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In the cross between smooth seed coat and wrinkled seed coat, all F1 generation seeds had a smooth coat. Determine the genotypes of the F1 generation and the F2 genotypic ratio.

Biology

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  1. Determine dominance and assign alleles.

    In the cross between smooth seed coat and wrinkled seed coat, all F1_1 generation seeds had a smooth coat. This indicates that the smooth seed coat trait is dominant over the wrinkled seed coat trait.

    Let 'S' represent the dominant allele for smooth seed coat.
    Let 's' represent the recessive allele for wrinkled seed coat.

  2. Determine the genotypes of the parental (P) generation.

    Since all F1_1 offspring are smooth, the smooth parent must be homozygous dominant (SS) and the wrinkled parent must be homozygous recessive (ss).
    Parental genotypes: Smooth (SS) ×\times Wrinkled (ss)

    a) Work out the genotypes of the F1_1 generation.
    To find the F1_1 genotypes, we cross the parental genotypes:

    P: SS×ss\text{P: SS} \times \text{ss}

    Gametes: S from SS, s from ss

    F1:Ss\text{F}_1: \text{Ss}

    All F1_1 individuals are heterozygous (Ss) and will express the dominant smooth phenotype.

    The genotypes of the F1_1 generation are: Ss\boxed{\text{Ss}}

    b) From the information above, work out the following for the F2_2 generation:
    The F1_1 generation (Ss) was selfed. This means we cross Ss ×\times Ss.

  3. Perform the F1_1 self-cross (Ss ×\times Ss).

    We can use a Punnett square:

    Ss
    SSSSs
    sSsss

    b) (i) Genotypic ratio for the F2_2 generation.
    From the Punnett square, the genotypes are SS, Ss, and ss.
    The ratio of these genotypes is:

    SS : Ss : ss=1:2:1\text{SS : Ss : ss} = 1 : 2 : 1

    The genotypic ratio is: 1:2:1\boxed{1:2:1}

    b) (ii) The total number of wrinkled seeds in the F2_2 generation.
    From the Punnett square, the genotype 'ss' corresponds to the wrinkled seed phenotype.
    The proportion of 'ss' individuals in the F2_2 generation is 14\frac{1}{4}.
    The total number of F2_2 generation individuals is 7324.

    Number of wrinkled seeds = (Proportion of wrinkled seeds) ×\times (Total F2_2 individuals)

    Number of wrinkled seeds=14×7324\text{Number of wrinkled seeds} = \frac{1}{4} \times 7324 Number of wrinkled seeds=1831\text{Number of wrinkled seeds} = 1831

    The total number of wrinkled seeds is: 1831\boxed{1831}

    b) (iii) Phenotypic ratio for the F2_2 generation.
    From the Punnett square:

    • SS and Ss genotypes result in the smooth phenotype (dominant).
    • ss genotype results in the wrinkled phenotype (recessive).

    So, the phenotypes are Smooth (SS, Ss) and Wrinkled (ss).
    The ratio of these phenotypes is:

    Smooth : Wrinkled=(1+2):1=3:1\text{Smooth : Wrinkled} = (1+2) : 1 = 3 : 1

    The phenotypic ratio is: 3:1\boxed{3:1}

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