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]
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.
OR
Parental genotype TtRr X TtRr
| X | TR | Tr | tR | tr |
| TR |
TTRR |
TTRr |
TtRR |
TtRr |
| Tr | TTRr Tall Red |
TTrr Tall White |
TtRr Tall Red |
Ttrr |
| tR | TtRR Tall Red |
TtRr Tall Red |
|
|
| tr | TtRr Tall Red |
Ttrr Tall White |
ttRR Dwarf Red |
ttrr |
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