Cause / The mutant allele in the gene pair is dominant / Both alleles in the gene pair are mutant / The mutant gene is on the X chromosome / Traits produced from several genes acting together / Excess or lack of chromosomal material that is numerical or structural
Heredity / Only one parent must carry the mutant gene. / Typically, both parents carry the mutant gene. 25% chance that any child will inherit the mutation. / One or both parents must carry the mutant gene, which appears on the X chromosome / Difficult to estimate
Distribution / Equal distribution between males and females / Equal distribution between males and females / Males are typically affected because they only have one X chromosome. Females are typically carriers. / Difficult to estimate
Additional Information / If a female has a mutant gene on only one of her X chromosomes, the dominant, normal X gene will be expressed. The recessive condition is only expressed when the entire gene pair is defective.
If a male has a mutant gene on the X chromosome it is always expressed because there is no normal opposing gene. / May involve environmental factors (multifactorial inheritance)
Breast cancer susceptibility has been found on chromosomes 6, 11, 13, 14, 15, 17 and 22. / May involve environmental factors: radiation, chemicals, viruses
Trisomy – a chromosome from any of the pairs may be duplicated
Monosomy – a chromosome from any of the pairs may be absent
Disorders / Marfan Syndrome, Otosclerosis, Machado-Joseph Disease / Cystic Fibrosis, Sickle Cell Anemia, Tay Sachs / Color blindness, Muscular Dystrophy, Hemophilia / Common chronic disorders: Heart Disease, High Blood Pressure, Alzheimer’s, Arthritis, Diabetes, Cancer, Obesity / Trisomy 21, Turner Syndrome, Williams Syndrome, Klinefelter’s Syndrome
Autosome – any chromosome that is not a sex chromosome. 22 of the 23 pairs of chromosomes in a healthy human are autosomes.