WAEC SSCE Biology
Study notes for Application of the principles of heredity in: Explanation of the terms linkage, sex — part of the WAEC SSCE Biology syllabus. 2 learning objectives with explanations and exam tips.
Linkage means genes located on the same chromosome tend to be inherited together. When genes are linked, they don't assort independently like Mendel described. For example, in Nigerian crops like cassava, if genes controlling leaf shape and stem colour sit close together on one chromosome, offspring will likely inherit both traits from the same parent rather than getting random combinations.
Sex-linked inheritance happens when genes sit on sex chromosomes, particularly the X chromosome. Males, having only one X chromosome, express recessive traits more easily than females who have two X chromosomes. Colour blindness in humans follows this pattern—more males show it than females because they need just one recessive gene.
Understanding these principles helps farmers predict crop traits and breeders select for desired characteristics in livestock. This knowledge improves agricultural productivity across Nigeria.
Linkage occurs when two genes sit close together on the same chromosome, so they inherit together rather than independently. Sex-linked traits are controlled by genes on the X chromosome, making them appear more frequently in males than females since males have only one X chromosome.
In Nigerian medical practice, understanding sex-linked inheritance helps doctors predict genetic diseases. For example, colour blindness appears more often in males because they need only one recessive allele on their single X chromosome to express the trait, while females need two copies.
Doctors use this knowledge when counselling families about inherited conditions like haemophilia. A carrier mother has a 50% chance of passing the condition to her sons. Genetic counsellors in Nigerian hospitals now routinely explain these patterns to help families make informed decisions about pregnancies and medical management.