Genetics and Human Disease

Question 1

Pleiotropism

Answer 1

a mutation in a single gene can lead to many effects

Question 2

genetic heterogeneity

Answer 2

a mutation in multiple genetic loci may produce the same trait

Question 3

Autosomal dominant disease

Answer 3

late age of onset

only need one parent to carry defective gene

Question 4

autosomal recessive

Answer 4

earlier age of onset

BOTH parents must carry defective gene

Question 5

Examples of autosomal dominant diseases

Answer 5

1. Huntington’s disease
2. Familial hypercholesterolemia
3. Marfan syndrome

Question 6

Huntington’s disease

Answer 6

triplet repeat on chromosome 4 –> excessive # of glutamine residues –> dysfunctional protein builds up –> toxic to GABA neurons

Question 7

Familial hypercholesterolemia

Answer 7

defective LDL receptor –> very high LDL levels in the blood

Question 8

Marfan syndrome

Answer 8

mutation in fibrillan protein –> weak extracellular matrix

Question 9

Examples of autosomal recessive diseases

Answer 9

1. Phenylketouria (PKU)
2. Cystic fibrosis
3. Sickle Cell Anemia

Question 10

Phenylketouria (PKU)

Answer 10

defective phenylalanine hydroxylase –> phenylalanine is not catabolized –> buildup in CNS causes mental retardation in infants

Question 11

Cystic fibrosis

Answer 11

defective chloride ion channel –> thickened mucus secretions
protects against typhoid

Question 12

Sickle Cell Anemia

Answer 12

defective hemoglobin which precipitates at low O2 tension –> sickling of RBC’s –> buildup and hypoxia

Question 13

X-linked recessive diseases

Answer 13

males most affected

1. hemophilia
2. G6PD deficiency
3. Diabetes insipidus
4. Fragile X Syndrome

Question 14

Hemophilia A & B

Answer 14

defect in clotting factors VIII and IX –> prolonged bleeding due to inability to form fibrin clot

Question 15

Diabetes insipidus

Answer 15

mutation in AVPR2 receptor –> defective vasopressin receptor

Question 16

G6PD deficiency

Answer 16

most common enzyme defect in humans

usually asymptomatic until hemolysis is triggered –> RBC’s unable to repair

Question 17

Fragile X Syndrome

Answer 17

triplet repeat in FMR1 gene

affects brain development

Question 18

Non-dysjunction

Answer 18

chromosomes do not separate normally

Question 19

Examples of diseases from non-dysjunction

Answer 19

1. Down’s syndrome (trisomy 21)
2. Turner’s syndrome (X0)= only one X chromosome
3. Klinefelter’s syndrome (XXY)= extra X

Question 20

positive selection

Answer 20

confers a survival advantage

ex: alcohol tolerance, lactose tolerance
ex. Sickle Cell carriers are protected from malaria, Tay Sach’s protected against TB, Type AB blood resistant against cholera

Question 21

multiple sclerosis

Answer 21

incidence is higher in countries far from the equator (US, Canada, Northern Europe)

Question 22

Venous thrombosis

Answer 22

increased risk in pts who are oral contraceptive users with the Factor V Leiden mutation (majority are AA substitution at position 506) –> makes them more predisposed to having blood clots
most frequent CV event in young women