KARYOTYPE AND GENETIC DISORDERS

H. Biology

Chromosomes Determine Your Gender

• Humans have 23 pairs of chromosomes• 22 pairs are autosomes (chromosomes

that are NOT involved in making gender)• Also called homologous chromosome pairs

• 1 pair are sex chromosomes (NOT HOMOLOGOUS; different genes)• The sex chromosomes are “X” and “Y”

• “XX” is a girl• “XY” is a boy

XY

Y

X

Egg cells ALWAYS have “X”

chromosome

5 µmPair of homologouschromosomes

Centromere

Sisterchromatids

A karyotype

• an ordered, visual representation of ALL chromosomes in a human cell

• Arranged according to homologous pairs

a REAL

view…wow!!

!

What is a genetic disorder? What causes a genetic disorder?

• Caused by an abnormality in an individual’s DNA

How do these abnormalities occur?

1) Non-disjunction • Addition or subtraction of chromosome or set of

chromosomes

2) Mutations • Change to DNA sequence (gene)

Abnormal Chromosome Number

• When nondisjunction occurs• Pairs of homologous chromosomes do NOT separate

normally during meiosis • Gametes contain 2 copies or NO copies of a particular

chromosome

• What are some disorders caused by non-disjunction?

• Downs Syndrome• Trisomy 21

• Klinefelter’s Syndrome• XXY

• Turner Syndrome• Monosomy X

What happens when meiosis goes wrong?

NONDISJUNCTION!!!

Meiosis I

Nondisjunction

Meiosis II

Nondisjunction

Gametes

n + 1n + 1 n 1 n – 1 n + 1 n –1 n n

Number of chromosomes

Nondisjunction of homologouschromosomes in meiosis I

Nondisjunction of sisterchromatids in meiosis II

(a) (b)

AneuploidyResults from the fertilization of gametes in which nondisjunction occurred

Offspring have an abnormal number of a particular chromosome

What are some disorders caused by non-disjunction?• Downs Syndrome

• Trisomy 21

• Kleinfelter’s Syndrome• XXY

• Edwards Syndrome• Trisomy 18

• Patau Syndrome• Trisomy 13

• Turner Syndrome• Monosomy X

1.) Trisomy 18-Edwards Syndrome

2.) Trisomy-13: Usually Fatal

3.) Klinefelter - XXY

• Klinefelter syndrome• a result of an extra

chromosome in a male, producing XXY individuals

• 1/2000 live births

XYY individuals

Triple X Syndrome XXX individuals

•Females

•Healthy

•Same phenotype as XX individuals

•1/1000 live births

4.) Turner Syndrome

• Turner syndrome• Is the result of

monosomy X, producing an X0 karyotype

• 1/5000 live births• Only known

monosomy in humans

• Normal intelligence• Sterile

5.) Trisomy 21

Human Disorders Due to Chromosomal

Alterations

• Down syndrome• Is usually the

result of an extra chromosome 21• trisomy 21

What are some disorders caused by mutations?

• Sickle cell anemia (recessive)

• Cystic fibrosis (recessive)

• Maple syrup urine disorder (recessive)

• Congenital hypothyroidism (recessive)

• Huntington’s Disease (dominant)

Cystic Fibrosis

• Example of recessive disorder

• Affect mostly people of European descent

• Symptoms • Mucus buildup in the some

internal organs• Abnormal absorption of

nutrients in the small intestine

Sickle Cell AnemiaoAnother recessive disorderoAffects one out of 400 African-AmericansoHemoglobin is the O2 carrying protein in red blood cells o SCA is an inherited blood disease where hemoglobin clumps together

causes red blood cells to stiffen and curl into a sickle/crescent shapeo Because of this, the RBC cannot transport O2 effectively

SymptomsPhysical weakness, pain, organ damage, and even paralysis

24

Human Chromosomal Disorders

Recessive Disorders

• Cystic Fibrosis • Excess mucus in lungs, digestive tract, liver• More susceptible to pneumonia, infection• Early death ~ average age of 37

• Tay-Sachs• Lipid accumulation in brain cells, mental retardation• Blindness, death in childhood

Dominant Disorder

• Huntington’s disease • Deterioration of nervous system, uncontrollable

movements• Develops in middle age, death soon after

Dominantly Inherited Disorders

• Some human disorders• Are due to dominant

alleles only need 1 dominant allele

• Example is achondroplasia• Form of dwarfism lethal

when homozygous for the dominant allele

Another Dominant Disorder

• Huntington’s disease (HD)• degenerative disease of nervous

system• No obvious phenotypic effects until

about 35 to 40 years of age

HD

Normal