Select the correct answers to the questions from the given options. (Do not copy the questions, write the correct answer only.)
Ajay and Vijay are siblings. Ajay can roll his tongue while Vijay cannot. What is the genotype of their parents?
Topic: Monohybrid cross — working back to the parents
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Pick an option and check your answer. The full worked answer is below either way.
Answer
(d) Both the parents are heterozygous dominant..
Work BACKWARDS from the children, which is the skill this question tests.
Tongue-rolling is DOMINANT (T); non-rolling is RECESSIVE (t).
Vijay CANNOT roll, so Vijay must be tt — a recessive trait only shows when both alleles are recessive. He got one t from EACH parent, so BOTH parents must carry at least one t.
Ajay CAN roll, so at least one parent must carry T.
Therefore each parent has one T and one t — both are Tt, heterozygous dominant. Option (D).
Check by crossing Tt × Tt: the offspring are TT, Tt, Tt, tt — a 3:1 ratio, three rollers to one non-roller. Exactly what the family shows.
THE RULE TO CARRY AWAY: a child showing a RECESSIVE trait proves that BOTH parents carry the recessive allele, whatever the parents themselves look like. That one deduction answers most pedigree questions.
Both the parents are heterozygous dominant..