Gain of Function vs Loss of Function; Recessive vs Dominant Alleles; Autosomal Dominant Inheritance: Achondroplasia, FGFR3, Lethal Homozygotes, Marfan Syndrome, FBN1, Pleiotropy, Neurofibromatosis Type 1, Variable Expressivity, Familial Hypercholesterolem

Gain of Function vs Loss of Function; Recessive vs Dominant Alleles; Autosomal Dominant Inheritance: Achondroplasia, FGFR3, Lethal Homozygotes, Marfan Syndrome, FBN1, Pleiotropy, Neurofibromatosis Type 1, Variable Expressivity, Familial Hypercholesterolemia, LDLR, Retinoblastoma, RB1, Incomplete Penetrance, Li-Fraumeni, Huntington’s Disease, Anticipation; Autosomal Recessive Inheritance: Cystic Fibrosis, CFTR, Allelic Heterogeneity, Tay-Sachs Disease, HexA, Glycogen Storage Disease, PKU, Maple Syrup Urine Disease, Sickle Cell Anemia, Albinism; Dominant Negative Mutations; New/Spontaneous Mutations; Cancer Syndromes Exam Questions Verified and Provided with A+ Graded Rationales Latest Updated 2026 Gain of Function vs. Loss of Function Gain of Function: -Results in production of a protein that has increased activity in unregulated manner Loss of Function: - Results in either lack of protein or synthesis of protein that is non-function Recessive allele vs. Dominant allele Recessive allele: -only expresses phenotype if there are two copies present Dominant allele -expresses phenotype regardless of whether there are 2 copies or only one Autosomal Dominant Inheritance - every generation has 1 member affected - skips NO generations - Males & Females affected equally - father CAN pass to son Achondroplasia "A con dwarf" Autosomal Dominant or Recessive Autosomal Dominant (all generations affected) Achondroplasia (HY/TQ) "A chon dwarf" "Field Goal Friday 3 Pts (think of Jackass)" - Common symptoms -What gene is mutated - What does the gene normally responsible for Which is the lethal phenotype on Punnett square? Dwarfism Gene: Gly380Arg mutation in FGFR3 gene - gain of function - inhibits chondrocyte proliferation - inhibits limb development Homozygous (AA) = LETHAL Presentation: - shortening of limbs - macrocephaly (large head) - lumbar lordosis - trident configuration What is the lethal phenotype for achondroplasia? (HY/TQ) AA - EXCLUDE the lethal one in the percentage EX: out of 3 and not out of 4 What gene is mutated in achondroplasia? FGFR3 (caused by a Gly380Arg mutation) - GAIN of function Marfan's syndrome Autosomal Dominant or Recessive Autosomal dominant Marfan's Syndrome Gene: Fibrillin 1 gene (FBN1 gene) -loss of function - leads to abnormal TGF-B signaling & messes up elastin Symptoms: - aortic root aneurysm - ectopic lentis - tall, abnormally long arms - arachnodactyly What is an example of pleiotropy? (HY) Marfan syndrome - one gene but with LOTS of unrelated effects Neurofibromatosis Autosomal Dominant or Recessive autosomal dominant Neurofibromatosis (HY/TQ) Gene: NF1 gene Symptoms: