When parents $P_{1}$ and $P_{2}$ were crossed, $F_{2}$ progeny was produced with three fourth similar features in phenotype to $P_{2}$ and $F_{1}$ , and one fourth possessed contrasting traits. If the traits being considered here are for height with 'T' for tall and 't' for short. What will be the possible genotype of $P_{1}$ and one fourth of $F_{2}$ ?

tt and Tt

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Tt and tt

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Tt and Tt

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tt and tt

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Solution

The correct option is A Tt and tt
Gametes
Tt ( $P_{1}$ ; tall)
Tt ( $P_{2}$ ; tall) T t
T TT
(tall) Tt
(tall)
t Tt
(tall)
tt
(dwarf)
According to the question, 3/4th progeny was similar to $P_{2}$ and $F_{1}$ . Since $F_{2}$ progeny has two types of phenotypes in 3:1 ratio; both parents should carry one recessive allele to pass it to the 25% recessive progeny. To have 3:1 phenotypic ratio, parent genotype should be "Tt" because both "TT" parents give all "Tt (long) offspring, both "tt" parents give all "tt" offspring but "Tt" parents produce offspring with 3:1 ratio. This makes option D wrong. As we know that $F_{1}$ hybrids are heterozygous; here the 1/4 $F_{2}$ has contrasting character to $F_{1}$ and therefore should be dwarf with genotype "tt". The Tt genotype of 1/4 $F_{2}$ make option A and C wrong.
Therefore, the correct answer is option B.

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Gametes Tt ( $P_{1}$ ; tall) Tt ( $P_{2}$ ; tall)	T	t
T	TT (tall)	Tt (tall)
t	Tt (tall)	tt (dwarf)