In peas Dwarf d is recessive to tall D and yellow g cotyledo

In peas, Dwarf (d) is recessive to tall (D) and yellow (g) cotyledons is recessive to (G) cotyledons. A tall pea plant with yellow cotyledons was crossed with a dwarf pea plant green cotyledons. Write in the spaces provided the phenotypes and genotypes (with ration) in and F_2. If the F_1 in the cross above is used in a back-crossed to the dwarf parent: what will be he phenotypic and genotypic ratios resulting from this cross.

Solution

Answer 48a) According to the information given, tall (T) is dominant over dwarf (d) and green (G) is dominant over yellow (g) cotyledon.

In the following cross:
Parents: Tall plant with yellow cotyledon X dwarf plant with green cotyledon
   TTgg ttGG
Gametes: Tg tG
Offsprings: TtGg -------> F1 generation
   Tall plant with green cotyledon
Hence, F1 genotype: TtGg
F1 phenotype: Tall pea plant with green cotyledon

The F1 hybrid plants are allowed to self-fertilize. The cross will be as follows:
Parents: TtGg X TtGg
Gametes: TG, Tg, tG, tg TG, Tg, tG, tg
Offsprings:

In F2 generation:
Genotype Phenotype Number
TTGG Tall plant with green cotyledon 1/16
TTGg Tall plant with green cotyledon 2/16
TTgg Tall plant with yellow cotyledon 1/16
TtGG Tall plant with green cotyledon 2/16
TtGg Tall plant with green cotyledon 4/16
Ttgg Tall plant with yellow cotyledon 2/16
ttGG   Dwarf plant with green cotyledon 1/16
ttGg Dwarf plant with green cotyledon 2/16
ttgg Dwarf plant with yellow cotyledon 1/16

Hence, genotypic ratio: 1:2:1:2:4:2:1:2:1
Phenotypic ratio : 9:3:3:1

Answer 48b) The back cross is as follows:

Parents: F1 progeny X dwarf parents i.e recessive
   TtGg X ttgg
Gametes: TG, Tg, tG , tg tg
Offsprings:
Genotype Phenotype
TtGg Tall plant with green cotyledon   
Ttgg Tall plant with yellow cotyledon
ttGg Dwarf plant with green cotyledon
ttgg Dwarf plant with yellow cotyledon

In this case, the phenotypic and genotypic ratio is same i.e 1:1:1:1.

Gametes	TG	Tg	tG	tg
TG	TTGG	TTGg	TtGG	TtGg
Tg	TTGg	TTgg	TtGg	Ttgg
tG	TtGG	TtGg	ttGG	ttGg
tg	TtGg	Ttgg	ttGg	ttgg