Directional selection.

Question

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Answer

Natural selection bringing about directional change without disrupting the balance is called directional selection.
In a population when more individuals acquire characters which are other than the mean character value, then it is called directional selection.
Natural selection usually acts to eliminate one of the extremes of the phenotypic range and favour the other. E.g. systematic elimination of homozygous recessives.
Directional selection operates for many generations, it results in an evolutionary trend within a population and shifting a peak in one direction.
E.g. Industrial melanism, DDT resistant mosquito, etc.

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Column I	Column II
(1) Acrosome	(a) Completion of IInd meiotic division of secondary oocyte
(2) Penetration of sperm into ovum	(b) Dissolution of zona pellucida
(3) Formation of fertilization membrane	(c) Secretion of Hyaluronidase
(4) Acrosin / Zona lysine	(d) Prevention of polyspermy

wBCs	%	Nucleus	Function
Neutrophils	70%		________________________
________	________	Twisted	Secretes heparin, histamine and serotonin
Fosinophils	________	________	Antihistamin / Antiallergic in function
Manocytes	3-5%	________	________________________
________	________	________	Responsible for cell mediated as well as humoral immunity

Respiratory capacities	Respiratory volumes
(1) Residual volume (RV)	(a) 500 ml
(2) Vital capacity (VC)	(b) 2000 – 3000 ml
(3) Tidal volume (TV)	(c) 1100 – 1200 ml
(4) Inspiratory reserve volume (IRV)	(d) 4100 – 4600 ml