Study the given table and answer the following questions: Parents: ...

Question

Study the given table and answer the following questions:

Parents: A pea plant with red flowers was crossed with a pea plant with white flowers.

$F_1$: 30 seeds were sown and all bore plants with red flowers.

$F_2$: 44 seeds were sown, 33 plants bore red flowers and 11 plants bore white flowers.

(a) Depict the information given in the table in the form of a cross.

(b) Deduce the $F_2$ phenotypic ratio and the genotypic (genetic makeup) ratio.

Accepted Answer

Step 1: Assign the symbols. Since all $F_1$ plants are red, red is the DOMINANT trait (R) and white is the RECESSIVE trait (r).

(a) THE CROSS:

Parents: RR (red) $\times$ rr (white)

Gametes: R r

$F_1$ generation: All Rr - red flowers (100% red)

Selfing $F_1$: Rr $\times$ Rr

Gametes: R, r and R, r

Punnett square:

R r

R | RR | Rr

r | Rr | rr

$F_2$: RR, Rr, Rr, rr

(b) RATIOS IN $F_2$:

Phenotypic ratio (external appearance) = 3 red : 1 white.

Check with the data: 33 red : 11 white $= 3 : 1$. It matches.

Genotypic ratio (genetic makeup) = 1 RR : 2 Rr : 1 rr.

Conclusion: This is a monohybrid cross which confirms Mendel's law of dominance and law of segregation.