Mutations & Genetic Disorders

IN 141

Headings

Vocabulary

Important Information

MutationsMutationsMutation: Any mistake or change in the DNA sequence

Point mutation: Change in

one nitrogen base in DNA

Ex: albinism

Changes in chromosome structure

1) INVERSION: the order of genes on a

chromosome is inverted

Chromosomal Mutation:Chromosomal Mutation:

2) TRANSLOCATION:

•the movement of a chromosome fragment to a nonhomologus chromosome

3. DELETION Loss of a few bases Loss of large regions

of a chromosome

4. DUPLICATION Duplication of a few

bases Duplication of large

regions of a chromosome

Crossing OverCrossing Over

Occurs when chromosomes exchange genes.

2 chromosomes overlap.

Some genes cross over and switch places

NONDISJUNCTIONNONDISJUNCTIONNondisjunction: chromosome pair fails

to separate properly during meiosis

Monosomy: gamete has 1 less

chromosome than it should

45 chromosomes is the result

Ex: Turner syndrome Missing a sex

chromosome

Trisomy: Gamete has 1

more chromosome than it should

Result is 47 chromosomes

Ex: Down’s SyndromeExtra #21

chromosome

Methods of DetectionMethods of Detection

Ultrasound: Sound waves are used to

generate an image of the unborn child.

Used to detect abnormalities of limbs, organs, etc.

Chorion villi sampling: •Take sample of the chorion

–(membrane surrounding fetus)

•Chemical tests and KaryotypingKaryotyping performed

Amniocentesis: • Fluid surrounding the fetus is drawn out by

needle

• Fetal cells are collected and grown in a lab.

• Chromosomes can be then Karyotyped

Autosomal DisordersDown’s Syndrome (Trisomy 21)

Patau’s Syndrome (Trisomy 13)

Edward’s Syndrome (Trisomy 18)

Down’s Syndrome (DS) Excess # 21 chromosome Prenatal testing can be done Result of chromosomal mutation 1 in 900 people born with this Likelihood of having a child with DS

increases with advancing maternal age Symptoms: mental retardation, upward

slant to eyes, small mouth, abnormal ear shape, decreased muscle tone

No cure

Patau’s Syndrome &Edward’s Syndrome

Cardiac abnormalitiesVery severe conditionsMost affected infants

die during first few weeks of life

Deletion DisordersAngelman Syndrome

Prader-Willi Syndrome

Angelman SyndromeInappropriate

laughter with convulsions

Poor coordination

Mental retardation

Prader-Willi Syndrome

Extremely floppy Obesity (constantly

hungry)Mild mental

retardation

Sex Chromosome DisordersKlinefelter’s Syndrome

Turner’s Syndrome

Fragile X Syndrome

Klinefelter’s Syndrome 47, XXY 1 in 1000 male live births Mild learning difficulties Taller than average with

long lower limbs Show mild enlargement of

breasts Infertile (absence of

sperm) Treat with testosterone

Turner’s Syndrome

45, XLow incidenceLook normalOvarian failureNormal intelligenceShort statureEstrogen therapy

Fragile X Syndrome

Most common inherited cause of mental retardation

1 in 2000 malesHigh forehead,

prominent jaw, autismGap in X chromosome

Single Gene DisordersCystic Fibrosis

Hemophilia

Sickle Cell Anemia

Phenylketonuria

Cystic Fibrosis (CF) Recessive disorder Mutation stops production of

protein in lung cells, pancreas

Thick mucus, bacterial infections in lung

“sweat test” Most common in

Caucasians (1 in 3300) Chest percussions, diet

supplements Shortened life expectancy

Hemophilia

Sex-linkedFailure of blood to clotRare in females Injections with clotting factors to stop

bleeding episodes$350,000 a year in treatment

Sickle Cell Anemia Mutation in blood protein “sickle” shape to RBC Screening tests Most common in African-Americans

(1 in 375) Pain associated with blocked vessels, causes

anemia (fatigue) Common where

mosquito-borne malaria is present

PKU Mutation disrupts function of enzyme Leads to high phenylalanine levels in brain

(poisons) Mental retardation, epilepsy Screening newborns (heel prick) 1 in 10,000 Caucasian births Extremely rare in African-Americans Look normal Need low-protein diet,

smelly formulas

Self Quiz: Quick Check for Understanding

1. Which of the following is an X-linked disorder? A. Angelman B. hemophilia c. Down syndrome

2. How is PKU tested for? A. amniocentesis b. heel prick c. X-ray

3. How are CF patients treated? A. testosterone injections b. chest percussions

4. Turner’s Syndrome is A. 45, X b. 46, XX c. 47, XXY

5. Patients with Klinefelter’s Syndrome are A. all male b. all female c. male or female