A: Due to bottle nect effect, among the survivors, certain alleles may be over-represented, some may be under-represented and some alleles may be totally eliminated.
R: The path extinction of a species cannot be reversed due to bottle neck effect.

Comprehension: Read the passage and answer the questions that follow. The term 'dietary fibres' refers collectively to indigestible carbohydrates present in plant foods. The importance of these dietary fibres came into the picture when it was observed that the people taking a diet rich in these fibres had low incidence of coronary heart disease, irritable bowel syndrome, dental caries and gall stones. The foodstuffs rich in these dietary fibres are cereals and grains, legumes, fruits with seeds, citrus fruits, carrots, cabbage, green leafy vegetables, apples, melons, peaches, pears etc. These dietary fibres are not digested by the enzymes of the stomach and the small intestine. They have the property of holding water and because of it, these get swollen and behave like a sponge as these pass through the gastrointestinal tract. The fibres add bulk to the diet and increase transit time in the gut and decrease the time of release of ingested food in the colon. These fibres hold water so the stools are soft bulky and readily eliminated. In recent years, it has been considered essential to have some amount of fibres in the diet. Their beneficial effects lie in preventing heart disease and decreasing cholesterol level. The fibres like gum and pectin are reported to decrease post prandial (after meals) glucose level in blood. They are also recommended for the management of certain types of diabetes. The fibres increase motility of the small intestine and the colon and so there is less time for exposure of the mucos a to harmful toxic substances. Therefore, there is a less desire to eat and the energy intake can be maintained within the range of requirement. This phenomenon helps in keeping a check on obesity. The dietary fibres may have some adverse effects on nutrition by binding some trace metals like calcium, magnesium, phosphorus, zinc and others and therefore preventing their proper absorption. This may pose a possibility of nutritional deficiency especially when diets contain marginal levels of mineral elements. This may put constraints on increasing dietary fibres. It is suggested that an intake of 40 gram dietary fibres per day is desirable. SubQuestion No : 21 The dietary fibres behave like a sponge because they: