Mutations A change in the genetic code DNA

Mutations A change in the genetic code (DNA)

• Causes a change in the amino acid and therefore the protein that is made.

Mutations can happen: • when cells make mistakes in copying DNA • when cells are exposed to mutagens such as • radiation - X-rays, sun • chemicals - cigarette smoke, pollutants • viruses - HPV

MUTATIONS can be: Beneficial – • a source of genetic variation • can help an organism survive and reproduce • provide a way for species to change over time Harmful – • Causing illness • Genetic disorders Cystic fibrosis

MUTATIONS can occur: In body cells – – Cause cancer – Kill cells – Make cells unable to function **BUT will NOT be passed on to offspring** In sex cells (gametes) – - can lead to the evolution of a species - can cause genetic disorders **Can be passed on to offspring**

• Worksheet here

There are three ways that DNA can be altered when a mutation (change in DNA sequence) occurs 1. Substitution – one base-pairs is replaced by another: Example: G to C or A to G C G T C 2. Insertion – one or more base pairs is added to a sequence: Example: CGATGG –– CGAATGG GCTACC GCTTACC 3. Deletion – one or more base pairs is lost from a sequence: Example: CGATGG –– CATGG GCTACC GTACC

There are 5 possible results of a mutation

1. Silent Mutations • When a base pair is substituted but the change still codes for the same amino acid in the sequence: • Example: TCT and TCC both code for the amino acid Serine

2. Missense: • When a base pair is substituted and the new codon codes for a different amino acid: • THE DOG BIT THE CAT • THE DOG BIT THE CAR Example: • TCT codes for Serine and CCT codes for Proline

m. RNA Protein Stop Replace G with A m. RNA Protein Stop

3. Nonsense • When a substitution results in the formation of a STOP codon before all of the codons have been read and translated by the ribosome. Example: • GTGGTCCGAAACACC –– GTGGTCTGAAACACC • Val-Pro-Asn-Thr Val-STOP

4. Codon Deletion or Insertion: • A whole new amino acid is added, or one is missing. Example: GTGGTCCGAAACACC –– GTGGTCTGCCGAAACACC Val-Pro-Asn-Thr Val-Cys-Pro-Asn-Thr

5. Frame Shift: – A mutation in which a single base is added or deleted from DNA – Causes nearly every amino acid after the mutation to be changed in the protein because it affects many codons • THE DOG BIT THE CAT • THE DOB ITT HEC AT (deletion of G) • THE DOG GBI TTH ECA T (addition of G) Example: GTG GTC CGA AAC ACC T – GTG GTC GAA ACA CCT Val-Pro-Asn-Thr Val-Glu-Thr-Pro

Frameshift Mutation m. RNA Protein Stop Deletion of U m. RNA Protein

• Let’s practice!

Genetic Disorder • is an illness caused by one or more abnormalities in the genome Examples of genetic disorders caused by mutations:

Phenylketonuria (PKU) CAUSE: ENZYME Mutation in gene for an ______ breaks down an ______ amino acid that _____ called phenylalanine X X MENTAL RETARDATION Build up causes ____________ http: //biology. clc. uc. edu/courses/bio 104/protein. htm

Phenylketonuria (PKU) ALL babies are ____ tested ____ for PKU before they leave the hospital. http: //labspace. open. ac. uk/file. php/2588/SK 195_6_002 i. jpg Treatment: LOW in phenylalanine to Need a diet ___________ extend life and _______ mental PREVENT retardation amino acid If phenylalanine is an _______, what type of foods should PKU patients avoid? PROTEINS ! _________

REAL WORLD LINK What does a can of Diet Coke have to do with human genetics? LOOK AT THE WARNING LABEL ! NUTRASWEET is made with phenylalanine _______

HUNTINGTON’S DISEASE CAUSE: DUPLICATION of an extra 40 -100 _______ CAG repeats at end of gene on chromosome 4 more repeats. . . the earlier it shows up The _______ and more _____ severe the symptoms. http: //www. healthsystem. virginia. edu/internet/huntdisease/images/cag. gif

HUNTINGTON’S DISEASE Huntington’s brain Middle age Appears at ______ Lose the ability to walk, talk, feed yourself, mental and other ____ functions 1 in 10, 000 people in U. S. have Huntington’s disease Normal brain http: //www. scielo. br/img/revistas/bjmbr/v 39 n 8/html/6233 i 01. htm

A person with Huntington’s disease 50% chance of has a _____ passing the disorder on to their offspring. Problem: Symptoms of disorder usually don’t show until ______ MIDDLE AGE. . . so you don’t know you have it until ____ AFTER you have had children.

HEMOPHILIA CAUSE: Mutation in genes for _________ Blood clotting proteins on X chromosome carried ______ Blood clotting proteins are missing so person with this disorder can’t stop bleeding when bleed to death from minor injured; can ________ cuts or suffer internal bleeding from bruises or bumps.

HEMOPHILIA Treatment: injections of normal clotting Need ______ proteins to stop bleeding More common in ______ males because it is _______ TWO recessive X-linked, but females with ______ hemophilia alleles will also show the trait. 1 in 10, 000 males has hemophilia

Hemophilia • Symptoms – Heavy bleeding from minor cuts, nosebleeds, monthly periods

Hemophilia • Causes – Defective gene located on the X chromosome • Men will have hemophilia if they have the affected X chromosome • Women will have hemophilia only if they have two affected X chromosomes

Hemophilia • Detection/Treatment – Doctor may give regular factor replacement directly into the bloodstream

Duchenne Muscular Dystrophy CAUSE: deletion in gene that codes for a muscle protein ________ Results in progressive weakening __________ and loss of skeletal muscle __________ http: //www. cadenhead. org/workbench/gems/jerry-lewis-telethon. jpg http: //www. tokyo-med. ac. jp/genet/chm/dei. gif

Duchenne Muscular Dystrophy (DMD) SYMPTOMS: 1 in 3000 male births Appears before age 5 Progressive muscle weakening Most in wheelchair by age 13 Eventually lethal

CYSTIC FIBROSIS CAUSE: Loss of 3 DNA bases in a gene for the protein Cl- ions _______ that transports _____ so salt balance is upset thick mucous Causes a build up of _________ in lungs and digestive organs Image from: BIOLOGY by Miller and Levine; Prentice Hall Publishing © 2006

CYSTIC FIBROSIS http: //learn. genetics. utah. edu/content/disorders/whataregd/cf/index. html

CYSTIC FIBROSIS Leads to: _____ and _____ respiratory digestive complications, increased susceptibility to infections; Salty skin is a symptom “_____” • • 30, 000 people in U. S. have cystic fibrosis 1 in 31 people are carriers

Cystic Fibrosis • Causes – Two recessive alleles for membrane protein that transports chloride ions – Chloride ions not pumped out of the cells causing too many sodium ions to enter • Result – Mucus becomes thick and accumulates in respiratory and digestive systems

Cystic Fibrosis • Detection/Treatment – Respiratory problems • Physical therapy • Breathing exercises • Modern antibiotics – Digestive problems • Capsules containing pancreatic digestive enzymes

Sickle-Cell Anemia • Symptoms – Severe pain due to obstructed blood vessels – Anemia caused by the fragility of red blood cells

Sickle-Cell Anemia • Causes – Homozygous condition – Formation of abnormal hemoglobin – Sickled red blood cells

Sickle-Cell Anemia • Detection/Treatment – Blood screening can detect disorder – In a fetus, disorder can be detected by amniocentesis