Answer:
The behavior of chromosomes during meiosis and fertilization is responsible for most of the variation that arises in each generation. Three mechanisms contribute to genetic variation arising from sexual reproduction: independent assortment of chromosomes, crossing over, and random fertilization.
Genetic drift occurs when there is no random mating across a population. This causes a change in allelic frequency due to a random sampling of the population.
As the aboriginal population explored the earth, a small part of the population became geographically isolated either due to continental drift and climate changes. As the isolated population grew bigger, they established their own gene pool. This resulted a change in genotypic frequencies from that of the aboriginal population.
The planetary body that Spirit was designed to explore the wide ranges of soil and rocks for clues of the water activity on Mars. Spirit specifically landed at the Gusev Crater which was before, a possible lake in a giant crater.
A double layer of phospholipids
Because with sexual reproduction the offspring is getting Genetic material from both the mother and father but during asexual reproduction the offspring only gets genetic material from its one and only parent