Chapter 1 ( Single Gene Disorders )

Question 1

When is a generation skipped in autosomal dominant inheritance ?

Answer 1

When there is incomplete penetrance

Question 2

Examples for autosomal dominant diseases ?

Answer 2

Familial hypercholesterolemia 
Huntington disease 
neurofibromatosis type 1
Marfan syndrome 
Acute intermittent porphyria

Question 3

Examples for autosomal recessive diseases ?

Answer 3

Sickle cell anemia
Cystic fibrosis
Phenylketonuria
Tay-Sachs disease

Question 4

Examples of X-linked recessive diseases ?

Answer 4

Duchenne 
Lesch-Nayhan syndrome (HGPRT deficiency )
G6PD deficiency 
Hemophilia A and B 
SCID
Menke’s disease

Question 5

Which regions in Barr Body are not inactivated ?

Answer 5

Tips of both long and short arms

Question 6

What is the primary gene that cause X chromosome inactivation ?

Answer 6

XIST

Question 7

Cause of manifesting heterozygotes females ?

Answer 7

By random chance most of the X chromosomes carrying the normal allele have been inactivated

Question 8

Examples for X-linked dominant diseases ?

Answer 8

Hypophosphatemic rickets
Fragile X syndrome
Alport syndrome

Question 9

Fragile X syndrome ?

Answer 9

Males : 100% penetrance
Symptoms : mental retardation
Large ears and prominent jaws
Macro orchidism

Females : 60% penetrance
Symptoms - mental retardation

Question 10

Function of mitochondrial DNA ?

Answer 10

Encodes proteins that are subunits of complexes in the electron transport and oxidative phosphorylation processes.
It encodes 22 tRNAs and 2 rRNAs

Question 11

Examples for mitochondrial inheritance diseases ?

Answer 11

Leper hereditary optic neuropathy
MELAS ( mitochondrial encephalopathy , lactic acidosis and stroke-like episodes
Myoclonic epilepsy with ragged red muscle fibers

Question 12

Examples for incomplete penetrance ?

Answer 12

Hemochromatosis
Lynch syndrome ( HNPCC)
Retinoblastoma
BRCA1 , BRCA3

Question 13

Marfan syndrome defect ?

Answer 13

Mutation of the gene encoding fibrillin on chromosome 15

Question 14

Example for locus heterogeneity ?

Answer 14

Osteogenesis imperfecta type 2 in which either mutation in a gene in chromosome 17 or in a gene in chromosome 7 can cause the disease

Question 15

Examples for diseases with delayed age of onset ?

Answer 15

Huntington disease
Acute intermittent porphyria
Hemochromatosis
Familia breast cancer

Question 16

Prader-Willi syndrome ?

Answer 16

Papa’s gene (SNRPN)is deleted while mom’s gene is imprinted on chromosome 15 , the affected gene codes for a protein part of spliceosomes
Symptoms : Hyperphagia and Obesity
Hypogonadism
neonatal hypotonia
Poor feeding in neonatal period
Moderate mental and developmental retardation
Small hands and feet

Question 17

Angelman syndrome ?

Answer 17

Mom’s gene (UBE3A) is deleted and papa’s gene is imprinted on chromosome 15 , the affected gene leads to dysfunctional proteasome
Symptoms : sever mental retardation
Seizures
Ataxia
Puppet like posture of limbs and happy disposition

Question 18

Homologous regions in sex chromosomes ?

Answer 18

Pseudo autosomal regions