KARYOTYPE AND GENETIC DISORDERS H. Biology. Chromosomes Determine Your Gender Humans have 23 pairs...
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Transcript of KARYOTYPE AND GENETIC DISORDERS H. Biology. Chromosomes Determine Your Gender Humans have 23 pairs...
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
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
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
• Klinefelter syndrome• a result of an extra
chromosome in a male, producing XXY individuals
• 1/2000 live births
Triple X Syndrome XXX individuals
•Females
•Healthy
•Same phenotype as XX individuals
•1/1000 live births
• Turner syndrome• Is the result of
monosomy X, producing an X0 karyotype
• 1/5000 live births• Only known
monosomy in humans
• Normal intelligence• Sterile
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