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1976 1983 1988
GENETICS QUESTION - 1976 L. PETERSON/ECHS Each year a number of children are born with biological defects that impair normal function, For THREE of the following conditions, discuss such aspects as the biological cause, the methods of treatment and possible means of detection and/or prevention. a. Phenylketonuria (PKU) b. Sickle cell anemia c. Down syndrome d. Cretinism e. Erythroblastosis fetalis f. Blue-baby condition g. Tay-Sachs STANDARDS: maximum of 5 points for each section discussed = 15 PHENYLKETONURIA (PKU) Descriptive: mental retardation (1) light-colored hair, etc. (1/2) Cause: recessive (1/2) mutation (1/2) defect in amino acid metabolism (1) phenylalanine not converted to tyrosine (1/2) necessary enzyme lacking or ineffective (1/2) high phenylalanine or derivatives in mother's blood affects fetus (1/2) phenylalanine or derivatives excreted at high level (1) Treatment: phenylalanine in diet restricted during childhood (1) Detection: newborn's urine or blood tested (1/2) Prevention for phenylalanine or derivatives (1/2) heterozygotes in adults detected by phenylalanine tolerance test (1) SICKLE CELL ANEMIA Descriptive: common among sub-Sahara black populations & descendents (1/2) heterozygotes resistant to malarial infections (1/2) severe anemia (1/2) intense pain (1/2) shortened lifespan (1/2) Cause: recessive (1/2) mutation (1/2) behaves as semidominant in heterozygotes (1/2) substituted amino acid (1) in beta chain of hemoglobin (1) valine for glutamic acid at position 6 (1) red blood cells have low efficiency in O2 transport (1) red blood cells sickle, tend to clog smaller vessels (1) red blood cells have shortened lifespan, resulting in anemia (1) Treatment: transfusion of whole blood or packed cells (1) treatment of pain by drugs (1) Detection: red blood cells examined under microscope for sickling (1) heterozygotes detected by simple blood test (1) DOWN SYNDROME Descriptive: mental retardation (1) distinctive eyes (1/2) abnormal dermatoglyphics (1/2) thick tongue (1/2) shortened lifespan (1/2) low resistance to infection (1/2) possible derangement of internal organs (1/2) Cause: trisomy 21 (1) extra chromosome (1/2) nondisjunction as explanation of trisomy (1/2) 15/21 or other translocation (1/2) incidence of trisomy increases with age of mother (1) Treatment: no known cure (1) custodial care (1/2) special training (1/2) surgery to correct internal derangements (1/2) antibiotics to combat infections (1/2) Detection: amniocentesis (1/2) Prevention karyotype examination (1/2) possible decision to abort if trisomy present (1/2) pedigree & karyotype studies in young mothers of Down syndrome children for translocation involvement (1/2) counseling of older women about risks (1/2) CRETINISM Descriptive: mental retardation (1) growth retardation (1/2) low metabolic rate (1/2) yellow thick skin (1/2) distinctive eye structure (1/2) Cause: mainly developmental (non-genetic) (1) hypothyroidism (emphasis on gland) (1) hypothyroidism (lack of sufficient thyroxin) (1) low iodine in diet (1) low TSH production by pituitary (1) Treatment: thyroxin supplement (1) Detection: metabolic rate measured (1) Prevention protein-bound iodine test (PBI) (1) presence of thyroxin in blood tested (1/2) adequate iodine in diet assured (1/2) ERYTHROBLASTOSIS FETALIS Descriptive: lysis of red blood cells resulting in anemia (1/2) jaundice (1/2) physical malformation or edema (1/2) Cause: depends on recessive homozygous genotype in mother (1) mutation (1/2) description of induction of antibodies in Rh- mother as a result of carrying Rh+ fetus or previous transfusion (1) description of interaction of maternal antibodies w/red blood cells of (usually) second or later fetus (1) Treatment: replacement of newborn's blood supply (transfusion) (1) induction of early birth (1) Detection: Rh+ antibody formation