Tritanopia is which of these in terms of prevalence?
Answer: A
The S cone gene lies on chromosome seven rather than the X chromosome. Its inheritance is therefore autosomal and it affects both sexes equally. The S cone gene sits on chromosome seven. Its inheritance is autosomal rather than sex linked.
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Consider the following statements about the inheritance of colour vision deficiency.
1. Red green deficiency is inherited on the X chromosome.
2. It is therefore far commoner in men than in women.
3. Blue yellow deficiency is also carried on the X chromosome.
Answer: B
Correct answer: 1 and 2 only
Statements 1 and 2 go together: the L and M opsin genes are X-linked, so a man with one defective copy is affected while a woman needs two. Statement 3 is wrong - the S cone opsin gene lies on chromosome 7, so blue yellow deficiency is autosomal, rare, and affects the sexes equally.
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Assertion (A): Women are far less often affected by red green deficiency than men.
Reason (R): The relevant genes lie on the X chromosome, of which women carry two.
Answer: C
Both are true and the reason gives the genetics, and a normal allele on either chromosome suffices. Women may nonetheless be carriers of the condition. Two X chromosomes provide a spare allele. A normal allele on either one suffices.
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Some women are described as tetrachromats because they may possess
Answer: D
Correct answer: four distinct cone photopigments rather than three
A woman carrying different L or M gene variants on her two X chromosomes may express both, giving four cone types instead of three. Whether this yields genuinely finer discrimination depends on the visual system making use of the extra signal, and the evidence suggests only a minority of such carriers do.
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State whether the following is true or false.
Possessing four cone photopigments necessarily gives superior colour discrimination.
Answer: A
The visual pathway must also be able to exploit the extra signal. Evidence for enhanced discrimination in such individuals remains limited. The pathway must exploit the extra signal. Expression alone guarantees nothing at all.
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Colour vision screening is required for colour matching operatives because
Answer: B
Correct answer: a deficient observer may accept a match a normal observer rejects
A person with a colour deficiency sees the world perfectly well but confuses certain pairs, and those confusions are exactly where a metameric mismatch would show. Passing a batch that most customers will see as wrong is the commercial risk, which is why colour matchers are screened and periodically retested.
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Assertion (A): Visual colour assessment should not rely on a single observer.
Reason (R): Normal observers vary measurably in their colour matching functions.
Answer: C
Both are true and the reason gives the reason, and a panel averages out that variation. Instrumental measurement removes the observer variable entirely. A panel averages out the residual variation. One observer is never sufficient on its own.
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Consider the following statements about observers in industry.
1. Screening removes observers with a colour vision deficiency.
2. A panel of observers averages out normal variation.
3. Screened observers all give identical colour judgements.
Answer: D
The first two are correct and are standard practice. The third is not so, since normal observers still differ measurably from one another. Screening removes deficiency but not variation. Normal observers still differ from one another.
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Instrumental colour measurement removes observer variability but
Answer: A
Correct answer: still relies on an assumed standard observer throughout
A spectrophotometer measures reflectance, which is physics; converting that to tristimulus values requires weighting by an illuminant and a set of observer functions, which is a choice. The instrument removes the variability between individual people but replaces them with a single assumed average that no real observer exactly matches.
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Assertion (A): Two samples measuring identically may still look different to a particular observer.
Reason (R): The calculation uses a standard observer rather than the individual concerned.
Answer: B
Both are true and the reason gives the gap, and observer metamerism is the mechanism. Instrumental and visual assessment therefore complement one another. Neither replaces the other in practice. Instrument and eye answer different questions.
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