Final answer:
A pseudogene is very similar to a functional gene but cannot be expressed due to mutations. Pseudogenes can be identified using reverse genetics methodologies, and different mutations can impact gene expression, including dominant negative and recessive lethal mutations.
Step-by-step explanation:
A pseudogene is very similar to a functional gene but cannot be expressed because of mutations. A pseudogene may arise from duplication of a functional gene followed by the accumulation of mutations that lead to a loss of function. The presence of pseudogenes in a genome may be identified using reverse genetics methodologies that include comparing gene sequences and observing phenotypic consequences of gene deletions or mutations.
There are different types of mutations that can affect gene expression or activity, such as dominant negative mutations, which occur when the mutated gene product interferes with the normal function of the wild-type gene product. This interference often happens if both the normal protein and the mutated protein can interact with the same elements, but the mutated protein acts as a competitive inhibitor. An example of a phenotype that can result from such mutations is a dominant negative effect witnessed when a mutated allele of a tumor suppressor gene renders the other copy non-functional.
Some mutations can be recessive lethal, meaning that an allele can only cause lethality if it is present in two copies (homozygous form), while the heterozygous form of the allele may have a normal or altered non-lethal phenotype. Other mutations, like silent mutations, do not alter the amino acid sequence of the protein and hence do not typically affect the gene's function.