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Mutations  Mutations are defined as “a sudden genetic change in the DNA sequence that affects genetic information”.  They can occur at the molecular.

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Presentation on theme: "Mutations  Mutations are defined as “a sudden genetic change in the DNA sequence that affects genetic information”.  They can occur at the molecular."— Presentation transcript:

1 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.

2  Things that can cause mutations are called “mutagens”.  Known mutagens are ultraviolet light, cigarette smoking, certain chemicals like PCB’s.

3 Effects of Mutations  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

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 (cancer)

5 Types of Mutations – mistakes a)Gene (point) Mutations – effects a single gene i. Substitution ii. Frameshift a)Chromosomal mutations – most drastic, change in structure or # of chromosomes (affects many genes)

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

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

8 a)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

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10  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

11 Aneuploidy Polyploidy

12 Down’s Syndrome Trisomy 21 1 in 700 births Mental retardation Males are sterile but females are not

13 Likelihood of chromosomal mutations  1 in 1700 for mothers < 20.  1 in 1400 for mothers >20<30.  1 in 750 for mothers >30<35.  1 in 16 for mothers >45.

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

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16 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

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

18 Other Chromosomal Mutations  Affect many different genes  Caused by errors in meiosis or environmental disturbances

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20  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

21  Deletion – occurs when a piece of a chromosome breaks off and is lost  Duplication – occurs when a segment of a chromosome is repeated

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


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