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BECOM II Exam 4 > Genetic Mechanisms I&II > Flashcards

Genetic Mechanisms I&II Flashcards

1
Q

trisomy 21, 18, 13

A

only autosomal trisomies that can occur in nonmosaic form & have viable births
-very gene poor

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2
Q

trisomy 21

A
  • most gene poor –> least severe
  • more live births
  • palmar crease, extra skin on hand, epicanthal folds, heart problems (AV canal & VSD)
  • 55 year life expectancy
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3
Q

trisomy 13

A
  • less gene poor –> most severe
  • less live births
  • rocker bottom feet, microcephaly,
  • die w/I 1st month or year
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4
Q

trisomy 18

A
  • prenatal growth deficiency, low birth rate, rocker bottom feet, heart problems (VSD)
  • die w/I 1st month or year
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5
Q

Down syndrome

A
  • trisomy 21 causes 90% of cases

- also caused by: Robertsonian translocation, 21q21q translocation, or partial trisomy 21

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6
Q

balanced vs unbalanced translocations

A
  • balanced –> no loss of genetic material

- unbalanced –> loss of genetic material

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7
Q

risk of Down syndrome or other trisomy

A

risks increase after 35 y/o, but most are born in women under 35 y/o

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8
Q

trisomy 21 in Down syndrome

A

extra copy of 21st chromosome

-random chance parents will have Down syndrome kid

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9
Q

Robertsonian translocation in Down syndrome

A

translocation b/w 21q and 14 or 22

  • does not alter phenotype
  • translocation came from one of the parents (one of them has 45 chromosomes) –> high chance of having another child w/ Down syndrome
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10
Q

21q21q in Down syndrome

A

fusion of chromosome 21 in parents to make single chromosome
-offspring will have mono or trisomies

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11
Q

partial trisomy 21

A

extra copy of part of chromosome 21

-help identify genes responsible and therapeutics

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12
Q

DiGeorge Syndrome

A

micro deletion due to haploinsufficiency

  • craniofacial problems, intellectual disability, heart problems, immune deficient
  • TBX1 in CHD
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13
Q

what causes duplication syndromes?

A

abnormal crossing over –> one chromosome will have more genetic material than other
2 kinds of duplication syndromes
-22q11.2 (swapped evenly)
-cat eye syndrome (duplication and inversion)

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14
Q

idiopathic chromosome abnormalities

A

don’t know exactly where problem is occurring

ex. Cri du chat
- 13 chromosome deletion (deletion varies) –> variable phenotype
- increased eye distance, skin fold of eye lid, jaw behind other
- degree of disability correlates w/ size of deletion

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15
Q

sex chromosomes

A
  • different from autosomes
  • sex determination in distinct steps
  • sexual development disorders if chromosomal sex does not line up with gonadal sex
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16
Q

Y chromosome

A

can also undergo recombination with X chromosome –> pseudoautosomal genes

  • SRY determines male –> defects lead to abnormal devel. & knock out TFs
  • gene poor –> 2 dozen for gonadal/genital devel.
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17
Q

micro deletions of Yq

A

low sperm count to no sperm production

-nonobstructive azoospermia to oligospermia

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18
Q

AZF region (azoospermia factors)

A

important for spermatogenesis

  • mutations leads to low sperm count or no sperm
  • ADZ genes (deleted in azoospermia)
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19
Q

X chromosome

A

Aneuploidy of X chromosome - most common abnormality

  • females - Barr body –> X chromosome inactivates one X keeping other one active
  • males - no Barr body bc only X is active
  • structurally abnormal X almost always inactive (secondary selection)
  • not all genes from inactive X are inactive
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20
Q

klinefelter syndrome (male)

A

XXY

-low sperm count, lack of maturity, small genitalia

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21
Q

47 XXY (male)

A

taller, intellectual delays, ADHD

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22
Q

Turner syndrome (female)

A

one X

-webbed neck, short, edema

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23
Q

trisomy X

A

developmental delays

-increasing severity with increasing Xs

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24
Q

loss of function mutation in SRY or SOX9 in males

A

go down female pathway –> XY gonadal dysgenesis

25
Q

extra SRY or SOX9 in XX individual

A

go down male developmental pathway –> XX testicular or XX ovotesticular disorder

  • SRY –> testicular disorder
  • SOX9 –> ovotesticular
26
Q

mutations in CAIS or PAIS

A

occur during puberty

  • incomplete masculinization
  • have testes but switch to female characteristics
27
Q

mutations in CAH

A

occur during puberty

  • XX virilization
  • have ovaries but switch to male characteristics
28
Q

congenital adrenal hyperplasia

A

virilization of 46, XX infants

29
Q

androgen insensitivity syndrome

A

incomplete masculinization of 46, XY infants

30
Q

neurodevelopmental disorders and intellectual disability

A

hard to determine genetic cause

-genetic unbalanced translocations –> genomic imbalances with intellectual disability and autism

31
Q

X-linked intellectual disability

A

caused by mutations, micro deletions, and duplications

-fragile X syndrome –> FMR1 mutation (CGG repeat)

