Help with gene duplication and divergence.Watch
Also, How does gene duplication promote divergence? Explain how the goblin family is an example of duplication and divergence, and explain how the diversity of goblin genes is necessary for humans.
On the other hand, globin genes are a good example of a gene family which has arisen from the duplication and divergence of an ancestral globin gene. This video is quite a concise introduction to the concept. Duplication facilitates divergence because one copy of the gene can retain its original function, thus allowing the duplicated version some freedom to vary. In the case of the human haemoglobins, for example, adult haemoglobin usually consists of tetramers made up of the gene products haemoglobin alpha and haemoglobin beta (just two variants) because these optimise gas exchange under most normal conditions. However, the ancestral globin gene has also duplicated and diverged so extensively that something like 200 variants of human haemoglobins are known. Most variants are unhelpful or pathological, but some are highly adaptive, as they produce haemoglobins which function better in certain conditions. Hence, the embryo uses a haemoglobin variant (haemoglobin gamma) produced by a variant gene. This gene is down-regulated later in life, in favour of the variants that produce adult haemoglobins.