1. Single Gene Inheritance
Human Genetic Disorders

2. Rules that explain inheritance through a family
Modes of Inheritance
Rules that explain inheritance through a family
Autosomal Dominant
Autosomal Recessive
Sex-Linked

3. Autosomal Recessive Can appear in either sex, parents must be carriers
Affected individual is homozygous recessive (nn)
N n N NN Nn
25 % inheritance n Nn nn

4. Cystic Fibrosis Northern Europeans, 1:2000 30, 000 active cases in US
Defective CFTR prevents
chloride ions from moving into
and out of cells, causes a build
up of thick mucus
Affects the lungs, pancreas, sweat glands
Life expectancy depends some may live to be in their 30’s

5. Sickle Cell Disease Chromosome 11 affected
African Americans 1:500 disease, 1:12
carry the allele
Chromosome 11 affected
Gene produces hemoglobin, in sickle cell
disease it is made incorrectly causing the
red blood cells to become sickle shaped
Abnormal cells clump clogging capillaries
Cells cannot transport oxygen efficiently

6. Sickle Cell Continued Codominance
Carriers have some normal and some defective cells
Carriers and those with the disease are resistant to malaria
Codominance

7. Tay - Sachs Disease Orthodox Jewish 1:27 Chromosome 15 affected
Mutation prevents the formation of an enzyme needed to breakdown nervous tissue waste products
Leads to blindness, dementia, loss of muscle function
Children die by age 4

8. Autosomal Dominant
Can appear in any sex, if child has the trait than one parent must have the trait.
Affected individual can be homozygous dominant or heterozygous.
NN or Nn N n n Nn nn
50 % inheritance if one parent affected n Nn nn

9. Achondroplasia Dwarfism Disorder of bone growth
Most cases due to spontaneous mutation
Homozygous dominant individuals die within a few months

10. Familial Hypercholesterolemia
High cholesterol, 1:500
Defective liver cell surface receptors that
normally regulate uptake of cholesterol from the blood
2 defective alleles = no receptors
1 defective allele = 1/2 receptors
no defective alleles = normal receptors

11. Huntington Disease
Nervous system disorder that usually begins to show symptoms at 40 yrs
Leads to brain damage individual dies with 10 yrs
No individual is born with 2 dominant alleles

12. Polydactyly / Syndactyly

13. Marfan Syndrome

14. Lactose Intolerance

15. Lethal Alleles
Some genetic disorders cause a fetus to be miscarried when they inherit 2 dominant alleles
This is called lethal alleles
Huntington
Achondroplasia
Polydactyly