1.A race of inbred plant has a mean petal length of 12 mm, a second race from another location has the same meant petal length. when the two races are crossed, the F1 also has the mean petal length of 12mm. however the F2 generation derived from crossing the F1 to one another shows a very wide spread in plant length. About 3 out of 770 have a length as small as 8 mm. and about 3 out of 770 have a length of 16 mm. How many allelic pairs seem to be involved in the different petal length? How much does each effective allele contribute to the length of petal?

parasites can detrimentally affect their host, but also must not allow their host to die before they can complete their life cycle. some parasites have complex life cycles with many different hosts, and have had to find ways of persisting in many different environments during the change from one host to another. ectoparasites live outside the body of the host, and can more easily  disperse, but are  more exposed to predators, parasites, parasitoids. endoparasites live inside the body of the host, and are therefore protected from the outside environment. but they can be  attacked by the host's immune system. they have therefore developed  mechanisms for dispersal such as  complex life cycles.

stratosphere: as the altitude increases, the air temperature increases. the stratosphere has a layer of ozone, called the ozone layer. this layer absorbs most of the ultraviolet radiation from sunlight. this results in the stratosphere being warmer.

the element that provides strength to the exoskeletons of clams and oysters is phosphorus. this is so because calcium carbonate is the main component in the shells.

explanation: