Biology · Organisms and Populations · NEET
It is a POPULATION attribute, not an individual attribute. A single organism is simply male or female. Sex ratio (the proportion of males to females) can only be measured when you look at the whole group. NCERT states: 'An individual may have births and deaths, but a population has birth rates and death rates.' The same logic applies to sex ratio, so NEET commonly asks you to identify sex ratio as a population-level property.
It is expressed as a proportion or percentage of the two sexes. NCERT gives the example that a population may have a sex ratio such as 60 per cent females and 40 per cent males. So sex ratio is not a number of one individual; it is the relative share of males and females in the group.
They are completely different topics. Sex determination (from Genetics) is the mechanism, like XX/XY chromosomes, that decides whether ONE individual becomes male or female. Sex ratio (from Organisms and Populations) is an ecology term for the PROPORTION of males and females in a whole population. NEET can mix these two in tricky wording, so keep them separate.
NCERT lists these attributes that a population has but an individual does not: natality (birth rate), mortality (death rate), sex ratio, age distribution / age pyramid, and population density. A very common NEET question gives a list and asks which item is NOT a population attribute (the odd one is usually a community-level term like species interaction).
No. Sex ratio need not be 50:50. NCERT itself uses the example of 60 per cent females and 40 per cent males, showing that the two sexes can be present in unequal proportions in a real population.
Try the real previous-year questions from this chapter — each with the answer and a full solution.
Sex ratio is a population attribute that gives the proportion of males and females in a population, such as 60% females and 40% males as stated in NCERT.
Because it can only be defined for a group. A single individual has one sex, but the proportion of males to females appears only when you study the whole population.
No. Population density (N) is the size or number of individuals per unit area, while sex ratio is the proportion of males to females. Both are population attributes but they measure different things.
Sex ratio is covered in Class 12 Biology, Chapter 'Organisms and Populations', under population attributes, along with natality, mortality, age distribution and population density.
