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BM108 🧬 > development and metazoan body plan 👂 > Flashcards

development and metazoan body plan 👂 Flashcards

1
Q

what is a metazoan?

A

its a type of eukaryotic organism which is a multicellular animal which has specialised for a particular function

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2
Q

what is bilateral symmery?

A

its associated with cephalisation (differentiation of a head)
it is advantageous for organisms moving head first and is elongation along the anteriorposterior axis

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3
Q

why was the evolution of a body cavity important?

A

for isolation, as if organs for phisiological independance: kidney function different from liver
it also allows flexibility when moving so organs dont rip apart
it also prevents organs from sticking to each other: cells like to intermingle

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4
Q

what are examples of body cavities?

A

the gut- forms during the process of gastrulation
pseudocoel/ coelom- theyre fluid filled body cavities that cushion organs and provide them with support

the bosy plan and its cavities are made up of 3 ‘germ layers’ = tissue lineages

  • endoderm
  • mesoderm
  • ectoderm
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5
Q

what are the major cell types?

A
  • epithelial tissues
  • mesenchymal/ connective tissue
  • muscle tissues
  • nervous tissue
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6
Q

what are the three types of body plans?

A

acoelomates - have no body cavity

pseudocelomates - have a body cavity between the mesoderm and endoderm

coelomates - have a body cavity entirely within the mesoderm (called the coelom)

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7
Q

what are the steps of part 1 of embryonic development?

A
  • making stem cells
  • cleavage
  • blastocyst
  • pluripotent stem cells
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8
Q

what does making stem cells do?

A

it restores the diploid genome and begins the process of wiping out the memory of our parents-resetting the clock/ starting afresh

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9
Q

what is cleavage in embryonic development?

A

this is the division of cells in the early embryo
it undergoes rapid cell divisions with NO significant growth
it produces a cluster of cells the same size as the original ‘zygote’

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10
Q

what is a blastocyst?

A

its a structure containing 128 cells with an inner mass or ‘embryoblast’ (forms the embryo proper and embryonic stem cells) and an outer cell mass (goes on to form the placenta)

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11
Q

what are pluripotent stem cells?

A

they’re a type of stem cell that can theoretically give rise to every type of cell in the animal body
they proliferate indefinitely and first recognised in tetocarcinomas

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12
Q

what is part 2 of embryonic development?

A

-its breaking symmetry and implantation

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13
Q

what occurs in inplantation?

A
  • the blastocyst ‘hatches’ by shedding its outer layer
  • this then exposes the bare trophoblast cells to the uterine wall (on day 7)
  • the uterine wall is prepared for implantation each month NY hormonal control
  • the trophoblast begins to thicken as it starts to implant and forms the placenta
  • at 10 days, the embryo is fully implanted
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14
Q

what are the steps in part 3 of embryonic development?

A

making 2 bast cell layers and gastrulation

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15
Q

what are the three ‘germ’ tissues?

A
  • ecoderm
  • mesoderm
  • endoderm
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16
Q

what happens when making 2 blast cell layers?

A
  • the amniotic cavity formation and the appearance of 2 cell layers
  • the inner cell mass (ICM) pulls away from the trophoblast, forming a hollow amniotic cavity
  • the ICM forms a flat disc with 2 layers, the epiblast (dorsal, next to the amniotic cavity) and the hypoblast (ventral, facing the yolk sac)
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17
Q

what is gasturlation?

A
  • it is a step in part 3 of embryonic development where the cell layers (-derms) and body shape are defined
  • some epiblast cells begin to migrate towards the primitive steak
  • then they move through the layer towards the hypoblast- the first cells through form the definitive endoderm then the ones after those form the mesoderm which is an intermediate layer
  • this movement progresses tail to head (caudal to cranial)
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18
Q

what happens in part 4 of embryonic development?

A

part 4 is notochord formation

this is a rod defining the body axis and is the future site of the vertebral column

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19
Q

what is part 5 of embryonic development?

A

it is neurulation

  • this is how the brain and spine form
  • the notochord includes a fold in the overlying epiblast/ ectoderm which pinches off to form a neural tube
  • notochord signals overlying ectoderm to become neural plate, then to neural tube - pinched off into body
  • neural groove formation
  • associated neural crest cells
  • mesoderm begins to differentiate next to notochord three regions
20
Q

what are the types of differentiated mesoderm next to notochord three regions?

A

somites - 40 pairs of body segments by the end of week 4
intermediate mesoderm - just lateral somites
lateral plates - splits to form coelom (body cavity)

21
Q

what is part 6 of embryonic development?

A

neural crest and somite formation and segmentation

  • this is where the closure of the neural tube begins (end of week 3 - end of week 4)
  • neural crest cells form sensory nerves and other structures
22
Q

what is the name of the condition caused by an incomplete neural tube closure?

A

spina bifida

23
Q

what is the most effective way to prevent spina bifida?

