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

XYY

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 effectivelySymptoms

Physical weakness, pain, organ damage, and even paralysis

24

Human Chromosomal DisordersRecessive 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