Transcript Human Genetics

Human Genetics
Human Chromosomes
• 23 Pairs
•
•
- 22 Autosomes
- 1 Sex chromosome
1 set contributed by
mother
1 set contributed by
father
Chromosomal disorders
• How many chromosomes does a normal
human gamete have?
• What happens if a gamete fails to
separate chromosomes properly?
- Nondisjunction – results in….
- Aneuploidy – any difference from the
normal 46 chromosomes
When does nondisjunction happen?
How do you diagnose
nondisjunction? Karyotyping
• Picture of the
•
chromosomes
Sample collected by
Amniocentesis in at
risk mothers
- mothers over 35
- families with
histories of genetic
disorders
Normal Karyotypes
46, XX
46, XY
Nondisjunction disorders
• Down Syndrome
•
- Extra copy of the 21st Chromosome
- 47, X_, +21
- 1/700 live births in the US
Characteristics
- characteristic facial features, short stature; heart
defects
- susceptibility to respiratory disease, shorter lifespan
- prone to developing early Alzheimer's and leukemia
- often sexually underdeveloped and sterile, usually
some degree of mental retardation.
- Down Syndrome is correlated with age of mother but
can also be the result of nondisjunction of the father's
chromosome 21.
Nondisjuncton in sex chromosomes
• Turner’s Syndrome (Monosomy X)
•
- 45, X
- 1/5000 live births
Characteristics
- short stature
- characteristic “webbed” neck
- infertile
- normal mental development
• Klinefelter’s Syndrome
- 47, XXY
• Characteristics
- Male sex characteristics
- Underdeveloped testes
- Sterile
- Some female secondary sex
characteristics (breast and hip growth)
Can you tell what is going on in this
karyotype?
Can you tell what is going on in this
karyotype?
Patau Syndrome
• Trisomy 13
- Severe mental and physical problems
- Cleft lip, palate, small head, heart
problems, small limbs
What is wrong here and what
would be the notation?
Edwards Syndrome
• Trisomy 18
- Severe mental and physical disabilities
- Rarely live past one year
What is wrong here?
Other Chromosomal Disorders
• Translocations : Philadelphia Translocation
t(9;22)(q34;q11.2)
• Deletions : Fragile X, Cri du Chat
• Duplications : Rare
Cri du Chat Syndrome
• High pitch cry (cat
•
•
•
•
like)
Downward eye slant
Mental retardation
Partially webbed
fingers or toes
Small head and eyes
Following Traits : Pedigrees
• Chart showing relationships and tracing a
particular trait through a family
Autosomal Dominant
• Appears in every generation
• An afflicted child must have an afflicted
parent
Example: Huntington’s Disease
• Autosomal dominant CAG
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•
•
•
repeat
Degeneration of nerves
Person begins life
normally
Nerves degenerate over
time
Jerky motion, slurred
speech, mental
retardation
Other Dominant Diseases
• Achondroplasia – Dwarfism
• Hypercholesterolemia – high cholesterol
• Osteogenesis imperfecta – brittle bones
• Polydactyly – 6 fingers and toes
• Many others
Recessive Disorders
• Appears intermittently through
generations (up to 25% of individuals)
• No sex preference
• Afflicted child does not necessarily have
an afflicted parent
Example : Albinism
• Lack of pigment in
•
•
skin, hair and eyes
No common negative
health problems
besides increased risk
of skin cancer
Defective gene for the
production of melanin
Example: Cystic Fibrosis
• Thick, sticky
mucous
• Effects all secretory
organs
• CFTR protein has a
single AA change
Other Recessive Disorders
• Phenylketonuria – accumulation of
phenylalanine in tissues
• Tay-Sachs disease – lipid accumulation in
brain cells
• Galactosemia – inability to metabolize
galactose
• Many others
Codominant disorder: Sickle cell
anemia
• NN = normal
•
hemoglobin
Nn = sickle cell trait
nn = sickle cell
anemia
Evolution: Library: A
Mutation Story
Sex-Linked Inheritance
• Trait only (usually)
•
expressed in males
Skips generations in
families
Hemophilia in the Royal Family
Other sex-linked recessive
disorders
• Duchene muscular dystrophy
• Red-green colorblindness
• Fragile-X syndrome
Imprinting and Disorders
Prader Willi Syndrome
Angelman Syndrome
Blue people of Troublesome Creek