If a trait A exists in 10% of a population of an asexually reproducing species and a trait B exists in 60% of the same population, which trait is likely to have arisen earlier? 

Sol.       Trait B is likely to have arisen earlier because it is present in a larger portion of the population.

Variations take place in response to the changes in the environment. Such variations enable a species to cope with the new changes. Thus, variations help a species in survival.

Depending on the nature of variations different individuals would have difference kinds of advantage to adjust in particular habitat. Variation help the individual to have different traits that may develop the organisms more tolerable.

In Monohybrid cross of Mendel between tall and dwarf pea plant, all progeny in F1 generation are tall , one  of  the  pair  of  traits  did  not  appear  in  the  F1 generation and in F2 generation, 75% of pea plants are tall but 25% are dwarf. This shows that traits are dominant or recessive.

During dihybrid cross by Mendel, it was observed that when two pairs of traits were considered; each trait expressed independent of the other. 

When a pea plant having round green seeds is crossed with a pea plant having wrinkled yellow seeds in F1 generation all the plants have round yellow seeds. But in F2 generation two new traits that is round yellow and wrinkled green appear. This
shows that traits are inherited independently. 
Mendel was able to propose the Law of Independent Assortment which says about independent inheritance of traits.

No. This information is not sufficient to determine which of the traits - blood group A or O - is dominant. This is because we do not know about the blood group of all the progeny.

Blood group A can be genotypically AA or AO. Hence, the information is incomplete to draw any such conclusion.