144 ■ CHAPTER 08 Chromosomes and Human Genetics
GENETICS
(^12)
3 4 5 6 7 8 9
10
1211
(^1413)
15
16
17
18
19
20
21
22
XY
Huntington disease
Neurodegenerative disorder
tending to strike people in their
forties and fifties
Retinitis pigmentosa
Progressive
degeneration of the
retina
ALD (adrenoleukodystrophy)
Nerve disease portrayed in movie Lorenzo’s Oil
Familial polyposis of the colon
Abnormal tissue growths frequently
leading to cancer
Neurofibromatosis, type 2
Tumors of the auditory nerve and tissues
surrounding the brain
Amyotrophic lateral sclerosis (ALS)
(Lou Gehrig disease)
Fatal degenerative nerve ailment
Adenosine deaminase (ADA)
immune deficiency
Metabolic disorder that damages
the immune system
Amyloidosis
Accumulation in the tissues of an
insoluble fibrillar protein
Breast cancer
Roughly 5% of cases are caused by this
allele
Polycystic kidney disease
Cysts resulting in enlarged kidneys and
renal failure
Tay-Sachs disease
Fatal hereditary disorder involving lipid
metabolism; most common in Ashkenazi
Jews and French Canadians
Familial hypercholesterolemia
Extremely high cholesterol
Spinocerebellar ataxia
Destroys nerves in the brain and
spinal cord, resulting in loss of
muscle control
Cystic fibrosis
Mucus fills up the lungs, interfering
with breathing; one of the most
prevalent genetic diseases in the
U.S.
Multiple exostoses
A disorder of cartilage and bone
Malignant melanoma
Tumors originating in the skin
Multiple endocrine neoplasia, type 2
Tumors in endocrine glands and other
tissues
Sickle-cell disease
Chronic inherited anemia in which red
blood cells sickle (form crescents),
plugging small blood vessels
PKU (phenylketonuria)
An inborn error of metabolism that results
in mental retardation if untreated
Retinoblastoma
Relatively common eye tumor,
accounting for 2% of childhood
malignancies
Burkitt lymphoma
A translocation between
chromosomes 14 and 18 results in
cancer of the white blood cells; most
common in children and young adults
Familial colon cancer
One in 200 people has this allele; of
those who have it, 65% are likely to
develop the disease
Gaucher disease
Chronic enzyme deficiency; fairly
common among Ashkenazi Jews
Figure 8.10
Single-gene disorders
Mutations of single genes that lead to genetic disorders are found on the X chromosome and on each of the 22 autosomes in
humans. In each of these mutations, the healthy allele at that locus codes for an important function; for example, the sickle-cell
allele is a mutation in the gene that codes for the hemoglobin protein, critical for carrying oxygen in the blood. For clarity, only one
such genetic disorder per chromosome is shown.
Q1: Which chromosome contains the gene for cystic fibrosis? For Tay-Sachs disease? For sickle-cell disease?
Q2: No known genetic disorders are encoded on the Y chromosome. Why do you think this is?
Q3: In your own words, explain why most single-gene disorders are recessive rather than dominant.