32
Q

DNA methyltransferase

A

adds methyl group to 5’C of cytosine

  • DNA into heterochromatin (packed more tightly) which silences expression
  • can be passed on during cell division
33
Q

role of methylation

A
  • silence gene expression

- recruitment of HDAC to turn off genes

34
Q

HATs (histone acetylases)

A

transfer acetyl group to remove positive charge on lysine –> DNA loosely packed –> accessible to TFs

35
Q

HDACs (histone deacetylases)

A

restore positive charge on lysine –> DNA tightly packed –> less accessible to TFs
-drugs for HDAC inhibitors

36
Q

role of epigenetics

A

modification to expression pattern of DNA w/o altering bases
-how environment and genotype change phenotype leading to disease

37
Q

genomic imprinting

A

regulatory system where a single allele is expressed and is always parent specific
-beneficial even though you are more susceptible to disorders

38
Q

paternal imprinting

A

growth promoting for offspring - produce more powerful individuals
-silenced growth limiting genes

39
Q

maternal imprinting

A

growth limiting for offspring

-silenced growth promoting genes

40
Q

Prader-Willi syndrome

A

paternal transmission when having mutation

-maternal copy is silenced & does not affect offspring

41
Q

angelman syndrome

A

maternal transmission when having mutation

-paternal copy is silenced

42
Q

epigenetic regulatory system

A

1st generation imprints passed on from gonads of mother and father –> go through cell division of somatic cells –> imprints erased w/I germ cells of embryonic gonad –> imprints reestablished based on sex of embryo

  • if male, pass paternal imprints through testes (prenatally)
  • if female, pass maternal imprints through egg (postnatally)
43
Q

why is methylation used in imprinting?

A

can be passed on (maintainable) and erased

44
Q

how is methylation passed on?

A

Dnmt3 methylates unmethylated DNA –> replication –> hemimethylation –> Dnmt1 completes methylation of hemimethylated strands

45
Q

how is methylation removed?

A
  • erased by passive dilution on maternal chromosomes

- erased by active demethylation via Tet protein on paternal chromosomes

46
Q

mutations in Dmnt3 and Dmnt1

A

alterations in imprinted gene regions

47
Q

imprinted genes and imprint control elements

A

imprint genes usually packed together –> lead to a RNA, not protein

  • methylation/imprinting occurs at DMR or ICE
  • imprinted protein coding genes expressed on same parental chromosome & lncRNA expressed from opposite parental chromosome
48
Q

imprint control elements

A
  • imprinting/methylation of DMR or ICE –> inhibit IG-NC –> expression of protein coding
  • no expression of protein coding w/o imprinting bc the IG-NC will not be inhibited
  • non-imprinted gene always expressed
49
Q

deletion of DMR control region in imprinted chromosome

A

no change in gene expression

-still get protein coding gene and silence non-coding

50
Q

deletion of DMR control region in non imprinted chromosome

A

change to imprinted gene

-get protein coding gene and silence non-coding

51
Q

insulator model of imprinting

A
  • CTCF is the insulator for maternal copy –> binds to ICE –> blocks promoter enhancer interaction –> inhibit protein coding expression
  • in paternal copy –> methylation/imprinting occurs –> inhibit CTCF binding –> silence long noncoding –> promoter enhancer interaction –> expression of protein coding
  • activate paternal copy, inhibit maternal
  • depends on protein to block promoter enhancer interaction
52
Q

long coding RNA model of imprinting

A
  • maternal copy methylated/imprinted –> silence long noncoding –> express protein coding gene
  • paternal copy –> no methylation/imprinting –> Airn NC silences protein coding genes
  • activate maternal, silence paternal
  • depends on RNA to silence protein coding
53
Q

beckwith-wiedemann syndrome

A
  • somatic overgrowth
  • embryologic malignancies
  • increase organ size
54
Q

silver Russell syndrome

A

growth retardation

short stature

55
Q

what is IGF2?

A

a growth factor

-overexpression leads to excess growth

56
Q

what is CDKNC1?

A

cell cycle regulator

  • inhibitor of G1 cyclin/cdk complexes
  • deficiency leads to overgrowth
57
Q

beckwith-wiedemann syndrome genomic imprinting

A
  • maternal chromosome –> CTCF binding to to iGF2 cluster on ICR1 –> no inhibition on H19 (noncoding) –> no expression of Igf2 gene (no protein coding)
  • paternal chromosome –> methylation/imprinting of ICR1 –> inhibition of H19 noncoding –> expression of Igf2 (protein coding)
  • Igf2 comes from paternal, silenced on maternal
58
Q

silver Russell syndrome

A

loss of paternal ICR1 methylation

  • maternal chromosome –> methylation of ICR2 –> silence noncoding (KCNQ1) –> express protein coding (CDKN1C)
  • paternal chromosome –> no methylation of ICR2 –> expression of noncoding (KCNQ1) –> silence protein coding (CDKN1C)
  • CDKN1C comes from maternal, silenced on paternal

BECOM II Exam 4 (10 decks)

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