1.

Question : Describe the inheritance of human skin colour.

Answer»

Solution :(1) The inheritance of skincolour in humans is polygenic .
(2) DavenportandDavenportstudied the inheritance of skincolour of offspring after a marriagebetween a black and a white .
(3) The offsprings derived from this marriage show intermediate skin colour. Such individuals withintermediate skin colour are called mulattoes.
(4) When there is a marriage between two mulattoes, all shades of colour are observed in their offsprings in the ratio of
1 : 6: 15 : 20 : 15 :6 :1
(5) From the above results it is obvious that skin colour in humans is controlled by there pairs of genes, viz, Aa , Bb and Cc.
(6) The colour of skinin human beings is determined by the presence of pigment called melanin.
(7) The synthesis of melanin in the skin is controlled by dominant genes which are additive in their effect.
(8)Greater the number of dominant genes greater is the amountof melanin synthesized.
(9) The black has the genotype AABBCC and the albino has the genotype aabbcc.
(10) The offspring (mulatto)possesses the heterozygous geno TYPE AaBbCc.
(11) . Mulattoes produce eight different types of gametes and in `F_(2)`generation there are SIXTY four combinations. Owing to the cumnlativeof each dominant gene the results are as shown below :
(i) Pure black -1 /64(6 dominant genes)
(ii) Black ( LESS dark ) - 6/64(5 dominantgenes )
(iii)Lesser black or brown -15/64(4 dominantgenes)
(iv) Mulatto (Intermediate - Sanwla ) 20/64 (3 dominant genes)
(v) Fair 15/64 (2 dominant genes)
(vi)Very fair 6/64 (1 dominantgene)
(vii) Pure white(albino) 1/64(No dominantgene)


Discussion

No Comment Found

Related InterviewSolutions