Consider the attached mechanistic pathway that governs the color of Truffula tre

Question

Consider the attached mechanistic pathway that governs the color of Truffula trees, as seen in the Lorax. Using either the Punnett Square or forked-line method, deduce the phenotypic ratio of the colors (pink or yellow) that result from the cross: (PPYY) x (ppyy). What phenotypic ratio would you expect for the F2 generation?

Pink Yellow (activates) inhibits) Transcriptional Transcriptional Activator Regulator Gene P or pp or yy Gene Y P and Y are functional alleles that activate the gene, however pp on w mask the effect of the other gene

Explanation / Answer

It is given that pp or yy mask the effect of other gene i.e. in case of presence of either pp or yy color gene would be masked.

It means presence of P or Y would be pink and presence of pp or yy or both makes it yellow.

If PPYY x ppyy

F1 progeny is PpYy (all Pink)

Selfing of PpYy results in four types of gametes i.e. PY, Py, pY, py

PPYY

Pink

PPYy

Pink

PpYY

Pink

PpYy

Pink

PPYy

Pink

PPyy

Yellow

PpYy

Pink

Ppyy

Yellow

PpYY

Pink

PpYy

Pink

ppYY

Yellow

ppYy

Yellow

PpYy

Pink

Ppyy

Yellow

ppYy

Yellow

ppyy

Yellow

Phenotypic Ratio of F2 progeny, pink : yellow flowers is 9:7

PY Py pY py PY

PPYY

Pink

PPYy

Pink

PpYY

Pink

PpYy

Pink

Py

PPYy

Pink

PPyy

Yellow

PpYy

Pink

Ppyy

Yellow

pY

PpYY

Pink

PpYy

Pink

ppYY

Yellow

ppYy

Yellow

py

PpYy

Pink

Ppyy

Yellow

ppYy

Yellow

ppyy

Yellow

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