Give scientific reasons for the following statements:
Colour blindness is more common in men than in women.
Topic: Colour blindness in males
Answer
Because the gene for colour blindness is RECESSIVE and is carried on the X CHROMOSOME. A male is XY, so a SINGLE defective X is enough to produce the condition — the Y carries no corresponding allele to mask it. A female is XX and would need a defective X from BOTH parents, which is far rarer; with only one she is a CARRIER but has normal vision.
The answer must name the X CHROMOSOME and explain the ASYMMETRY between XY and XX — that is the whole reason.
This pattern is called SEX-LINKED or X-LINKED INHERITANCE, and naming it is worth doing.
HAEMOPHILIA follows exactly the same pattern and for the same reason, which is why the two are almost always asked together.
Contrast ALBINISM, which is also recessive but AUTOSOMAL — carried on an ordinary chromosome — and therefore affects both sexes equally.