1. MUTATIONS How mistakes are made…

2. Mutations  Mutations are defined as “a sudden genetic change in the DNA sequence that affects genetic information”.  They can occur at the molecular level (genes) and change a single gene, or at the chromosome level and affect many genes.

3.  Things that can cause mutations are called “mutagens”.  Known mutagens are ultraviolet light, cigarette smoking, some viruses, certain chemicals like PCB’s.  Mutagens often result in cancer.

4. Inheritability of Mutations It depends on where it occurs i.Germ mutations – occur in gametes. Inheritable (colorblindness, hemophilia) ii.Somatic mutations – affect body cell, not inheritable (CAN RESULT IN cancer)

5. Effects of Mutations Not all mutations have effects. Silent mutations - have no effect on the expression of the gene.  Causes for this type of mutation:  It is in a non-coding region  It does not change the amino acid sequence  The change does not affect the folding of the protein

6. Types of Mutations a)Point Mutations – effects a single gene i. Substitution ii. Frameshift a. deletion b. insertions b)Chromosomal Mutations – most drastic, change in structure or # of chromosomes (affects many genes)

7. III.Point Mutations a)Substitution – one base exchanges for another, affects 1 amino acid (Ex. GCA-TCA  GCT-TCA

8. The Effects of Point Mutations ► A point mutation is a change in a single base pair in DNA.  A change in a single nitrogenous base can change the entire structure of a protein because a change in a single amino acid can affect the shape of the protein. Normal Point mutation mRNA Protein Stop mRNA Protein Replace G with A

9. Effects of substitution mutations  Missense mutations – causes a change in the amino acid coded for  Nonsense mutations – causes a stop codon to occur prematurely

10. Sickle cell anemia

11. Tay-Sachs

12. Frameshift Mutations ► What would happen if a single base were lost from a DNA strand? ► A mutation in which a single base is added or deleted from DNA is called a frameshift mutation because it shifts the reading of codons by one base.  As a result, every codon after the deleted base would be different. mRNA Protein Deletion of U

13. Frameshift – affects several amino acids -Insertion – 1 base is inserted, affects several amino acids Ex. (GCA-TCA  GCA-GTC-A -Deletion – base is removed, affects several amino acids Ex. (GCA-TCA  GCT-CA

14. X

15. Cystic fibrosis

16.  Chromosome mutations  Nondisjunction – incomplete chromosome division during meiosis; results in gametes with too many or too few chromosomes.  Ex: Down syndrome is caused by an extra #21 chromosome

18. Aneuploidy Polyploidy

19. Down’s Syndrome Trisomy 21 1 in 700 births Mental retardation Vision problems Heart problems

20. Likelihood of chromosomal mutations  1 in 1700 for mothers under 20.  1 in 1400 for mothers between 20 and 30.  1 in 750 for mothers between 30 and 35.  1 in 16 for mothers over 45.

21.  Sex chromosome disorders – occurs as a result of nondisjunction of the sex chromosomes  Ex: Turner’s syndrome – X-; Klinefelter’s syndrome – XXY.

23. Klinefelter’s Syndrome XXY 1 in 1,000 Usually sterile because of low sperm count Tall, sparse body hair Suffer from gynecomastia- male breast tissue Testosterone treatments

24. Turner’s Syndrome XO genotype—Monosomy X 1 in 2,500 births Short, sterile 75% result in non-disjunction from the father

25. XYY-Jacob’s Syndrome a.k.a. “Super Males” 1 in 1,000 men Normal appearance, very tall Low IQ, prone to violence

26. Patau’s Syndrome 1 out of 6,000 births Trisomy 13 80-90% do not survive past 1 yr old

27. Edward’s Syndrome Trisomy 18 Second most common trisomy after down’s syndrome Only 5% live to age 1 1 out of 8,000 births Severely retarded, many die from malformed heart Polydactyly or syndactyly

28. Other Chromosomal Mutations  Affect many different genes  Caused by errors in meiosis or environmental disturbances.

29.  Translocation – occurs when a piece of one chromosome breaks off and attaches to a nonhomologous chromosome  Inversion – occurs when a piece of one chromosome breaks off, flips, and reattaches to the same chromosome

30.  Deletion – occurs when a piece of a chromosome breaks off and is lost  Duplication – occurs when a segment of a chromosome is repeated

32. Cri du Chat “Cry of the Cat” 1 in 50,000 births A piece of chromosome 5 is missing Severe mental retardation, nonverbal Does not run in families