Antibodies are produced when the body is exposed to a pathogen. Antibody production is a function of the specific immunity arm of the immune system.
During the first encounter with a pathogen, antibody production against that pathogen is a bit slow and not very vigorous. However, memory of that pathogen is kept in memory cell which are a type of lymphocyte.
On a second encounter with the same type of pathogen, the immune system specifically remembers the pathogen and the response this time round is faster, very vigorous, specific and very effective.
Vaccines follow this principle, making good use of immune memory.
Males tend to determine the sex of the baby depending on whether sperm is carrying and X or Y chromosome. An X chromosome combines with a mothers X chromosome to make XX (Girl). A Y chromosome from a male will combine with a mothers X chromosome to make an XY (Boy).
Males always pass on the Y chromosome
Answer:
Darwin's theory of natural selection lacked the physical proof of the intermittent species as suggested by him. The fossils of such species had not been discovered by the time he wrote his book 'Origin of species'. In order to defend his theory, he pointed out the non-reliability on fossils.
Explanation:
The field of geology was just evolving at the time Darwin wrote his book, and no fossils supporting his theory has been discovered yet. He defended his theory by saying that the fossils cannot be depended on for the proof of evolution as the the process of fossilization depends on many factors, and the available fossils are very rare. The irregularities in the geological records, also suggested that the fossil records are not perfect.
Defending his theory, he shows how, if available. the fossil records can support his theory. The fossils should show the features of both the extinct (parent species ) species and the present species, as the species present in today's world have evolved from the ones that existed long before them through the process of natural selection.
The discovery of the Archaeopteryx in 1861 supported his theory and the process of evolution as it showed the features of both the reptiles and birds.
