2019 WAEC Biology Theory A homozygous tall, red flower plant was crossed with a homozygous dwarf, white flower plant....

WAEC 2019

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]

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Explanation

a. (i) Type of genetic cross: Dihybrid
(ii) Reason for answer: Two characters are involved in the cross/involves two characters separable in inheritance.

b. (i) Phenotype of F1: Tall and Red.
(ii) Genetic Diagram
   Let T represent the gene for Tallness;
   t represent the gene for Dwarfism;
   R represent the gene for Red;
   r represent the gene for White.

Parental genotype TtRr X TtRr

X	TR	Tr	tR	tr
TR	TTRR Tall Red	TTRr Tall Red	TtRR Tall Red	TtRr Tall Red
Tr	TTRr Tall Red	TTrr Tall White	TtRr Tall Red	Ttrr Tall White
tR	TtRR Tall Red	TtRr Tall Red	ttRR Dwarf Red	ttRr Dwarf Red
tr	TtRr Tall Red	Ttrr Tall White	ttRR Dwarf Red	ttrr Dwarf White

Crosses of parental genotypes
   Tall and Red - 9
   Tall and White - 3
   Dwarf and Red -   3
   Dwarf and White   - 1
   Parental genotype
   Parental gametes (TR, Tr, tR, tr) shown
   Correct Crosses of parental gamete
   Phenotypic ratio   9:3:3:1

(iii) Calculation of Tall and White flowers in F2
(3/16) x (160/1) = 30

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