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WAEC Biology 2019 Question 48

Question 48

Mendelian Inheritance

The cross between RrTt and rrtt where R is a gene for red colour and T for tallness will result in

  1. A.all the offspring being tall with red fruits.
  2. B.25 % tall with red fruits.
  3. C.50 % tall with red fruits.
  4. D.75 % tall with red fruits.
Show the answer and explanation

Answer: B (25 % tall with red fruits.)

Explanation

RrTt makes four kinds of gametes (RT, Rt, rT, rt) and rrtt makes only rt. The offspring are RrTt, Rrtt, rrTt and rrtt in equal numbers, so 1 in 4 (25%) is red and tall.