Understanding Genetic Disorders and Screening Methods

1. Genetic Disorders AP Biology

2. Detecting Genetic Disorders • Amniocentesis • Chorionic villus sampling • Karyotype • Sequential Screen (Quad/Triple Screen) • Blood Test

3. AmniocentesisA 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.

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

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

7. Karyotype

8. Normal Male

9. Normal Female

10. 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 2n+1 • 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

11. Nondisjunction Disorders • Down’s Syndrome - Trisomy 21 • Edward’s Syndrome - Trisomy 18 • Patau’s Syndrome - Trisomy 13 • Turner’s Syndrome - X0 • Klinefelter’s Syndrome - XXY • Super Male - XYY • Super Female - XXX

12. Down’s Syndrome Characteristic facial features, low mental ability, stocky build, sometimes heart defects. Extra copy of chromosome #21 –Trisomy 21

13. Edward’s Syndrome • Trisomy 18 • Motor and mental retardation • Congenital heart disease • Often dies in infancy

14. Patau’s Syndrome • Trisomy 13 • Physical abnormalities – cleft palate, polydactaly, microcephaly

15. 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

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

17. Super Male • XYY Jacob’s Syndrome • Male with extra Y chromosome • Very tall, can show violent behavior • Prone to acne • Impaired fertility • Mentally normal

18. Chromosomal Abnormalities

20. Short Arm of # 5 • Cri – du- chat • Cat-like cry • Severe physical and mental abnormalities • nonlethal

21. 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 mutationalters the ‘reading frame’ of triplets • THE FAT CAT ATE … • THF ATC ATA TE….

22. 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 unactivate relocated gene – which may produce a point mutation and could result in the elimination of a vital metabolic pathway

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

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

26. Autosomal Dominant • Huntington’s Disease • Marfan Syndrome • Achondroplasia

27. Huntington’s Disease Autosomal Dominant Disorder (lethal) • CNS problem • Dementia • Impaired memory • Asymptomatic until later in life (40)

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

29. 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

30. Autosomal Recessive • PKU • Albinism • Tay Sachs • Cystic Fibrosis

31. 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

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

33. 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

34. 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

35. 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

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

37. 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

38. Colorblindness