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Medical Genetics - BL > Single Gene Disorders > Flashcards

Single Gene Disorders Flashcards

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USMLE® Step 1 flashcards Biology 101 flashcards
1
Q

are AD dz alleles common or rare? are AD trait alleles common or rare?

A

dz alleles: rare

trait alleles: common

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2
Q

are AR dz alleles common or rare? are AR trait alleles common or rare?

A

AR dz alleles are common

AR trait alleles are rare

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3
Q

chromosome abn are seen in how many live births and are the leading cause of what?

A

1 in 150 live births

leadings cause of mental retardation and PG loss

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4
Q

what is aneuploidy?

A

deviation from the euploid (cell that has multiple of 23 chromosomes) by chromosome gain or loss

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5
Q

what is euploid?

A

cell that has a multiple of 23 chromosomes

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6
Q

gametes have how many chromosomes and are considered what?

A

23 chromosomes and are considered haploid

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7
Q

how many chromosomes do somatic cells have? they are considered what?

A

46

they are considered diploid

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8
Q

what is the MC autosomal trisomy?

A

trisomy 21 - down’s syndrome

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9
Q

RFs for trisomy 21? increased risk of what cancer w/this dx other effects?

A

increased w/increased maternal age
40% have congenital heart defects
increased risk of ALL
reduced fertility

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10
Q

MC causes of mental retardation?

A

down syndrome
fragile x syndrome
fetal alcohol syndrome

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11
Q

physical characteristics of down syndrome?

A 
flattened nose and face 
upward slanting and eyes
single palmar crease
short 5th finger that curves inward
widely separated first and second toes and increased skin creases on the feet
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12
Q

prognosis of edward syndrome? other name? malformations seen where? heart problems?

A

very poor prognosis, most trisomy 18
most don’t live past birth
AVSD, PDA

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13
Q

physical characteristics of edward syndrome?

A 
hand and foot malformations
low set ears and micrognathia
occiput or back of skull is prominent, dysplastic or malformed ears, clenched hands with overlapping fingers
flexed big toe, prominent heels
small mouth, jaw, short neck
shield chest
short or prominent sternum
wide-set nipples
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14
Q

what is patau syndrome? physical characteristics? prognosis?

A 
trisomy 13
polydactyly
cleft lip, palate
microphthalmia (small eyes)
microcephaly
cardiac and renal defects
very poor prognosis
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15
Q

are babies with autosomal monosomies going to have a good or poor outcome?

A

poor - most are inconsistent with a live birth

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16
Q

what is the only monosomy consistent with life? why is it the only one?

A

turner syndrome 45, X (also 46, XX, 47, XXX)

only one because it’s not autosomal

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17
Q

physical characteristics of turner syndrome?

A

marked short stature, ovarian dysgenesis and neurocognitive problems

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18
Q

can help pts with turner syndrome greater height by injecting with what?

A

growth hormone

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19
Q

what is 47, XXY known as?

A

klinefelter’s syndrome

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20
Q

XXY males are likely to have what health problems?

A

health issues which normally present in women such as breast cancer, thromboembolic disease and osteoporosis

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21
Q

at what stage in replication does klinefelter’s develop?

A

meiosis I

22
Q

what does ‘hypogonadism’ in klinefelter’s refer to?

A

low levels of testicular atrophy with low levels of testosterone and elevated LH:FSH

23
Q

effects of klinefelter’s syndrome?

A

appears over time, not at birth
XXY males have weaker muscles and reduced strength, as they grow older they tend to become taller than average
as teens may have larger breasts, weaker bones, lower E levels than peers

24
Q

fertility of men with klinefelter’s?

A

reduced

25
Q

47, XYY occurs in what stage of cell division?

A

anaphase II of meiosis II

nondisjunction leaves sperm cell with an extra copy of the Y chromosome

26
Q

when do all women’s egg cells form? what stage are they left in then?

