Human Growth and Development / Unit 2 HGD 0162 worked example, 60 to 90 seconds
Inheritance Patterns
The idea
Inheritance follows several patterns. In dominant and recessive inheritance, one dominant allele is enough, while a recessive trait needs two copies. In incomplete dominance, the result is a blend, such as wavy hair. In codominance, both alleles show, as in blood type AB. In X-linked recessive inheritance, the allele sits on the X chromosome, so males are affected more often. Most traits, though, are polygenic, shaped by many genes together with the environment.
In practice
One family tree read five ways: brown and blue eyes, wavy hair, type AB blood, a colourblind son, and a range of heights.
Where people slip
Exam questions often describe a pattern and ask for its name. Look for the clue: a blend signals incomplete dominance, both traits showing signals codominance, and a trait that appears in sons through carrier mothers points to the X chromosome. When no single pattern fits, the answer is usually polygenic.
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