An animal guinea pig having black colour is crossed with guinea pig having the same colour. They produced 100 offsprings, of which 75 were black and 25 were white.
Find out
(i) What is the possible genotype?
(ii) Which trait is dominant and which is recessive?
(iii) What is This cross called as and what is the ratio of f2 progeny obtained from this cross?
Answers
Answer:
(a) The possible genotype of the guinea pigs : BB, Bb & bb
(b) Black is dominant over white.
(c) Monohybrid cross ; 3:1
Explanation:
(a) Since the phenotypic ratio is 60:20 which means 3:1 , the parents have to be heterozygous. ,that is, Bb.
B is the dominant allele which is responsible for black color whether it is present in homozygous (BB) or heterozygous (Bb) condition and b is the recessive allele which express white color when present in homozygous (bb) condition.
So, Bb X Bb gives genotypes BB,Bb and bb which are the possible genotypes for guinea pig.
(b) The frequency of occurrence of dominant trait is higher then the recessive trait in a population .The phenotypic ratio is 3:1 where 3 indicates Black color and 1 indicates white color .Since black is present in more number of offsprings as compared to white ones, the dominant one is black color and recessive one is white color.
(c) It is involving cross between a single trait or character which is the color of guinea pig , therefore, it is a monohybrid cross.
Ratio of 60:20 gives the phenotypic ratio which is 3:1.
hope it helps you T_T
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