In jimsonweed, purple flower (P) is dominant to white (p), and spiny pods (S) are dominant to smooth (s). A true-breeding plant with white flowers and spiny pods is crossed to a true-breeding plant with purple flowers and smooth pods. Determine the phenotype of:.
a) the F1 generation;
b) the F2 generation;
c) the progeny of a cross of the F1 plants back to the white, spiny parent; and
d) the progeny of a cross of the F1 back to the purple, smooth parent.

See attached image for detailed punnet squares and diagrams

a) F1 generation: Purple flower and spiny pods (PpSs) offsprings

b) F2 generation: Puple flower, spiny pods (9), Purple flower, smooth pods (3), White flower, spiny pods (3), white flower, smooth pods (1).

c) The progenies are: PpSS (4), PpSs (4), ppSS (4), and ppSs (4)

d) The progenies are: PPSs (4), PPss (4), PpSs (4), Ppss (4)

Explanation:

This question involves two distinct genes in jimsonweed; one coding for flower colour and the other for pod texture. The alleles for purple colour (P) and spiny pods (S) are dominant over the alleles of white flower (p) and smooth pods (s) in the two genes respectively.

A true-breeding plant with white flowers and spiny pods will have genotype: ppSS while a true-breeding plant with purple flowers and smooth pods will have genotype: PPss. In a cross between these two parents, the following combinations of gametes will be produced:

ppSS- pS, pS, pS and pS

PPss- Ps, Ps, Ps, PS

a) Hence, the F1 offsprings from this cross will possess a heterozygous genotype: PpSs, which is phenotypically purple-flowered and spiny-pod.

b) if the F1 offsprings are self-crossed i.e. PpSs × PpSs, gametes PS, Ps, pS, ps will be produced by each parent. These gametes will be used in a punnet square (see attached image) to produce the following F2 offsprings in proportion:

Purple flower, spinny pods (9)

Purple flower, smooth pods (3)

White flower, spiny pods (3)

White flower, smooth pods (1)

c) if the F1 offsprings are crossed back with the white, spiny parent i.e. PpSs × ppSS. The following progeny of offsprings will be produced: (see attached image)

PpSS (4),

PpSs (4),

ppSS (4), and

ppSs (4)

d) if the F1 offsprings are crossed back with the purple, smooth parent i.e. PpSs × PPss, the following progeny will be produced:

PPSs (4),

PPss (4),

PpSs (4), and

Ppss (4)

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