the sequences of bases in dna are like the letters of a coded message… what would happen if a few...

The sequences of bases in DNA are like the letters of a coded message… what would happen if a few of those letters changed accidentally, altering the message??

Could the cell still understand its meaning?

Mutation: a mistake or variation in the bases of DNA- mutations are heritable changes in genetic information.

Spontaneous Change in Hereditary Material caused by replication errors or environmental factors

Genes or chromosomes

Some harmful; Some notDNA replicates during the S phase of interphase (prior to mitosis). If an error occurs during this process, DNA polymerase usually fixes the mistake. A mutation is the FAILURE of the DNA repair system to fix the error.

Point mutations: gene mutations that involve changes in one or a few nucleotides

Substitution: 1 base is changed to a different base in the DNA sequence

*think substitute teacher (switch)Frameshift (Insertion or Deletion): 1

base is inserted or removed from the DNA sequence

*think adding another teacher to the room or removing the teacher completely (not going to happen! )

1) Single Point Mutations- 1 base gets replaced w/ another • Ex: ACCTG AACTG• Can lead to change in the

codon change in amino acid change in protein change in trait

• EX: change in protein can cause normal red blood cells to have crescent (sickle shape)

Fig. 17-22

Wild-type hemoglobin DNA

mRNA

Mutant hemoglobin DNA

mRNA

33

3

3

3

3

55

5

55

5

C CT T TTG GA A AA

A A AGG U

Normal hemoglobin Sickle-cell hemoglobin

Glu Val

Silent mutations have no effect on the amino acid produced by a codon because of redundancy in the genetic code

Missense mutations still code for an amino acid, but not necessarily the right amino acid

Nonsense mutations change an amino acid codon into a stop codon, nearly always leading to a nonfunctional protein

Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings

Fig. 17-23a

Wild type

3DNA templatestrand

3

355

5mRNA

Protein

Amino endStop

Carboxyl end

A instead of G

33

3

U instead of C

55

5

Stop

Silent (no effect on amino acid sequence)

Fig. 17-23b

Wild type

DNA templatestrand

35

mRNA

Protein

5

Amino endStop

Carboxyl end

53

3

T instead of C

A instead of G

33

3

5

5

5

Stop

Missense

Fig. 17-23cWild type

DNA templatestrand

35

mRNA

Protein

5

Amino endStop

Carboxyl end

53

3

A instead of T

U instead of A

33

3

5

5

5

Stop

Nonsense

2)

Frame Shift- when a base is either deleted or added. This means the READING FRAME is changed and the bases “downstream” will be regrouped = disastrous results.

EX: Deletion CCAGT CCGT Insertion CCAGT CCAAGTAgain, can lead to a change in codon…

trait!!!

Huntington’s Disease - The triplet CAG is repeated. This adds a string of glutamines to the protein called huntington. This abnormal protein increases the level of p53 protein in brain cells causes their death by apoptosis. This degeneration causes uncontrolled movements, loss of intellectual faculties and emotional disturbance.

Muscular Dystrophy - CTC and CCTG repeats. This disease is characterized by the progressive weakness and degeneration of the skeletal muscles.

Insertion of 2 nucleotides (A & T) - 2566Deletion of one C - 3659Deletion of 3 nucleotides at 1654-1656Generally results in abnormal amounts of

salt which leads to a thick sticky mucus coating which coats cells - particularly the lungs.

Harmful Effects: Those that dramatically change protein structure or gene activity.*Example: Some cancers are the product of mutations that cause uncontrolled cell growth of cells.

Beneficial Effects: Those that produce proteins with new or altered functions that may be useful to organisms in different/changing environments. *Example mutations have allowed for insects to resist chemical pesticides. Good for insects, bad for farmers & our food!

Mutagens are external agents that cause mutations.

EX:Radiation from x-rays, UV

lightViruses - human papilloma

virusEnvironmental poisons-

tobacc0Carcinogens-cancer

causing chemical(s)

Cancer causing chemical(s)

Cancer causing genes that can affect the division and differentiation of a cell. These may be turned “on” by the presence of a carcinogen and lead to cancer

•Spontaneous change involving an entire chromosome or pieces of a chromosome

•More to come during Meiosis…..

Can occur during meiosis

Some harmful, some not

Bigger effect than gene mutations

2 types: Structural mutations and Numerical Mutations

Deletion- one or more genes are lost

Duplication- extra piece duplicated genes

Translocation- piece of a chromosome breaks off of one & attaches to another different chromosome

Inversion- piece of a chromosome breaks off and reattaches itself backwards

Usually results from nondisjunction- failure of chromosomes to separate

Monosomy- zygote receives only 1 of a particular chromosome

EX: female being XO or getting 1 # 6 chromosome

Trisomy- zygote receives 3 chromosomes of a particular kind

Down’s Syndrome - extra 21st chromosome

XXY - 47 Males

Polyploidy- none of the chromosomes separate and the zygote gets 3 or more sets of chromosomes

EX: instead of 23 pairs, you get 46 pairs of chromosomes…this means 92 chromosomes!!!