DNA Mutations & Disorders

Normal Protein Formation

1. A segment of DNA strand is copied by mRNA in the nucleus.

2. mRNA leaves nucleus and goes to ribosome in cytoplasm.

3. Ribosome “reads” mRNA and calls for specific amino acids.

4. Amino acids linked together to form protein chain.

Abnormal Protein Formation

• Mutations in DNA will code for wrong amino acids which will cause wrong protein to form.

• Can lead to cell death, disease, disorders

What is a mutation?

• Any change in a gene or chromosome.

• Most are natural and have no effect on the organism- can promote good genetic diversity

• Some are harmful• Some are lethal (cause death in

offspring)• Some are good for the organism

(ex: some mosquitoes have a gene mutation that makes them resistant to pesticide- leads to evolution of stronger mosquito populations)

What are some types of mutations?

1. Point mutation- change in ONE single nitrogen base in ONE gene.• This change causes

the code to change so amino acids are not put in correct order.

• EX: albinism, sickle cell anemia

Types of Point Mutations

A. Silent- one letter change but no change in amino acid= no change in protein structure= no problems

B. Missense- one letter change causes changed amino acid= wrong protein structure

C. Nonsense- one letter change causes STOP codon in middle of amino acid chain= protein won’t get made

(Normal)

What are some types of mutations?

2. Chromosome Mutations (Frameshift)- changes in MANY genes, entire segments of chromosome are messed up.

• Because more genes are involved, usually more harmful to the organism.

A. Deletion- part of chromosome is lost

B. Duplication- part of chromosome is repeated twice

C. Inversion- chromosome breaks, piece is turned over & reinserted upside down

D. Translocation- two chromosomes affected- one piece detaches & reattaches to another chromosome

A

B

C

D

E. Insertion- a nitrogen base is added which causes nitrogen bases to shift to the right, throws off amino acid sequence.

F. Nondisjunction- a chromosome pair fails to separate properly during meiosis (some sperm/egg get too many chromosomes, some get too few).– Monosomy- too few (45

chromosomes)– Trisomy- too many (47

chromosomes)

What are some causes of mutations?

1. Mutagen- anything that causes a mutation in DNA in a cell.– UV light– Radiation– X rays– chemicals in tobacco smoke, synthetic materials, pollution– viruses

What is the difference between germ cell mutation & somatic cell

mutation?

• Germ Cell mutation:– Occurs in gametes

(sperm/egg)– Does not affect

individual person– CAN be passed to

offspring

• Somatic Cell mutation– Occurs in body cells– Affects individual in

which it occurs– CANNOT be passed

to offspring– If occurs in genes that

control cell reproduction can become CANCER.

What are some methods of detection?

• Ultrasound- sound waves generate image of unborn child. Detect abnormalities of limbs, organs, etc.

What are some methods of detection?

• Amniocentesis: use needle to extract fluid/cells surrounding the fetus. Chromosomes can then be karyotyped

What are some methods of detection?

• Karyotyping: pictures of chromosomes are matched up according to size

Difference between Autosomes & Sex Chromosomes

1. Autosomes- first 22 pairs of chromosomes in karyotype

2. Sex Chromosomes- last pair of chromosomes that determine gender

3. Male karyotype- sex chromosomes are a big chromosome (X) and a small chromosome (y)

4. Female karyotype- sex chromosomes are two big chromosomes (XX)

What are some types of genetic disorders

1. Autosomal Dominant- if dominant gene is present, person will have disorder– Huntington’s disease– Achondroplasia

HUNTINGTON’S DISEASE

• Caused by dominant allele

• Develops after age 30

• Lose muscle control, mental deterioration, & eventually death.

• No cure

Achondroplasia

• Dwarfism• Defect in gene that

controls cartilage formation

• Shortened stature• Some have normal

sized torso but shortened limbs.

What are some types of genetic disorders?

2. Autosomal Recessive- must have two recessive genes to show disorder– Phenylketonuria– Cystic Fibrosis– Tay-Sachs– Sickle cell anemia

PHENYLKETONURIA

• Also called PKU• Must inherit two recessive alleles to show this

disease.• Unable to synthesize the enzyme that breaks

down the amino acid phenylalanine. Phenylalanine accumulates and kills brain cells.

• Tested at birth- if present, put on diet low in phenylalanine (no milk) for first six years to prevent brain damage.

CYSTIC FIBROSIS• Also called CF

• Caused by a recessive allele

on chromosome #7.

• Serious digestive problems, thick mucus that clogs lungs. Makes breathing & digesting food very difficult.

TAY-SACHS DISEASE

• Caused by two recessive alleles

• Occurs mostly in Jewish families

• Fats accumulate in brain cells, mental deficiency, delayed development, blindness

• Usually results in death within first few years of life.

SICKLE-CELL ANEMIA• Red blood cells are

half moon shaped instead of round.

• Clog blood vessels, depriving tissues of oxygen- causes severe pain, weakness.

• Found more often in people of African descent.

What are some types of genetic disorders?

3. Sex-Linked- disorder on sex chromosomes– Klinefelters

syndrome– Turner’s syndrome– XYY males

KLINEFELTERS SYNDROME

• Males with an extra X chromosome

• XXY

• Sterile

• Some degree of mental deficiency

TURNER’S SYNDROME

• Females with only one X chromosome.

• XO

• Sterile

• Short, with thick, webbed necks, mild mental deficiency.

XYY MALES

• Males with extra Y chromosome

• taller than average• Produce more

testosterone, some say more aggressive