New Genes as a Result from Changes and Mutations in Existing Genes

New genes can arise from changes and mutations within existing genes.
A mutation is a change in the DNA base sequence. They can occur naturally during DNA replication or can be induced by environmental factors such as radiation or certain chemicals.
Most mutations are harmful, but occasionally they can be beneficial. Beneficial mutations may provide a survival advantage, and organisms with these mutations are more likely to pass these genes onto their offspring.
For example, the development of antibiotic resistance in bacteria is an example of a beneficial mutation. A mutation in one bacteria that enables it to survive antibiotics will be passed onto future generations, resulting in a population of bacteria that are all resistant.
Mutation is the only source of new alleles in a population. Alleles are different versions of a gene, for example, the gene for eye colour has different alleles for blue eyes, brown eyes, etc.
Genetic variation within a species is very important for evolution. It is the raw material on which natural selection can work.
If a mutation results in a new gene that gives an organism a survival or reproductive advantage, then over time, this gene will become more common in the population. This process is known as natural selection, and it drives evolution.
Evolution is the gradual change in a species over time. Every species on Earth is a product of evolution. Over billions of years, simple, single-celled organisms have evolved into the complex variety of life we see today.
Different organisms can evolve similar features independently, usually because they’re adapting to similar environments or roles. This process is known as convergent evolution.
Conversely, divergent evolution occurs when a single species evolves into multiple species, often because they’re adapting to different environments or roles.

Understanding these topics will help you to grasp the fundamentals of variation and evolution, and provide a foundation for understanding more complex biological processes.