Amistake by cellular machinery, or damage from an environmental agent such as radiation may produce a(n) which is a permanently altered segment of dna.

Mutated gene

A mistake by cellular machinery, or damage from an environmental agent such as radiation may produce a mutated gene which is a permanently altered segment of dna.  

A gene mutation is a perpetual change in the DNA sequence that forms a gene which makes the sequence different from what is present in most people. Gene mutations can be classified into; hereditary mutation (changes inherited from parents) and somatic mutation (changes caused by environmental factors such as ultraviolet radiation from the sun).

the second type of galaxy is called a barred spiral, which has a thing called a bar straddling the nucleus