Human Genetics

Some Human Genetic Traits and Conditions

Name of Trait	Description (Phenotypes)	Mode of Inheritance	Comments
Ear lobes	free/attached	autosomal dominant	D_=free lobes dd=attached lobes
Tongue rolling	able to roll/not able	autosomal dominant	R_=roll rr=unable to roll
Hairline	widow's peak/straight	autosomal dominant	W_=widow's peak ww=straight line
Freckles	freckles/no freckles	autosomal dominant	F_=freckles ff=no freckles
Eye color	blue to dark brown	autosomal incomplete dominant	BB=dk. brown Bb=lt. brown bb=blue
Skin pigmentation	variable from light to dark	polygenic	model: 3 loci (P, Q, R) from ppqqrr=lightest to PPQQRR=darkest
Stature	variable normal height	polygenic	a 6 loci model is one
ABO blood groups	Type A, B, AB, & O	autosomal codominant multiple alleles	ii= type O I^AI^A or I^Ai= type A I^BI^B or I^Bi = type B I^AI^B=type AB
Rh blood groups	Rh factor on RBC (Rh-positive)/ Rh factor not on RBC (Rh-negative)	autosomal dominant	Rh_=Rh-positive rhrh=Rh-negative
Color blindness	inability to distinguish red from green	sex-linked recessive	1/12 males 1/250 females X^CX^C or X^CX^c = normal vision female X^cX^c = color blind female X^CY = normal vision male X^cY = color blind male Info on color blindness
Hypertrichosis	hair on edge of ear pinna, males only	Y-linked	XYH = hairy eared XYh = not
Pattern baldness	M-shaped hairline receding with age	complex, sex influenced	BB = bald male, thin hair female Bb = bald male, full hair female bb = full head of hair in both sexes
Polydactyly	extra fingers or toes	autosomal dominant with reduced penetrance (90%)	P_ = extra fingers or toes pp = 5 fingers and 5 toes on each appendage

Condition	Description (phenotype)	Mode of Inheritance	Comments	Information Links
Tay-Sachs disease	degeneration of the nervous system in infancy, fatal. "amaurotic idiocy"	autosomal recessive	1/3600 central European Jews T_ = normal tt = disease [Tt = "carrier"]	National Tay-Sachs and Allied Diseases Association
Cystic fibrosis	chloride channels defective; mucus secretion in lungs	autosomal recessive	1/2500 in Caucasians C_ = normal cc = disease	Cystic Fibrosis Foundation
Sickle-cell disease	severe anemic disease	autosomal incomplete dominant	1/400 African-Americans SS = anemia SS' = "trait" S'S' = normal	The Sickle Cell Information Center
Achondroplasia	dwarfism (one kind)	autosomal dominant	1/10,000 AA = lethal (stillborn) Aa = dwarf aa = normal stature
Huntington's Disease	mental deterioration (onset in middle age)	autosomal dominant	1/25,000 H_ = disease hh = normal	Huntington's Disease Society of America
Hemophilia	slow clotting of blood	sex-linked recessive	X^HX^H or X^HX^h = normal female X^hX^h = hemophiliac female X^HY = normal male X^hY = hemophiliac male	National Hemophilia Foundation
Albinism	absence of pigmentation in skin, eyes & hair	autosomal recessive	A_ = normal pigmentation aa = albino	The National Organization for Albinism and Hypopigmentation
Phenylketonuria (PKU)	lacking enzyme to convert phenylalanine to tyrosine, results in severe retardation	autosomal recessive	P_= normal pp = PKU	PKU News
Alkaptonuria	blue-black cartilage, urine, arthritis	autosomal recessive	K_= normal kk = alkaptonuria
Genetic Goitrous Cretinism	mental retardation, slow growth; treated by replacement;lacking enzyme to convert tyrosine ultimately to thryroid hormone	autosomal recessive	C_ = normal cc = cretinism
Tyrosinosis	accumulates tyrosine	autosomal recessive
Duchenne Muscular Dystrophy	progressive weakening of muscles and lost of coordination	sex-linked recessive	1/3500 males X^DX^D or X^DX^d = normal female X^dX^d = dystrophic female X^DY = normal male X^dY = dystrophic male