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]
a.(i) The type of genetic cross is a dihybrid cross, as the parents differ in two traits (tallness and flower color).
a.(ii) One reason for this answer is that the parents are homozygous for their respective traits, which allows for a clear separation of the traits in the offspring and enables the determination of the mode of inheritance.
b.(i) Evolution is the process of change in the heritable characteristics of populations over successive generations, which can result in the development of new species from existing ones.
b.(ii) The phenotypic ratio of the F2 generation can be determined using a Punnett square or a forked-line diagram. In this case, a Punnett square can be used to show the possible combinations of alleles in the F2 generation:
|
T |
t |
| R |
TR (Tall, Red) |
Tr (Tall, White) |
| r |
tr (Dwarf, Red) |
tr (Dwarf, White) |
The phenotypic ratio of the F2 generation is 9:3:3:1, which means that 9/16 of the offspring will be tall and red, 3/16 will be tall and white, 3/16 will be dwarf and red, and 1/16 will be dwarf and white.
b.(iii) To calculate the number of tall and white flowers in the F2 generation, we need to know the total number of offspring. In this case, the total number of F2 offspring is given as 160. From the phenotypic ratio, we know that 9/16 of the offspring will be tall, which is approximately 90 (9/16 x 160). Similarly, 3/16 of the offspring will be white, which is approximately 30 (3/16 x 160). Therefore, in the F2 generation, we would expect to obtain approximately 90 tall flowers and 30 white flowers.