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8 November, 01:51

In snapdragons, red flower color (R) is incompletely dominant to white (r), with heterozygous plants being pink. The broad-leaf allele (B) is incompletely dominant over narrow leaves (b), with the heterozygous plants having medium-width leaves. If a red-flowered, broad-leaved plant is crossed with a white-flowered, narrowleaved one, what will be the appearance of the F1 and F2 plants?

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  1. 8 November, 02:36
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    -All the F1 individuals will be pink with medium-width leaves.

    -The F2 plants can be:

    1/16 red flowers, broad leaves

    2/16 red flowers, medium-width leaves

    1/16 red flowers, narrow leaves

    2/16 pink flowers, broad leaves

    4/16 pink flowers, medium-width leaves

    2/16 pink flowers, narrow leaves

    1/16 white flowers, broad leaves

    2/16 white flowers, medium-width leaves

    1/16 white flowers, narrow leaves

    Explanation:

    When there is incomplete dominance, the heterozygous genotype produces a phenotype that's intermediate between the homozygous ones.

    In the case of flower color:

    RR: red Rr: pink rr: white

    In the case of leaves width:

    BB: broad Bb: medium-width bb: narrow

    A cross between a red-flowered, broad-leaved plant (RRBB) is crossed with a white-flowered, narrowleaved one (rrbb). The homozygous dominant plant only produces RB gametes, and the homozygous recessive plant only produces rb gametes.

    - - All the F1 individuals will be heterozygous for both genes (RrBb) and will therefore be pink with medium-width leaves.

    The F2 is a result of a F1xF1 cross. Each F1 individual produces the gametes RB, Rb, rB and rb. The possible genotypes and phenotypes arising from the combination of those gametes are:

    1/16 RRBB: red flowers, broad leaves

    2/16 RRbB: red flowers, medium-width leaves

    1/16 RRbb: red flowers, narrow leaves

    2/16 rRBB: pink flowers, broad leaves

    4/16 rRbB: pink flowers, medium-width leaves

    2/16 rRbb: pink flowers, narrow leaves

    1/16 rrBB: white flowers, broad leaves

    2/16 rrbB: white flowers, medium-width leaves

    1/16 rrbb: white flowers, narrow leaves
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