Genes and mutations

What are genes?• A molecular unit of heredity• The name for stretches of DNA and RNA that code

for a specific protein (which has a specific function in the organism)

Genes: Coding regions• Your DNA has coding and non-coding regions• Genes are the proteins that are made from the

coding regions.

Genes: Inheritance• Every person has two copies of each gene – one

inherited from each parent• Most genes are the same in all humans – only a

small number are different (less than 1%)

Genes: mutations• Genes can be mutated when the DNA is mutated• There are two types of DNA mutations:

• Point Mutations: a change in a single base pair • Result: changing a single nitrogen base can

change the entire structure of a protein (due to change in one amino acid)

• Frameshift Mutation: single base is added or deleted from DNA• Result: every amino acid after shift is changed

Genes: Mutations• Example of a Point Mutation:

THE DOG BIT THE CAT

THE DOG BIT THE CAR

…changing a single letter changes the meaning

Genes: Mutations• Example of a Frameshift Mutation

(deletion):

THE DOG BIT THE CAT

THE DOB ITT HEC AT

…deleting a single letter changes the reading of everything down the line from the mutation.

Chromosomal mutations

• Deletions: part of chromosome is left out

Chromosomal mutations

• Insertions: duplication of genes in the same chromosome

Chromosomal mutations

• Inversions: part breaks out and reinserts itself backwards

Chromosomal mutations

• Translocations: part breaks off and is added into a different chromosome

Chromosomal mutations

• Non-Disjunction: failure of homologous chromosomes to separate properly during meiosis

What causes mutations?

• Random events• Environmental agents (X-rays, UV light,

radioactivity, etc.)

Results of mutations• If it occurs in gametes (sex) cells:• Can cause birth defects, abortion, or no change• Few are passed on to next generation because

zygote usually dies

• If it occurs in somatic (body) cells:• Can lead to cancer, or no change