Patterns of Single Gene Inheritance

Question 1

3 Genetic disorders

Answer 1

1. Single gene (Mendelian disorder)
2. Chromosomal
3. Complex

Question 2

Terms : 1. Allele

Answer 2

Alternative forms of gene/DNA seq

at a specific chr location.

Question 3

2. Polymorphism

Answer 3

Any seq variant that presents

at a frequency of >1% in a population.

Question 4

3. Wild type

Answer 4

Non mutated gene.

Question 5

4. Mutant

Answer 5

Differs from normal by one/more mutation.

Question 6

5. Genotype

Answer 6

Genetic constituent.

Question 7

6. Phenotype

Answer 7

Observable trait.

Question 8

7. Homozygote

Answer 8

2 alleles at given locus are identical.

Question 9

8. Heterozygote

Answer 9

2 alleles at given locus are different.

Question 10

9. Locus

Answer 10

Unique chr location to define a position of gene/DNA sequence.

Question 11

10. Compound heterozygote

Answer 11

Two different mutant alleles at given locus.

Question 12

Dominant

Answer 12

A phenotype expressed in heterozygote.

e.g. Aa

Question 13

Recessive

Answer 13

A phenotype NOT expressed in heterozygote.

e. g. aa
- often enzyme defects.

Question 14

4 patterns of inheritance

Answer 14

1. Autosomal D
2. Autosomal R
3. X-Linked D
4. X-Linked R

Question 15

Autosomal Dominant

Answer 15

1. One parent affected
2. Vertical pattern
3. M & F affected equally
4. M to M transmission possible
5. Child of affected : 50% (heterozygote)
6. Child of non : 50% (homozygote)
7. New mutation possible!

Question 16

AD disorders

Answer 16

1. Familial Adenomatous Polyposis (APC)
2. Huntington Disease (HD)
3. Neurofibromatosis (NF1, NF2)
4. Familial Hypercholesterolaemia (LDLR)
5. Osteogenesis Imperfecta (COL1A1/2)
6. Achondroplasia (FGFR3)
7. Polycystic Kidney Disease (PKD1/2)
8. Marfan Syndrome (FBN1)
9. Hereditary Breast and Ovarian cancer (BRCA1/2)
10. G6PD deficiency

Question 17

Autosomal Recessive

Answer 17

1. 2 mutations
2. Unaffected parents (carriers)
3. NOT present in multiple generation
4. M & F affected equally
5. Children of 2 heterozygous carriers ;
   - Unaffected : Homozygous normal : 25%
   - Affected : Homozygous mutant : 25%
   - Carrier : Heterozygous Asymptomatic : 50%

Question 18

AR disorders

Answer 18

1. Cystic Fibrosis (CFTR)
2. Haemochromatosis (HFE)
3. Tay Sachs (HEX A)
4. Phenylketonurea (PAH)
5. Wilson’s Disease (ATP7B)
6. Sickle Cell Anemia (HBB)

Question 19

X-Linked Dominant

Answer 19

1. Rare
2. Affects either sex but XX&raquo_space; XY
3. Females : More mild cos X inactivation.
4. Affected XmX : 50% child affected
5. Affected XmY : -All daughter affected (Xm)
   - No sons affected (Y)

Question 20

XD disorders

Answer 20

1. Incontinentia Pigmenti (NEMO)
2. Vitamin D Resistant Rickets (VDR)
3. RETT syndrome

Question 21

X-Linked Recessive

Answer 21

1. Mainly MALES (hemizygous, XmY)
2. Female carriers : Asymptomatic, skipped generations
3. Unaffected parents : mother carrier
4. Affected MALE relatives
5. ALL daughters carriers (XmX)
6. If female (XmXm), affected homozygous.
   - uncommon (requires affected father & carrier mother)
   - All SONS affected
   - All daughters carrier
7. If female (XmX), carrier asymptomatic.
   - unaffected unless non random lyonisation.
   - Son : 50% affected
   - Daughter : 50% carrier
8. New mutations possible

Question 22

XR disorders

Answer 22

1. Duchenne Muscular Dystrophy (Dystrophin)
   - Onset : 3-5 yo
   - Death : 20yo
   - 60-65% mutations : Large deletion
2. Haemophilia A

Question 23

Mitochondrial Inheritance

Answer 23

1. Mitochondria inherited from mother thru oocyte.
2. Males & females affected
3. Transmitted thru female line ONLY
4. Brain & muscle disorder

Question 24

Mitochondrial disorders

Answer 24

1. Leber Optic Neuropathy
2. MERRF
3. MELAS syndrome