A

to take folic acid supplements before and during pregnancy

24
Q

how are developmental processes controlled?

A

by:

  • cell differentiation
  • tissue differentiation
  • cell interactions
  • morphogen gradients
25
Q

what is cell differentiation?

A
  • they start as pluripotent stem cells and over time become more specialised until they reach their terminally differentiated form such as heart muscle, neuron, liver cells etc
  • theres a programmed path to their specified form/ fate
  • this is normally a one-way road
  • each cell has all the information and ability to become the adult organism
  • transplanted cells adopt the form appropriate for their new home
  • early in cell development, cells haven’t been programmed, then later, cells taken from specific places in the body only have the ability to differentiate into cells from that section of the body
26
Q

what are the processes in tissue differentiation that occur?

A
  • local cellular interactions that organise tissues
  • long-range morphogen signals that determine the orientation of the embryo and its specific regions
  • cellular responses to these two types of signals (the ones that cause migration and specific differentiation processes) are irreversibly started
27
Q

what happens in cell interactions?

A
  • mixtures of different cell types organise into regional embryo-like structures, sorting like-with-like cells
  • cell adhesion helps with this and proteins expressed on the surface of cells that like to stick to the same molecules on other cells (homophilic)
28
Q

what are morphogen gradients?

A

morphgen- a secreted molecule that induces fate decisions in recipient cells in a concentration gradient
its a dependant long-range manner

29
Q

what do morphogen gradients require?

A
  • production from a point source
  • long-range distribution
  • reception and interpretation (this is context dependant) by a cell
30
Q

what is wolperts ‘french flag’ model 1?

A
  • in this model, cells can sense the quantity of morphogen and compare it to 2 programmed thresholds and respond in a level with specific differentiation/ behaviours
31
Q

what is wolpert’s ‘french flag’ model 2?

A

its the same idea as model 1 but yes/no logic response of cells

32
Q

what are is the molecular understanding of morphogen effects on anterior-posterior patterning of the limb?

A
  • the ‘zone of polarising activity’ (XPA) secretes a morphogen that sets up the thumb-to-finger organisation
    when ZPA is grafted to the anterior limb bud mesoderm, duplicated digits emerge as a mirror image of the normal digits
    shh (sonic hedgehog) can reproduce this - its the morphogen
33
Q

what are the three places where the injection of wants or nodal can induce secondary axis?

A
  • injection of mRNA into dorsal marginal zone
  • Wnt8 (complete axis)
  • nodal (partial axis)
34
Q

notochord morphogen signalling for neurlation and somite development
(not a question, just a statement and look on the other side)

A

theres another axis- left and right
nodal and lefty are the two genes that show unequal expression between the left side of the embryo and the right side
when left and right get mixed up, situs invertus, body organs can be swapped over

35
Q

what do morphogen receptors signal?

A

they signal to the nucleus to initiate the appropriate differentiation programmes

36
Q

what are homeotic genes?

A
  • drosophila mutants were discovered with bits of bodies mixed up.
  • the mutation, that causes the transformation of an area to get mixed up with another area of the body. - the genes are called HOX genes (homeobox genes is the long way of saying it)
37
Q

what information is there about drosophila HOX genes?

A
  • each gene specifies the function of a segment
  • the HOX genes are arranged on the chromosome in a co-linear fashion
  • the mutations must be down to shuffling the gene order or duplication of specific
38
Q

what is an overview of what develops in ech stage of a pregnancy?

A

1st trimester- early cell divisions, the establishment of germ layers, the beginning of organogenesis
2nd trimester- organogenesis is completed
3rd trimester- fetal growth, organ systems become functional

39
Q

what happens in the determination of sex [humans]?

A

females- XX
males- XY
in females the gametes always have the X chromosome
in males, gametes either have an X or a Y chromosome, the chromosomes passed on from paternal side ‘determine’ the sex of the offspring
SYR is a gene which determines male characteristics on the Y chromosome
SYR codes for a ‘transcription factor’ which regulates many other genes

40
Q

what does SYR do overall?

A
  • it promotes the development of male reproductive anatomy

- it also suppresses the development of the female reproductive anatomy

41
Q

what information do you know on the clownflsh determination of sex?

A

in clownfish populations, there is 1 female and the rest are male
when the female dies, the dominant male changes to become the lone female

42
Q

what happens in the absense of the SYR gene?

A

female gonads develop, as they are the default

43
Q

what examples of sex chromosome abnormalities are there?

A

turners syndrome

Klinefelter’s syndrome

44
Q

what are the symptoms of turner’s syndrome?

A
  • females dont mature sexually
  • short stature, often other congenital abnormalities e.g. web of skin on either side of the neck
  • XO chromosomes
45
Q

what are the symptoms of kleinfelters syndrome?

A
  • male, sterile, testes are small and they may have breast growth
  • tend to be tall
  • they may have mental impairment

BM108 🧬 (17 decks)

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