A

form during fetal development

remain in suspended meiosis prophase I until ovulation

27
Q

when is nondisjunction more likely to occur?

A 
during oogenesis (over spermatogenesis)
also more likely to occur with increasing maternal age
28
Q

probability of having a baby with down’s syndrome in women less than 30 yo? at age 35? at age 40?

A

1/1000 when less than 30
1/400 at age 35
1/100 at age 40

29
Q

70% of down syndrome cases are identified by what?

A

triple screen (alpha-fetoprotein, chorionic gonadotropin and unconjugated estriol) +/- inhibin A

30
Q

what is the quad test?

A

used to screen for down syndrome
includes: alpha-fetoprotein, HCG, estriol and inhibin A
done btw 15-20 wks of PG

31
Q

what happens in a reciprocal translocation?

A

two non-homologous chromosomes break and exchange fragments

32
Q

reciprocal translocations can cause what?

A

partial trisomies and partial monosomies

33
Q

what is the philadelphia chromosome? it is an example of what?

A

philadelphia chromosome results from translocation of the long arms of chromosomes 9 and 22
reciprocal translocation after birth that affects oncogenes/tumor suppressor genes = cancer can grow more easily

34
Q

if philadelphia chromosome happens in hematopoietic cells what can it result in?

A

CML

35
Q

t (9,22) chromosome translocation causes what?

A

chronic myelogenous leukemia

36
Q

t (15, 17) chromosome translocation causes what?

A

acute myelogenous leukemia

37
Q

t (14, 18) chromosome translocation causes what?

A

follicular lymphoma

38
Q

t (8, 14) chromosome translocation causes what?

A

burkitt’s lymphoma

39
Q

t (11, 14) chromosome translocation causes what?

A

mantle cell lymphoma

40
Q

what is a robertsonian translocation?

A

where both the short arms are lost

41
Q

what happens in down syndrome translocation?

A

long arms of 14 and 21 pair
short arms disappear
3 chromosomes remain

42
Q

what is the chromosomal abn in cri-du-chat?

A

deletion in 46, XX or 46, XY of 5p (deletion of short arm of chromosome 5)

43
Q

what deletion is prader-willi syndrome? what deletion is angelman syndrome?

A

PWS: when there is a microdeletion on dad’s chromosome 15 transmitted to the child
AS: when there is a microdeletion on mom’s chromosome 15 transmitted to the child

44
Q

how does prader-willi present? physical cahracteristics?

A

child has intense craving for food and will do almost anything to get it
can lead to weight gain and morbid obesity
trouble eating as an infant with poor weight gain
delayed motor development
narrow bifrontal skull
rapid weight gain
short stature
slow mental development
very small hands and feet in comparison
often small and floppy infants
male infants may have undescended testicles

45
Q

how does angelman syndrome present? physical characteristics?

A

very happy children!
developmental delays such as lack of crawling or babbling at 6-12 mos and intellectual disability
lack of or minimal speech
inability to walk, move or balance well (ataxia)
trembling movement of arms and legs
frequent smiling and laughing
seizures that begin btw 2-3 yo
stiff or jerky movements
small head size with flatness in the back of the head
strabismus
tongue thrusting
walking with arms up in the air
light pigmentation of the skin, hair and eyes

46
Q

what is inversion?

A

when chromosome segment btw 2 breaks is reinserted in the same location but in reverse order
still retain all of their genetic material so usu unaffected

47
Q

are inversion carriers usu affected?

A

no because they retain all of their genetic material

48
Q

what can a ring chromosome form from?

A

when a deletion occurs on both tips of a chromosome and remaining chromosome ends fuse together

49
Q

how does an isochromosome form?

A

when a chromosome divides along the axis perpendicular to its normal axis of division
two copies of one but no copy of the other chromosome

50
Q

are people w/isochromosomes affected?

A

yes b/c missing a whole chromosome unless involving the X chromosome then possibility to be non-fatal

Medical Genetics - BL (14 decks)

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