Question 4
(a) In a particular plant species, yellow colour of flower (Y) is dominant over blue colour
of flower (y). A cross was carried out between a heterozygous yellow flower and a blue flower. With the aid of a genetic diagram, determine the:
(i) genotypes; and
(ii) phenotypes of the offspring. [9 marks]
(b) (i) What is organic evolution? [2 marks]
(ii) Name three scientists that contributed to the study of evolution. [3 marks]
(c) (i) State three reasons why some insects are considered to be social. [3 marks]
(ii) State three disadvantages associated with the mode of life of social insects.
[3 marks]
Observation
Some candidates were able to use the correct parental genotypes but did not put the X sign to represent a cross between the parents. This made them lose plenty marks. Some candidates did not also circle the gametes. Many of them could give the genotypes and phenotypes.
Some candidates could state organic evolution and some could only name only one scientist that contributed to the study of evolution but still lost marks to poor spelling.
Some candidates could not even give reasons why some insects are considered to be social; neither could they give disadvantages associated with the mode of life of social insects.
The expected answers are:
(a)(i) Genetic Diagram
Parental genotype Yy X yy 2x1 [2mark]
YYYYYyy
Gametes y y y [2marks]
Correct crossing(cc) 4x[2marks]
Genotypes Yy yy yy Yy 4x[2marks]
(ii) Phenotypes yellow blue blue yellow
Half yellow, half blue
OR
X |
Y |
y |
y |
Yy |
yy |
y |
Yy |
yy |
(b)(i) Organic Evolution
is the theory that more recent types of plants and animals have their origin in the other
pre-existing forms; and that the differences between ancestors and descendants are due
to modifications differences between ancestors and descendants are due to
modifications in successive generations.
Any 2x1[2mark]
(ii) Scientists that Contributed to the Study of Evolution
- Jean baptiste Lamarck/Lamarck
- Charles Darwin/Darwin
- Hugo de Vries
- Francesco Redi
Any 3x1[3marks]
(c)(i) Reasons Some Insects are Considered to be Social
- their activities are well coordinated;
- they live in groups/colonies/communities/castes;
- they have effective communication skills;
- community cares for the young cooperatively.
Any 3x1[3marks]
(ii) Disadvantages Associated with the Mode of Life of Social Insects
- frequent intra – specific competition for scarce resources;
- increased disease infections/outbreak of disease spread fast;
- increased predation of offspring by other predators;
- danger of being captured in large numbers.