In Mendel's experiments, a trait that disappeared in the F1 generation but reappeared in the F2 generation was always a

A trait that disappeared in the F1 generation but reappeared in the F2 generation was always a RECESSIVE TRAIT.

Explanation:

The basic laws of genetics were laid down by an Australian monk in 1866, Gregor Mendel. From the results of his experiment, Mendel came to certain conclusions which are referred to as the Mendel's Laws of Heredity one of which includes the Law of Segregation of genes.

The Law of Segregation states that:

--> the hereditary characters of an organism are determined by genes

--> a gene for a character may have alternative forms ( alleles) which express the character in different ways;

--> if a diploid organism has two different alleles ( heterozygous) for a character, one allele may be dominant, dictating the expression of the character to the complete exclusion of the other ( the recessive allele).

Furthermore, Mendel's experiments can be proven by the study of a single- factor inheritance pattern. This is achieved by crossing a pure stock of white- flowered pea plants and red - flowered ones. The offspring of this cross are all red flowered pea plants. They form the F1 GENERATION.

Since only red flower colour is seen in the F1 generation, we say the the red flower form of the character is dominant. White colour, which does not show up in the F1 generation, but reappear in F2 GENERATION when F1 GENERATION is crossed, is said to be the recessive form of the character.

Therefore, this implies that the recessive traits can skip a generation to appear in future generations according to Mendel's experiments.

it has one origin of replication, but it proceeds in two directions - d)

it would be c. xylem.