suppressed in mother after birth of Rh+ fetus Prevention with Rhogam (gamma-globulin) (1) Rh+ antigen on red blood cells of parents tested (1) Rh+ antibody level monitored during pregnancy of mother (1) genetic counseling (1/2) BLUE-BABY CONDITION Descriptive: cyanosis (1/2) resulting from lack of O2 to cells (1/2) Cause: mainly developmental (non-genetic) (1) failure of foramen ovale to close (1) other circulatory defects (ductus arteriosus, restriction in pulmonary artery) (1/2) mixture of oxygenated & unoxygenated blood (1) lungs bypassed (1/2) Treatment: surgery to close foramen ovale (1) to develop arterial shunt to pulmonary artery (1/2) temporary: increase oxygen tension (1) Detection: respiratory distress noted (1) Prevention cyanosis noted (1/2) abnormal heart sounds noted (1) O2 level monitored with cardiac catheter (1) TAY-SACHS DISEASE Descriptive: neural deterioration, loss of response (1) early death (4 years or younger) (1) mainly in descendents of East European Jewish populations (1/2) Cause: recessive (1/2) mutation (1/2) lack of essential enzyme (1) hexosaminidase A (1/2) accumulation of sphingolipids, etc. (1/2) as intracellular nerve inclusions (1) resulting in interference with normal nerve functions (1) Treatment: none known (1) Detection: enzyme level measured in potential parents to detect heterozygotes (1) Prevention amniocentesis of mothers (1) leading to enzyme assay (1/2) genetic counseling (1/2) possible decision to abort (1/2)
GENETICS QUESTION: 1983 L PETERSON/ECHS State the conclusions reached by Mendel in his work on the inheritance of characteristics. Explain how each of the following deviates from these conclusions: A. Autosomal linkage B. Sex-linked (X-linked) inheritance C. Polygenic (multiple-gene) inheritance STANDARDS: maximum = 15 points total MENDEL (8 points maximum): DISCRETE UNITS 2 FACTORS/TRAIT DOMINANT/RECESSIVE PUNNETT SQUARE: GAMETES HAVE 1 FACTOR EQUAL # GAMETES (EACH TYPE) FACTORS SEGREGATE WHEN GAMETES FORM (SEGREGATION) RANDOM DISTRIBUTION OF FACTORS (INDEPENDENT ASSORTMENT) USE OF PROBABILITY DEVIATIONS (12 points maximum): AUTOSOMAL LINKAGE: DEFINITION (1) EXAMPLE (1) EXPECTED DEVIATION (1) SEX-LINKED: DEFINITION (1) EXAMPLE (1) EXPECTED DEVIATION (1) POLYGENIC: DEFINITION (1) EXAMPLE (1) EXPECTED DEVIATION (1)
GENETICS QUESTION: 1988 L PETERSON/ECHS Discuss Mendel's laws of segregation and independent assortment. Explain how the events of meiosis I account for the observations that led Mendel to formulate these laws. STANDARDS: maximum = 10 points total (no more than 6 points for either part) A. MENDEL'S LAWS FACTORS (genes or alleles) in pairs / 2 alleles per trait (1) FACTORS (alleles, genes) dominant or recessive; or (1) maternal + paternal origin; or (1) heterozygote has 2 types. (1) EXAMPLES (A, a; green, yellow, Punnett square) or monohybrid cross (1) FIRST LAW EXPLAINED: segregation of alleles into gamets (1) SECOND LAW EXPLAINED: independent assortment; each pair assorts independently of other pairs (1) EXAMPLE of dihybrid cross (or Punnett square) (1) ONLY OCCURS WITH UNLINKED GENES; CROSSOVER EXCEPTIONS (1) (max 6) B. MEIOSIS I GAMETES FORMATION (reduction division for purpose of maintaining chromosome #) (1) GENES (traits, alleles) are on chromosomes (1) HOMOLOGOUS CHROMOSOMES PAIR (dyad, bivalent, tetrad used in context) (1) PAIRING OCCURS DURING PROPHASE I (1) SYNAPSIS (synaptonemal complex, chiasmata) (1) may related chiasma to crossover INDEPENDENT ASSORTMENT due to independent alignment at metaphase I (1) PAIRS SEGREGATE AT ANAPHASE I (1) DAUGHTER NUCLEI AFTER MEIOSIS I have one of each chromosome type (each 2 chromatids) (1) (may relate to Punnett square) PHASES OF MEIOSIS I: prophase, metaphase, anaphase, telophase - in correct order some description of each, for example: prophase : organization metaphase : line up at equator anaphase : segregation telophase : 2 "nuclei" (1) (max 6)