Q4. State the biological species concept and name the scientist who introduced it.
Ernst Mayr: a species is a set of populations whose members breed, or could breed, with one another and which are cut off reproductively from all other populations (beyond the NCERT text).
Q5. Give one pre-zygotic and one post-zygotic isolating mechanism, with an example of the second.
Pre-zygotic: seasonal isolation, breeding at different times of the year (also habitat, behavioural, mechanical or gametic isolation). Post-zygotic: hybrid sterility, as in the mule (beyond the NCERT text).
Q6. Which three of Stebbins’ five factors supply variation, and which two shape it?
Gene mutation, changes in chromosome structure and number, and genetic recombination supply variation; natural selection and reproductive isolation shape it (beyond the NCERT text).
Q7. How does allopatric speciation differ from sympatric speciation?
In allopatric speciation a geographic barrier separates part of a population before it becomes a new species; in sympatric speciation the new species arises in the same area as its parent species, as through polyploidy in plants (beyond the NCERT text).
Q8. Which three scientists founded theoretical population genetics?
R. A. Fisher, J. B. S. Haldane and Sewall Wright (beyond the NCERT text).