Heredity

In an asexually reproducing species, a trait that is found in a larger part of the population is more likely to have arisen earlier, because it had more time to be passed on to many descendants. Since trait B is present in 60% of the population, while trait A is present in only 10%, B is likely to have arisen earlier.

Variations promote survival because some variations give an individual advantage in a particular environment. If the environment changes, individuals with favourable variations are more likely to survive and reproduce. For example, bacteria that can withstand heat survive better during a heat wave. So, variations increase the chance that at least some members of a species will survive environmental change.

Mendel crossed plants with contrasting traits, such as tall and short pea plants. In the F1 generation, all plants were tall and no halfway height appeared. This showed that one trait was expressed over the other. When the F1 plants were self-pollinated, the F2 generation contained both tall and short plants, showing that the short trait had not disappeared but was only hidden in F1. Thus, the expressed trait is dominant, and the hidden one is recessive.

Mendel showed independent inheritance by crossing pea plants differing in two traits at the same time, such as seed shape and seed colour. In the F2 generation, besides the parental combinations, new combinations also appeared, such as tall with wrinkled seeds and short with round seeds. This means the traits for shape and colour were inherited independently and could recombine in different ways.

No, this is not enough to decide whether blood group A or O is dominant. The reason is that a person with blood group A can have a genotype that still carries an allele for O. Since the father with blood group A and the mother with blood group O produced a daughter with blood group O, the A parent must have contributed an O allele. This shows only that A is not always expressed, but to decide dominance we would need more information and more crosses.