Mutations What is a Mutation A mutation is

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Mutations

Mutations

What is a Mutation? • A mutation is a change in an organism’s DNA

What is a Mutation? • A mutation is a change in an organism’s DNA – May or may not affect the phenotype

Mutations • Changes in the nucleotide sequence of DNA • May occur in somatic

Mutations • Changes in the nucleotide sequence of DNA • May occur in somatic (body cells)… aren’t passed to offspring – Cancer • May occur in gametes and be passed to offspring

Are Mutations Helpful or Harmful? • Mutations happen regularly and almost all are neutral

Are Mutations Helpful or Harmful? • Mutations happen regularly and almost all are neutral • Chemicals and UV radiation cause mutations (mutagens) • Many mutations are repaired by enzymes • Some mutations may improve an organism’s survival (beneficial)

Types of Mutations • Gene Mutations – Point mutation – Frameshift mutation • Chromosomal

Types of Mutations • Gene Mutations – Point mutation – Frameshift mutation • Chromosomal Mutations – Gene duplication – Translocation – Nondisjunction – Inversion – Deletion

Chromosome Mutations • May involve: – Changing the structure of a chromosome – The

Chromosome Mutations • May involve: – Changing the structure of a chromosome – The loss or gain of part of a chromosome (change in # or structure)

Chromosomal Mutations • Deletion – Due to breakage – A piece of a chromosome

Chromosomal Mutations • Deletion – Due to breakage – A piece of a chromosome is lost

Chromosomal Mutations • Inversion – part of a chromosome breaks off and reattaches in

Chromosomal Mutations • Inversion – part of a chromosome breaks off and reattaches in the opposite direction

Chromosomal Mutations • Gene duplication – Occurs when a gene sequence is repeated (copied

Chromosomal Mutations • Gene duplication – Occurs when a gene sequence is repeated (copied twice)

Chromosomal Mutations • Translocation – Nonhomologous chromosomes exchange segments of DNA – Like crossing

Chromosomal Mutations • Translocation – Nonhomologous chromosomes exchange segments of DNA – Like crossing over, but this is not a good thing!

Chromosomal Mutations • Nondisjunction – Chromosomes do not separate during meiosis (polyploidy) – Causes

Chromosomal Mutations • Nondisjunction – Chromosomes do not separate during meiosis (polyploidy) – Causes gamete to have too many or too few chromosomes • “Trisomy” • Ex: Down’s Syndrome

Chromosomal Mutations • Trisomies – Down’s Syndrome (trisomy 21) – Edward’s Syndrome (trisomy 18)

Chromosomal Mutations • Trisomies – Down’s Syndrome (trisomy 21) – Edward’s Syndrome (trisomy 18) • Strong physical defects – Patau Syndrome (trisomy 13) • polydactly • Sex Chromosomes – Turner’s Syndrome (XO) • Short stature, undeveloped bodies, infertility – Klinefelter’s Syndrome (XXY) • Tall, decreased testosterone, infertility – XYY Syndrome • Low effect on phenotype • Tall, sometimes reduced IQ

Genetic Disorders • We can use karyotypes to diagnose genetic disorders • The most

Genetic Disorders • We can use karyotypes to diagnose genetic disorders • The most common example is Down’s Syndrome • Caused by having three copies of the 21 st chromosome • Also known as Trisomy 21

Gene Mutations • Change in the nucleotide sequence of a gene • May only

Gene Mutations • Change in the nucleotide sequence of a gene • May only involve a single nucleotide • May be due to copying errors, chemicals, viruses, etc.

Point Mutation • Change of a single nucleotide • Also called substitution – Ex:

Point Mutation • Change of a single nucleotide • Also called substitution – Ex: GCGAT changed to GCGTT • Three types: – Nonsense (early stop codon) – Missense (changes the amino acid produced) – Silent (no effect on phenotype)

Point Mutation • Sickle cell disease is the result of one nucleotide substitution •

Point Mutation • Sickle cell disease is the result of one nucleotide substitution • Occurs in the hemoglobin gene

Frameshift Mutation • • A nucleotide is inserted or deleted Shift the entire sequence

Frameshift Mutation • • A nucleotide is inserted or deleted Shift the entire sequence of codons Also called insertion or deletion Proteins will be built incorrectly

Impact of Mutations • Chromosomal mutations affect many genes, so have a bigger impact

Impact of Mutations • Chromosomal mutations affect many genes, so have a bigger impact on an organism than single gene mutations • Gene mutations may or may not have an effect – Frameshift mutations are typically more severe – Point mutations may not effect the amino acid sequence at all • Mutations in body cells affect only the individual, while mutations in germ cells, or gametes, will also be passed on to offspring

Causes of Mutations • Replication errors • Mutagens: environmental causes of DNA mutation –

Causes of Mutations • Replication errors • Mutagens: environmental causes of DNA mutation – These include UV rays and chemicals

Cancer • Cancer occurs when cells are mutated so that they grow uncontrollably •

Cancer • Cancer occurs when cells are mutated so that they grow uncontrollably • They do not follow the normal cell cycle pattern of growth and division • Carcinogens: factors known to cause cancer

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Mutations and Genetic Engineering Mutations Types of mutationsMutations and Genetic Engineering Mutations Types of mutations
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