genetic testing

Question 1

karyotype

Answer 1

looking at whole chromosomes for balanced or unbalanced translocations, aneuploidy, large imbalances

Question 2

SNP microarray (uses either comparative genomic hybridisation - comparing to a control) or SNP -

Answer 2

looks at the amount (too little, too much or just enough) of DNA material. compared to a control (T21 or 22q11, williams)

SNP: specific probes at each point of a chromosome to detect and record hybridization signal, can detect same as above but not uniparental disomy (the bit that should be there just won’t be there)

Question 3

FISH

Answer 3

presence or absence of specific DNA sequences - submicroscopic chromosomal. specifically microdeletions (22.q.11), if you liik for it you can find it (need spefici target and only finds those target things)

Question 4

what can SNP NOT detect?

Answer 4

balanced rearrangements, triplet repeats, sequence changes, methylation changes, whole/partial gene duplications

Question 5

sanger sequencing

Answer 5

exact DNA sequence of bases of a gene, can detect single gene mutations (i.e. NOONAN (PTPN11) marfans, NF1,
cannot detect exonic deletons or duplications

Question 6

single gene sequencing

Answer 6

looking for a specific gene - FBN1, NF1

Question 7

triplet repeat analysis

Answer 7

does the number of triplet repeats exceed the normal/stabel threshold?

Question 8

name the 5 triplet repeat disorders and thier triplets

Answer 8

fragile x - CGG
huntington - CAG, spinocerebellar ataxia: CAG, frederich ataxia GAA, myotonic dystrophy - CTG (the baby monitor, just like you squeeze the mum’s hand)

Question 9

carrier risk is 1:25 what is the risk the diamond is affected?

Answer 9

“one in three siblings, one in three siblings”

1/3 x 1/25 = 3/75

3:75

Question 10

what is the incidence of a recessive condition?

carrier frequency is 1:100

Answer 10

square the carrier frequency and multiply by 4

100²x4 = 40 000

incidence is 1 in 40 000

Question 11

what is the carrier frequency if the incidence is 2500?

Answer 11

sq root 2500

=625

625/4

= 25

1:25

Question 12

if no affected siblings in an autosomal recessive condition, what is the likelihood of carrier status?

Answer 12

1/2

Question 13

Autosomal Recessive disorders

Answer 13

deafness, albinism, wilson, sickle cell, thalassemia, CF, Frederich Ataxia, Haemochromotosis, PKU, alpha 1 anti trypsin, homocysteinuria

Question 14

what is pseudodominant in an AR condition?

Answer 14

Recessive condition in >1 generation by bad luck

Question 15

x linked conditions: who is a carrier, who is affected?

Answer 15

half boys from the maternal side

half boys from matrnal side

every girl is an obligate carrier from paternal side

no boy is affected from paternal side

Question 16

x linked recessive mothers

Answer 16

1:4 risk of affected male child in each pregnancy from a female carrier

Question 17

x linked dominant

Answer 17

when females are affected

Question 18

x linked recessive disorders

Answer 18

Haemophillia A, G6PD, Fabry, Ocular albanism, chronic granulomatous disease, fragile x, r, colour blindness, duchenne muscular dystrophym

Question 19

x linked dominant disorders

Answer 19

hypophosphatemic rickets, Rett syndrome, incontientia pigmenti

often lethal in males (survivors are mosaic), males are hemizygous

Question 20

how could a female exprexx phenotypic traits for an x-linked recessive condition?

Answer 20

skewed x linked inactivation

Question 21

imprinting chant

Answer 21

maternal imprinting,

maternal gene silecing

Paternal imprinting,

Paternal gene silencing

Question 22

what is imprinting?

Answer 22

methylation (transcription silencing - methylaion turns off) and histone modification (chromatin - DNA more tightly wrapped, in this conformation is less open to transcription and therefore less mRNA and protein produced histones - more difficult to open histone and transcribe.

the gener of the parent of origin is the important not the gender of the child.

imprinting happens in the genesis of the sperm, or eggs, not the genesis of the baby.

the disorder occurs when there are 2 copies of the active or inactive gene. no good.

Question 23

angelMan

Prader-willi

Answer 23

loss of Maternal 15q11.2-q13 (AngelMan)

loss of Paternal 15q11.2-q13

Question 24

examples of autosomal dominant conditions

Answer 24

familial hypercholesterolaemia

marfan syndrome

adult polycystic kidneys

huntington disease

neurofibromatosis

tuberus scleroris

myotonic dystrophy

von willebrand disease

osteogenesis imperfecta

acute intermittend porphoria

hereditary haemoragghic telangctasia

noonan syndrome

spheroctosis

Question 25

inhertiance of achondroplasia?

Answer 25

Achondroplasia is inherited in an autosomal dominant pattern, which means one copy of the altered gene in each cell is sufficient to cause the disorder. About 80 percent of people with achondroplasia have average-size parents; these cases result from new mutations in the FGFR3