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

MutationsMutations 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.

Things that can cause mutations are called “mutagens”.

Known mutagens are ultraviolet light, cigarette smoking, certain chemicals like PCB’s.

Effects of MutationsSilent mutations - have no effect on the expression of the gene. Causes for this type of mutation:

It is in a non-coding regionIt does not change the amino acid sequenceThe change does not affect the folding of the protein

Inheritability of MutationsIt depends on where it occurs

i.Germ mutations – occur in gametes. Inheritable (colorblindness, hemophilia)

ii.Somatic mutations – affect body cell, not inheritable (cancer)

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)

III. Point Mutations

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

Effects of substitution mutations

Missense mutations – causes a change in the amino acid coded for

Nonsense mutations – causes a stop codon to occur prematurely

a) Frameshift – affects several amino acids

-Insertion – 1 base is inserted, affects several amino acidsEx. (GCA-TCA GCA-GTC-

A

-Deletion – base is removed, affects several amino acids

Ex. (GCA-TCA GCT-CA

Chromosome mutationsNondisjunction – 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

AneuploidyPolyploidy

Down’s Syndrome•Trisomy 21

•1 in 700 births

•Mental retardation

•Males are sterile but females are not

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.

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

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

Turner’s Syndrome•XO genotype—Monosomy X

•1 in 2,500 births

•Short, sterile

•75% result in non-disjunction from the father

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

disturbances

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

Deletion – occurs when a piece of a chromosome breaks off and is lostDuplication – occurs when a segment of a chromosome is repeated

XYY-Jacob’s Syndrome a.k.a. “Super Males”

• 1 in 1,000 men

•Normal appearance, very tall

•Low IQ, prone to violence