A homozygous tall, red flower plant was crossed with a homozygous dwarf, white flower plant. The F1 were selfed and 160 F2 plants were obtained. a.(i) Name ...
Question 1 Report
A homozygous tall, red flower plant was crossed with a homozygous dwarf, white flower plant. The F1 were selfed and 160 F2 plants were obtained.
a.(i) Name the type of genetic cross. [1 marks]
(ii) State one reason for the answer in 4(a)(i). [1 marks]
b.(i) What is evolution? [2 marks]
(ii) With the aid of a genetic diagram, state the phenotypic ratio of F2 generation. [13 marks]
(iii) Calculate the number of tall and white flowers that would be obtained in the F2 generation. [3 marks]
Answer Details
(a)(i) The cross is a dihybrid cross.
(a)(ii) It involves two pairs of contrasting characters, namely plant height (tall/dwarf) and flower colour (red/white).
(b)(i) Evolution is the gradual change in the inherited characteristics of a population over many generations, which may result in new forms or species.
(b)(ii) Genetic diagram
Let T represent tallness and t dwarfness; R represent red flowers and r white flowers. Tallness and red flower colour are dominant.
P generation: Tall, red plant (TTRR) × Dwarf, white plant (ttrr)
Gametes: TR × tr
F1 generation: all TtRr, tall and red.
Selfing of F1: TtRr × TtRr
Each F1 plant produces the four types of gametes: TR, Tr, tR and tr.
From the genetic diagram, the F2 phenotypic ratio is:
9 tall red : 3 tall white : 3 dwarf red : 1 dwarf white.
(b)(iii) Tall, white plants are represented by 3 out of 16 plants.
\[\text{Number of tall, white plants}=\frac{3}{16}\times160=30\]
Therefore, 30 tall, white-flowered plants would be obtained in the F2 generation.
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