S takes place.

[1]

Some humans have the ability to roll their tongues and some cannot roll their tongues.

This characteristic is controlled by genes.

Fig. 2 shows two boys: boy A cannot roll his tongue and boy B can roll his tongue.

Fig. 2

The allele for tongue rolling (T) is dominant to the allele for non-tongue rolling (t).

Fig. 3 shows a family tree for this characteristic. Individual 1 and his partner are both heterozygous for tongue rolling.

Fig. 3

Table 1

[3]

Individual 2 in Fig. 3 is heterozygous for tongue rolling. He marries a woman who cannot roll her tongue.

State all of the possible genotypes of their children and predict the ratio of phenotypes for their children.

[2]

One parent of a child has blood group B and the other parent has blood group A. The child has blood group O.

The parents decide to have another child.

Complete the genetic diagram in Fig. 3.1 to show the possible blood groups for the second child of these parents.

Some people inherit a condition which prevents the production of the dark pigment melanin in their choroid and skin cells. The gene involved has two alleles, A (dominant)  and a (recessive).

Only people with two recessive alleles have this condition.

Two people, each with a heterozygous genotype, have children together.

[4]