Single Gene Disorders

Question 1

What is an Example of Insertion Mutations?

Answer 1

Familial Hypercholesterolemia (FH) results in elevated levels of blood lipids - in Exon 17 of the LDLR gene

Question 2

What is an Example of a Deletion Mutations?

Answer 2

Cystic Fibrosis - deletes Phenylaline (F) residue at 508 in protein on chr 7

Question 3

What is a deletion mutation?

Answer 3

Intron induces aberrant splicing of the DMD gene

Question 4

What is Autosomal Dominant Inheritance?

Answer 4

Characteristic manifested in the heterozygote of both sexes, not linked to a sex chromosome, homozygote is rare with sever phenotype, 50% chance to pass to sibling

Question 5

Who is Affected with ADI?

Answer 5

Both sexes and equally likely to pass on affected characteristic

Question 6

Describe Autosomal Recessive Inheritance?

Answer 6

Characteristic not manifested in heterozygote of both sexes, not linked to sex chromosome, double defect, Affected individual with unaffected parents 25% chance to pass on

Question 7

What is a Compound Heterozygote of ARI?

Answer 7

Refers to an affected individual with 2 different mutant Alleles

Question 8

What is a true homozygotes?

Answer 8

Affected individual from consanguineous relationship then 2 different mutant alleles will be the same

Question 9

What are ARI mutations responsible for?

Answer 9

Lack of gene expression (promoter)
Lack of protein production (frameshift)
Product of protein with absent function (missense AA)

Question 10

Describe X-linked Dominant Inheritance?

Answer 10

Characteristic manifested in heterozygote of both sexes, one parent is affected, more Female than male although show more milder characteristic, 50% chance for child, male unaffected

Question 11

Describe X-linked Recessive Inheritance?

Answer 11

Characteristic is NOT manifested in the heretozygote of both sexes, mostly male born to unaffected parents, sons have 50% change

Question 12

How can Females show affects in X-RI ?

Answer 12

Non-random mosaicism - manifestig heterozygotes

Question 13

What are some examples of X-RI?

Answer 13

Colour blindness, DMD

Question 14

What is Genetic Heterogenity?

Answer 14

Different mutation in the same gene can lead to different disease

Question 15

What is Achondroplasia (dwarfirsm) ?

Answer 15

Gain of function mutation - fibroblast growth factor type 3 receptor unregulated, FGF3R promotes differentiation of cartilige into bain

Question 16

What does the Gain of Function mutation do?

Answer 16

Activates receptor causing premature conversion of the growth plate into bone

Question 17

What can Mutations in 8 different genes that all function to repair damaged DNA lead to?

Answer 17

XP - xeroderma pgmentosum - hypersensitive to sunlight and can develop carcinoma

Question 18

How can Pentrance influence phenotype of single gene disorders?

Answer 18

Frequency with which a person manifests the gene they posses - determined by genetic and environmental factors

Question 19

How can Expressivity influence phenotype of single gene disorders?

Answer 19

Variation in the severity of the symptons caused by a mutation e.g sickle cell anaemia

Question 20

How can Phenocopy influence phenotype of single gene disorders?

Answer 20

Environmental modification mimics a genetic disease, confusing genetic deafness caused by rubella

Question 21

How can Environmental effects influence phenotype of single gene disorders?

Answer 21

Expression of genetic conditions can be influenced by environment e.g Phenylketonuria -low phenylaline diet

Question 22

What type of Tests are carried out for Gene disorders?

Answer 22

Newborn screening
Diagnostic testing
Carrier testing
Prenatal testing