Genetic Disorders

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Genetic Disorders

• AP Biology

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Detecting Genetic Disorders

• Amniocentesis
• Chorionic villus sampling
• Karyotype
• Sequential Screen (Quad/Triple Screen)
• Blood Test

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• Amniocentesis A technique for determining genetic
  abnormalities in a fetus by the presence of
  certain chemicals or defective fetal cells in the
  amniotic fluid, obtained by aspiration from a
  needle inserted into the uterus.

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CVS sample of embryonic cells taken for
chorionic villus (placenta) can be done earlier
than amniocentesis and results yielded sooner
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Karyotype

• A method of organizing the chromosomes of a cell
  in relation to number, size, and type. Taken
  during METAPHASE of Mitosis.

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Karyotype
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Normal Male
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Normal Female
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NON-DISJUNCTION

• Chromosomes fail to separate properly - can occur
  during meiosis I (all cells affected) or meiosis
  II (half cells affected)
• Aneuploidy - having an abnormal chromosome number
• Trisomic/TRISOMY - having 3 chromosomes 2n1
• Monosomic - having 1 chromosome 2n-1
• Polyploidy - having move than 2 sets of
  chromosomes
• Triploidy - (3n)
• Tetraploidy - (4n) common in plants usually
  lethal in animals and humans

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Nondisjunction Disorders

• Downs Syndrome - Trisomy 21
• Edwards Syndrome - Trisomy 18
• Pataus Syndrome - Trisomy 13
• Turners Syndrome - X0
• Klinefelters Syndrome - XXY
• Super Male - XYY
• Super Female - XXX

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Downs Syndrome
Characteristic facial features, low mental
ability, stocky build, sometimes heart defects.
Extra copy of chromosome 21 Trisomy 21
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Edwards Syndrome

• Trisomy 18
• Motor and mental retardation
• Congenital heart disease
• Often dies in infancy

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Pataus Syndrome

• Trisomy 13
• Physical abnormalities cleft palate,
  polydactaly, microcephaly

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Turner Syndrome

• XO
• Female missing one X chromosome
• short stature
• wide neck with extra skin folds
• underdevelopment of sex characteristics may
  lead to sterility
• non-disjunction of sex chromosomes

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Klinefelters Syndrome XXY

• XXY
• male with extra X chromosome
• poor sexual development, may be sterile
• subnormal mental ability
• other forms are XXYY, XXXY, XXXXY (additional
  Xs increase the severity of phenotypes and
  mental retardation)

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Super Male

• XYY Jacobs Syndrome
• Male with extra Y chromosome
• Very tall, can show violent behavior
• Prone to acne
• Impaired fertility
• Mentally normal

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Chromosomal Abnormalities
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Short Arm of 5

• Cri du- chat
• Cat-like cry
• Severe physical and mental abnormalities
• nonlethal

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Gene Mutations

• Point mutations
• Changes in 1 or a few base pairs in a single gene
• Substitutions
• Base-pair insertions or deletions - Can result
  in a frameshift mutation alters the reading
  frame of triplets
• THE FAT CAT ATE
• THF ATC ATA TE.

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Gene Abnormalities

• Point
• Substitution
• Silent no change in aa
• Nonsense STOP CODON
• Missense change in aa
• THE FAT CAT ATE THE RAT ? TOE FAT CAT ATE THE
  RAT
• Insertion/Addition
• Deletion
• May result in a Frame-Shift Mutation
• THE FAT CAT ATE THE RAT ? THF ATC ATA TET HER AT
• (ENTIRE MESSAGE SHIFTS)
• Transposons (jumping genes) transfer of a gene
  from one locus to another on a chromosome may
  unactivated relocated gene which may produce a
  point mutation and could result in the
  elimination of a vital metabolic pathway

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Sickle Cell Anemia

• Abnormal hemoglobin
• 1 aa substitution causes abnormality (point
  mutation)
• Codominance (carrier)
• Low oxygen RBC will become crescent shape

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Inherited Genetic Disorders

• Autosomal Dominant
• Inherit one allele
• Autosomal Recessive
• Must inherit two recessive alleles, one from each
  parent. Parents are usually CARRIERS of the
  disorder
• Sex-Linked Disorders
• Usually recessive, inherited on X-chromosome
• More common in males

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Autosomal Dominant

• Huntingtons Disease
• Marfan Syndrome
• Achondroplasia

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Huntingtons Disease Autosomal Dominant Disorder
(lethal)

• CNS problem
• Dementia
• Impaired memory
• Asymptomatic until
• later in life (40)

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Marfan Syndrome

• Autosomal Dominant
• Connective tissue defect
• Tall, thin, long arms and legs
• Enlarged aorta
• Abe Lincoln did NOT have
• Marfan Syndrome

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Achondroplasia

• Autosomal Dominant
• Defects in growth of long bones
• Form of dwarfism
• Short arms and legs but torso of normal size,
  large head compared to body

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Autosomal Recessive

• PKU
• Albinism
• Tay Sachs
• Cystic Fibrosis

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PKU

• Phenylketonuria
• Autosomal Recessive
• Lack enzyme to convert phenylalanine to tyrosine
• Buildup of phenylalanine can cause retardation
• Test babies at birth
• Special diet for phenylketonurics

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Albinism

• Lack of pigmentation in skin, hair, eyes
• Inability to make melanin
• Autosomal recessive

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Tay-Sachs

• Autosomal recessive
• Degeneration of nervous system
• No enzyme to break down lipids in brain cells, so
  they swell and die (death by age 5) - Lethal
• High incidence in Ashkenazie Jews
• Blood test available to potential parents

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Cystic Fibrosis

• Cystic Fibrosis, incurable hereditary disorder
  that causes the body to secrete an abnormally
  thick, sticky mucus that clogs the pancreas and
  the lungs, leading to problems with breathing and
  digestion, infection, and ultimately, death.
• Common among Caucasians
• One of the most common fatal genetic disorders in
  the United States
• Lethal
• Autosomal recessive, caused by missing 3 bases/1
  aa (phenylalanine) protein does not fold correctly

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Sex-Linked Traits

• Gene loci on a sex-linked chromosome
• Genes for many sex-linked traits, unrelated to
  gender, are found on the X chromosome
• Follow Mendelian Laws of Inheritance
• May be either dominant or recessive
• Hemophilia
• Duchenne Muscular Dystrophy
• Colorblindness

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Hemophilia

• Sex-linked recessive disorder
• Lack of protein necessary for normal blood
  clotting

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Duchenne Muscular Dystrophy

• Sex-linked recessive disorder
• Absence of muscle protein dystrophin
• Progressive muscle deterioration and loss of
  coordination most die by age of 20

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Colorblindness