human genetics
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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? - PowerPoint PPT PresentationTRANSCRIPT
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Human Genetics
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Human Chromosomes• 23 Pairs - 22 Autosomes - 1 Sex
chromosome• 1 set contributed
by mother• 1 set contributed
by father
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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
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When does nondisjunction happen?
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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
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Normal Karyotypes
46, XX 46, XY
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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.
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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
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• Klinefelter’s Syndrome - 47, XXY• Characteristics - Male sex characteristics - Underdeveloped testes - Sterile - Some female secondary sex
characteristics (breast and hip growth)
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Can you tell what is going on in this karyotype?
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Can you tell what is going on in this karyotype?
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Patau Syndrome• Trisomy 13 - Severe mental and physical
problems - Cleft lip, palate, small head, heart
problems, small limbs
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What is wrong here and what would be the notation?
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Edwards Syndrome• Trisomy 18 - Severe mental and physical
disabilities - Rarely live past one year
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What is wrong here?
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Other Chromosomal Disorders• Translocations : Philadelphia
Translocation t(9;22)(q34;q11.2)
• Deletions : Fragile X, Cri du Chat
• Duplications : Rare
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Cri du Chat Syndrome• High pitch cry (cat
like)• Downward eye
slant• Mental retardation• Partially webbed
fingers or toes• Small head and
eyes
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Following Traits : Pedigrees• Chart showing relationships and
tracing a particular trait through a family
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Autosomal Dominant• Appears in every generation• An afflicted child must have an
afflicted parent
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Example: Huntington’s Disease• Autosomal dominant
CAG repeat• Degeneration of
nerves• Person begins life
normally• Nerves degenerate
over time• Jerky motion, slurred
speech, mental retardation
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Other Dominant Diseases• Achondroplasia – Dwarfism• Hypercholesterolemia – high
cholesterol• Osteogenesis imperfecta – brittle
bones• Polydactyly – 6 fingers and toes• Many others
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Recessive Disorders• Appears intermittently through
generations (up to 25% of individuals)
• No sex preference• Afflicted child does not necessarily
have an afflicted parent
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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
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Example: Cystic Fibrosis
• Thick, sticky mucous
• Effects all secretory organs
• CFTR protein has a single AA change
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Other Recessive Disorders• Phenylketonuria – accumulation of
phenylalanine in tissues• Tay-Sachs disease – lipid
accumulation in brain cells• Galactosemia – inability to
metabolize galactose• Many others
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Codominant disorder: Sickle cell anemia• NN = normal
hemoglobin Nn = sickle cell
trait nn = sickle cell
anemia• Evolution: Library:
A Mutation Story
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Sex-Linked Inheritance• Trait only (usually)
expressed in males• Skips generations
in families
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Hemophilia in the Royal Family
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Other sex-linked recessive disorders• Duchene muscular dystrophy• Red-green colorblindness• Fragile-X syndrome
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Imprinting and DisordersPrader Willi Syndrome Angelman Syndrome
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Blue people of Troublesome Creek