Question 4
(a) Explain briefly the following terms:
(i) gene;
(ii) hybrid;
(iii) trait. [6 marks]
(b) Two heterozygous yellow flowers are crossed. Using a genetic diagram, state the phenotypic and genotypic ratios of the first filial generation. [10 marks]
(c) State four transmittable characters in plants. [4 marks]
Observation
This was a popular question but poorly done.
Some candidates defined gene as a small part of a chromosome.
Some defined hybrid as an offspring from different species instead of same species.
For trait, some candidates stated that they are simple strands of genetic materials or children from parents instead of characters or features or factors which are transferrable from parents to offspring.
Some other candidates were able to explain the terms but could not relate parental genotype to gamete and to offspring. Many candidates did not show the X sign to show there is a cross. This made them lose
4 (c) was not well treated by some candidates that wrote colour, size, taste, instead of size of fruit/plant, colour of leaf/flower e.t.c.
The expected answers are:
(a) Explanation of terms
- Gene
Is a unit of heredity/genetic material; composed of DNA; located on the chromosome.
- Hybrid
Is an offspring; formed from a cross between parents that are genetically different; but of same species.
- Trait
Is a feature /character; that is possessed by an organism; and can be transferred from parent to offspring.
(c) Transmittable characters in plants
- Type of seed;
- Size of fruit;
- Colour of flower;
- Colour of leaf;
- Height of plant;
- Texture of seed coat;
- Size of plant;
- Leaf shape;