In the f1 generation of a mendelian cross,
a. only the dominant trait is visible.
b. only the recessive trait is visible.
c. neither the dominant nor recessive trait is visible.
d. both the dominant and recessive traits are visible.

A. only the dominant trait is visible.

Explanation:

In the F1 generation of a Mendelian cross only dominant trait is visible. Mendel got all heterozygous individuals in the F1 generation i.e. individuals having one dominant and one recessive allele for a particular trait and the presence of one dominant allele masked the expression of recessive allele for that trait.

For example, when he made a cross between parents which were homozygous for round seeds (RR) and wrinkled seeds (rr), in F1 generation he got all the plants which had round seeds with Rr genotype because round seeds are dominant over wrinkled seeds.

The cross is shown as under:

Parental                 RR     x      rr

F1                         Rr    Rr    Rr    Rr

All the off springs in F1 generation have heterozygous genotype which is Rr and they all will have round seeds i.e. they all will display dominant trait not recessive. In all of these individuals, R allele will mask the expression of r allele so not even a single off spring will have recessive trait which is wrinkled seeds.

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e) all of the above