Sex Determination, SRY Gene, X-Linked Dominant Inheritance, Rett Syndrome, Fragile X Syndrome, Vitamin D-Resistant Rickets, X-Linked Recessive Inheritance, Duchenne Muscular Dystrophy, Becker Muscular Dystrophy, Hemophilia A, G6PD Deficiency, Lesch-Nyhan

Sex Determination, SRY Gene, X-Linked Dominant Inheritance, Rett Syndrome, Fragile X Syndrome, Vitamin D-Resistant Rickets, X-Linked Recessive Inheritance, Duchenne Muscular Dystrophy, Becker Muscular Dystrophy, Hemophilia A, G6PD Deficiency, Lesch-Nyhan Syndrome, Red-Green Color Blindness, Menkes Disease, OTC Deficiency, SCID, Manifesting Heterozygous Females, X Inactivation, XIST Gene, Barr Body, Mosaicism, Mitochondrial Inheritance, Heteroplasmy, Leber Hereditary Optic Neuropathy, MERRF, MELAS, Leigh Syndrome, Encephalopathy, Myopathy, Ataxia Exam Questions Verified and Provided with A+ Graded Rationales Latest Updated 2026 Helpful Flow Chart Which gamete determines the sex of the offspring? male gamete (sperm) - contains the SRY gene **females can only give X Sex-linked inheritance Inheritance pattern of a disease that is caused by mutation of a gene present on the X chromosome Can be either dominant or recessive X-linked dominant inheritance Seen in successive generation with at least one affected individual per generation - All females of the affected father are diseased. - Males CANNOT pass to sons "Dad to Daughter = Dominant" ALWAYS What are the X-linked dominant diseases? I would be a Rhett (Wreck) and Fragile without the Vitamin D (the D) Rhett Syndrome Vitamin D-resistant rickets Fragile X Syndrome Rett Syndrome What gene is mutated in Rett syndrome? Is it X-linked Dominant or Recessive? Think Mother Connie (MECP2) would be a Rhett w/o Papa William Gene: MECP2 - without this gene, then genes are inappropriately expressed during brain development (normally acts as a repressor & binds methylated DNA) LETHAL IN MALES Presentation: - spastic/ataxic - autistic behavior - Flapping of hands - microcephaly - seizures - mental deterioration X-LINKED DOMINANT Vitamin D-Resistant Ricketts (Hereditary Hypophosphosphatemic Rickets) What gene is mutated in this syndrome? Is it X-linked Dominant or Recessive? Mnemonic: PHX is hot so you'll get lots of Vitamin D from the sun Gene: PHEX gene mutation - low serum phosphate Presentation: - slow growth - short stature - bone abnormalities - hypophosphatemia X-LINKED DOMINANT Fragile X syndrome (HY) "Formally Fragile" Gene: increase in CGG repeats of FMR1 gene (less mRNA made) - causes inc. in methylation @ the promoter, decrease transcription of the gene Presentation: - intellectual disability (ADD-like) - prominent jaw - large ears - long narrow face X-LINKED DOMINANT X-linked Recessive inheritance - Males are affected more (only one X) - affected fathers pass mutation to ALL daughters and make them carriers - no father to son - Affected sons receive from mother's Which sex does x-linked recessive inheritance effect more? MALES