GEN-02 Genetic Disorders Classification Table

Disorder	Gene	Chromosome	Mutation Type	Inheritance	Key Feature
Sickle cell anaemia	HBB	11	Point mutation (GAG→GUG, Glu→Val pos. 6)	Autosomal recessive	HbS polymerizes under low $O_{2}$ ; sickle RBCs; vaso-occlusion
Beta-thalassemia	HBB	11	Various (reduces HBB expression)	Autosomal recessive	Reduced/absent beta-globin synthesis; severe anaemia
Alpha-thalassemia	HBA1/HBA2	16	Gene deletions	Autosomal recessive	Reduced/absent alpha-globin synthesis; anaemia
PKU	PAH	12	Various (loss of function)	Autosomal recessive	Phenylalanine hydroxylase deficiency; Phe accumulates; intellectual disability
Haemophilia A	F8	X chromosome	Various (F8 loss of function)	X-linked recessive	Clotting factor VIII deficiency; prolonged bleeding; joint swelling
Colour blindness	OPN1LW/OPN1MW	X chromosome	Various	X-linked recessive	Inability to distinguish red from green

Disorder	Karyotype	Chromosome Change	Sex	Total Chr.	Barr Bodies	Key Features
Down syndrome	47, +21	Trisomy 21 (autosome)	M or F	47	0 (M) / 1 (F)	Intellectual disability, epicanthic folds, simian crease, short stature
Turner syndrome	45, XO	Monosomy X (missing sex chr.)	Female	45	0	Short stature, webbed neck, shield chest, infertility, primary amenorrhoea
Klinefelter syndrome	47, XXY	Extra X in male	Male	47	1	Gynaecomastia, tall stature, small testes, reduced fertility
Super Female	47, XXX	Extra X in female	Female	47	2	Often phenotypically normal, may have reduced fertility

Mendelian: single gene mutation, normal chromosome number, detected by DNA/biochemical testing, follows Mendelian ratios
Chromosomal: aneuploidy $\frac{gain}{loss of whole chromosomes}$ , abnormal chromosome count, detected by karyotyping, not inherited in simple Mendelian ratios