Exam 5: Genetics of Development - Principles Flashcards Preview

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Flashcards in Exam 5: Genetics of Development - Principles Deck (56):
1

anterior/posterior axis

first visible structure in embryo
defined by primitive streak, marks groove at which ectodermal cells form 3 germ layers

2

axes in the developing limb

shoulder-to-fingertip is proximal-distal
thumb-to-fifth-finger is anterior-posterior
dorsum-to-palm is dorsal-ventral

3

blastocyst

hollow sphere containing group of cells called inner cell mass
16 cell embryo (morula) transforms into blastocyst

4

chordin

secreted from cells in node and induce dorsal development in concentration-dependent manner

5

clinical dysmorphology

describes etiology of birth defects and gives valuable clues about underlying abnormality in development process

6

deformations

result from extrinsic influence on development of affected tissue
defect from outside
lack of amniotic fluid constrains fetus because not enough room to expand - can lead to contractures of limbs

7

disruptions

destruction of developing tissue
amniotic bands sometimes wrap around developing fetal limbs, choke off their blood supply & tissue is destroyed

8

ectoderm

develops from epiblast
forms skin and nervous system

9

embryonal period of development

after fertilization of an egg, begins with 4 cell divisions without cell growth
lasts from week 1 to week 8

10

endoderm

forms gut and lung epithelium

11

epiblast

formed from inner cell mass
goes on to form the embryo - upper cell layer

12

formin and renal aplasia

mutation in formin gene in mice causes renal aplasia in about 20% of mice
All mice were genetically and environmentally identical - means another cause of reduced penetrance
formin mutation can be tolerated - formin mutation does not cause, but rather increases probability for developing renal aplasia

13

gastrulation

produces primitive streak - first axis of embryo
creates three germ layers - endoderm, mesoderm, and ectoderm

14

homeobox genes (HOX)

determines patterning (division into segments to define part development) along anterior/posterior axis
family of transcription factors - contain homeodomain, a DNA binding domain
4 HOX clusters on 4 chromosomes
expression of each of genes in cluster correlates with position of cell and timing of expression
Each cell along axis experiences different ration of expression of different HOX genes - code for fate of cell

15

homeodomain

DNA binding domain contained in homeobox (HOX) genes

16

inner cell mass

in blastocyst - forms epiblast

17

isolated anomalies

affect a single body region
usually either sporadic or multifactorial
about 60% of major birth defects
i.e. cleft palate

18

major anomalies

anomalies with surgical or cosmetic consequences, like cleft lip or amputated limb

19

minor anomalies

have little impact on well being of patient
give important diagnostic clues about presence of a syndrome

20

malformations

result from intrinsic abnormality in developmental process
defect comes from within

21

mesoderm

form bone, muscles, and most internal organs

22

morula

16 cell embryo
transforms into blastocyst

23

mosaic phase

begins after gastrulation
loss of a cell in this phase cannot be compensated - will lead to loss of tissue
affects baby - removal of cells for screening needs to be done before this phase

24

regulative phase

cells functionally equivalent - loss of a part of embryo can be compensated for by neighboring cell
ends with gastrulation

25

nodal

gene required for formation of primitive streak & later for formation of left/right axis
soluble protein secreted into extracellular space - diffuses through tissue and establishes gradient - NOT a transcription factor (because it can leave the cell)

26

noggin

protein secreted from cells in the node
induce dorsal development in concentration-dependent manner

27

polydactyly

extra digits (in hands/feet)
mutations interfere with developmental process of limbs
originate from defect within affected organ - malformation

28

primitive streak

defines first axis of embryo, produced by gastrulation
marks groove at which ectodermal cells invade space between epiblast and hypoblast to form 3 germ layer

29

Robin sequence

causes cleft palate
extrinsic constraint on fetus (from low amount of amniotic fluid) interferes with growth of jaw - small chin
tongue pushes into forming hard palate & blocks formation - forms u-shaped cleft palate

30

segmental overgrowth

consequence of dysregulation during development - can occur from just one additional cell division per affected cell - loss of control over cell division

31

sequence

cascade of events
starts from isolated anomaly and leads to multiple malformations - usually sporadic or multifactorial
phenotypes caused sequentially by singe defect

32

syndrome

affect several body regions and most often display chromosomal or Mendelian inheritance
present when disease phenotypes are caused by single defect simultaneously

33

situs ambiguus

caused by defects in left/right axis formation
serious condition in which orientation of organs is randomized
usually accompanied by heart defects

34

situs inversus

caused by defects in left/right axis formation
all of organs are in complete mirror image of where normally found
usually asymptomatic

35

Sonic hedgehog (Shh)

signaling protein from notochord (precursor of spine) left/right asymmetry caused by asymmetric expressions of this gene - leads to left side expression of nodal, which initiates left-looping of heart tube

36

Dorsal/ventral axis

specified by noggin and chordin in concentration dependent manner

37

time of implantation

day 7 to 12

38

Treacher-Collins Syndrome

autosomal dominant
small jaw, down slanting palpebral fissuers, malar hypoplasia, cleft palate
risk for complications is high and surgery risky

39

VACTERL association

Vertebral, Anal atresia, Cardiac, Tracheo=Esophagal fistula, Renal and Radial Limb defects)
abnormality that occurs during first 1-4 weeks of development causes multiple major abnormalities in entire embryonic regions
originates from damage to developing mesoderm at 20-25 days after conception
maternal diabetes is a major risk factor

40

Abnormalities occurring from week 5 to 8

affect specific organs & produce single major anomalies - congenital heart defects

41

Abnormalities occurring after week 9

have mild effect on individual

42

What percentage of children are born with a birth defect?

2-3%

43

What is the percentage of mortality of children with birth defects?

20%, most common cause of infant death in US

44

What are the most common birth defects

Heart defects, pyloric stenosis, neural tube defects, orofacial clefts, clubfoot

45

What is the prevalence of heart defects?

1/100 - 1/200 live births

46

What is the prevalence of pyloric stenosis?

1/300

47

What is the prevalence of neural tube defects?

1/1,000

48

What is the prevalence of orofacial clefts?

1/700 - 1/1,000

49

What is the prevalence of club foot?

1/1,000

50

Percentage of birth defects with complex/ multifactorial inheritance

50%, no identifiable cause

51

Percentage of birth defects caused by chromosomal defects

25%

52

Percentage of birth defects caused by single-gene mutations

20%

53

Percentage of birth defects caused by non-genetic factors (maternal medication and infections

5%

54

pre-implantation diagnosis

in morula phase (before mosaic phase) a cell can be removed from embryo and examined for chromosomal aberrations without harming embryo
15 remaining cells develop into normal embryo

55

5 processes by which cells participate in development

Gene regulation by transcription factors and chromatin modification
Cell-cell signaling, either by direct contact or by secretion of morphogens
Development of specific cell shape and polarity
Movement and migration of cells
Programmed cell death

56

robustness

countering of factors capable to disturb orderly development
recognized by cell and regulatory mechanisms used