genetic disease

Question 1

what is penetrance?

Answer 1

proportion of those that carry the gene will express the trait.

Question 2

what is expressivity?

Answer 2

how the gene is expressed in an individual with same mutation

Question 3

what is a disorder caused by single genes with large effects?

Answer 3

cystic fibrosis and sickle cell anaemia.

Question 4

what type of disorder will be caused by chromosomal disorders?

Answer 4

Downs syndrome.

Question 5

What are complex multigenic disorders?

Answer 5

• gene variants.More than one gene or mutation within a gene associated with conditions.
• each variant has low penetrance and small effect.

Question 6

what are single nucleotide polymorphisms (SNPs)?

Answer 6

change in one nucleotide pair

Question 7

What are contiguous repeats?

Answer 7

dinucleotides
tri (3)
tetra (4)

Question 8

what is a silent mutation?

Answer 8

no change in amino acid sequence

Question 9

what is missense?

Answer 9

change in amino acid sequence

Question 10

what is a nonsense mutation?

Answer 10

premature stop codon

Question 11

what is an amino acid sequence that changes but retains biochemical properties called?

Answer 11

conservative

Question 12

what is the amino acid sequences that is changed but changes biochemical properties?

Answer 12

non conservative.

Question 13

what is frameshift mutation caused by?

Answer 13

insertion and deletion unless it is insertion or deletion of 3 nucleotides.

Question 14

when is a disorder not X-linked?

Answer 14

when passed on from male to male

Question 15

when is a disorder not mitochondrial?

Answer 15

when passed on from male.

Question 16

what does autosomal dominant mutation have?

Answer 16

• variable expressivity despite high penetrance.

- may also have incomplete penetrance

Question 17

what are the key features of autosomal dominant inheritance?

Answer 17

• males and females equally affected.
• unaffected persons do not pass on trait.
• vertical pattern of inheritance with affected individuals in multiple generations.

Question 18

in autosomal dominant inheritance why are homozygotes more severely affected?

Answer 18

there is variable expressivity.

Question 19

what type of disorder or mutation is Marfan’s syndrome caused by?

Answer 19

70-80% autosomal dominant with the remainder De Novo mutations (dna polymerase)

Question 20

in what gene does the mutation for the syndrome occur?

Answer 20

gene FBN1

Question 21

what does Marfan’s syndrome cause to the eye?

Answer 21

Ectopia Lentis slipping of the lens due to weakness of the cilliary zones.

Question 22

what are the key features of autosomal recessive diseases?

Answer 22

• males and females equally affected.
• disorder usually transmitted by two unaffected carrier parents.
• horizontal pattern of inheritance.Found in consanguineous families.

Question 23

How is Stargardts Macular Dystrophy caused?

Answer 23

• ABCA4 mutations
• causes change in ATP binding cassette
• phototransduction cycle affected
• Toxic vitamin A build up in RPE
• Lipofuscin build up.

Question 24

what are the features of x-linked recessive?

Answer 24

• affected males do not transfer to son
• hemizygous males and homozygous females are affected fully.
• vertical transmission of inheritance
• variable expressivity

Question 25

what is lyonization?

Answer 25

in females one x chromosome is inactivated and it could be the healthy one.

Question 26

What is multifactorial inheritance?

Answer 26

incidence of siblings being affected is less than if you have classic mendalian inheritance.
need other environmental factors and mutations.

Question 27

what do structural changes in chromosomes result in?

Answer 27

• rearrangements

- loss of part of chromosome.

Question 28

what do most people who have downs syndrome have it due to?

Answer 28

robertsonian translocation.

Question 29

what are isochromosomes?

Answer 29

chromosomes split in a wrong way

Question 30

what are ring chromosomes?

Answer 30

chromosomes bind and form a ring.

Question 31

what are chromosomal aberrations?

Answer 31

• translocations
• Isochromosomes
• Deletions
• Inversions
• Ring Chromosomes.

Question 32

what are the ocular complications for down’s syndrome?

Answer 32

• refractive errors common
• Hyperopia
• Astigmatism
• Strabismus
• cataracts
• Nystagmus
• Reduced accomodation

Question 33

What does the Fragile X CGC tri-nucleotide repeat in UTR of FMR1 gene lead to?

Answer 33

altered connectivity in CNS leads to mental retardation.

Question 34

What does Leber’s hereditary Optic Neuropathy cause?

Answer 34

• cells with high metabolic demand are affected first
• Optic nerve damage
• Affects mtDNA

Question 35

what is an association study?

Answer 35

not families but populations with and without a disease.

Question 36

How is the Genome Wide Association study done?

Answer 36

• Uses arrays that contain immobilised allele.
• fragmented DNA is fluorescently tagged.
• allowed to hybridise
• fluorescent signal present on SNP chip signifies binding.