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Genetics > Lecture 10 > Flashcards

Lecture 10 Flashcards

1
Q

clone

A

genetically identical copy of an organism

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2
Q

cloning

A

procedures to create exact replica of a cell, tissue or organism

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3
Q

Natural clone

A

identical twins

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4
Q

why genetically clone?

A
  • improved productivity/welfare
    -disease resistance
  • reduce environmental footprint
  • preserve endangered wild species
  • animals as bioreactors - biomedicine/organs
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5
Q

what is a blastomere

A

cells formed through early division of a zygote

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6
Q

how do blastomeres form

A

through cleavage divisions

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7
Q

blastomeres are formed at what stage

A

2 -4cell stage

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8
Q

what can each blastomere develop into

A

an individual organism; one cell type

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9
Q

how many cell types are present at the blastocyst stage

A

2 cell types

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10
Q

describe the process of embryo twinning

A
  • single cell zygote has undergone first cell division
  • then the two zygotes are separated
  • embryo is transferred to an unrelated surrogate mother
  • sheep can give birth to identical twins
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11
Q

what are the pros and cons of embryo twinning

A

it mimics natural process but only limited number of clones can be produced

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12
Q

who is dolly the sheep

A

cloned sheep produced by somatic cell nuclear transfer

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13
Q

describe the process of SCNT

A

1a. remove nucleus of oocyte from cytoplasmic donor (enucleation)
1b. obtain donor nucleus from nucleus donor
2. introduce donor nucleus into enucleated oocyte
(nucleus of oocyte is replaced by nucleus of somatic cell)
(DNA of somatic cell is reprogrammed to pluripotent stem cell state)
3. transfer blastocyst to surrogate
(blastocyst develops into fetus in surrogate and a clone of the nucleus donor is born)

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14
Q

describe the general timeline of animal cloning (earliest to latest)

A
  1. sheep: embryo splitting
  2. cattle: embryo splitting
  3. sheep: embryo cloning
  4. cattle: embryo cloning
  5. sheep fetal and adult SCNT
  6. cattle: fetal and adult SCNT
  7. goat, pig
    8.cat
  8. horse
  9. dog
  10. camel
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15
Q

how can you clone for conservation

A

interspecies somatic nuclear cell transfer

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16
Q

what is an ex. of interpecies somatic nuclear transfer being used

A

domestic dog oocytes being used to clone coyotes - hybrid embryo

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17
Q

what are some potential problems of interspecies somatic nuclear cell transfer

A
  • nuclear DNA of cloned species, mitochondrial DNA from surrogate mother express genes necessary for energy production –> if there is no fit, developmental problems
  • embryo tissue/ placenta is recognized as foreign by immune system of surrogate mother
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18
Q

define reprogramming

A

the process of resetting adult nuclear DNA to the early development/pluripotent pattern of gene expression
(aka bringing differentiated somatic cell back to stem cell state)

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19
Q

why do problems sometimes occur during SCNT

A

Reprogramming is problematic!

  • switching on and off gene expression: errors in reprogramming may lead to abnormalities in gene expression in cloned animals and affect the health and longevity of the animal
  • epigenetic changes:, DNA methylation, histone modifications, imprinting, X-chromosome inactivation, chromatin remodelling
    …. can lead to: pregnancy losss, congenital abnormalities and postnatal mortality
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20
Q

what is cloning

A

generating genetically identical copies of cells, tissues and organisms

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21
Q

what is embryo twinning

A

microsurgical dissection of blastomeres at an early embryonal stage (2-4 cell stage); each blastomere can develop into an individual animal in surrogate mother
(aka. separate blastomeres –> each blastomere develops into a separate blastocyst)

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22
Q

describe somatic cell nuclear transfer

A

nucleus of donor cell is introduced into enucleated oocyst, then embryo transfer to surrogate

23
Q

where can the donor nuclei be obtained from for SCNT

A

donor nuclei can be obtained from fully differentiated cells (ex. fibroblasts)

24
Q

which SCNT nuclei is more efficient when…

A

nuclei from early embryonic stages

25
Q

SCNT was first shown in…

A

sheep

26
Q

which part of SCNT is problematic

A

reprogramming- the reset to pluripotent state of DNA

27
Q

what are GMOs/ transgenic animals

A

organisms whose genome has been altered using genetic engineering methods

28
Q

how are GMOs done

A

through deleting genes, introducing new genes and replacing gene order

29
Q

what are some goals of transgenic animals/ GMOs

A
  • improve/ enrich animal products
  • generate disease models
  • animals as bioreactors - production of recombinant relevant proteins (ex . spider goats)
30
Q

what opened the door for efficient creation of large transgenic animal species

A

SCNT

31
Q

what is a transgene

A

recombinant DNA introduced into an organism, transgene can then be introduced into cultured cells –> becomes the nuclei of selected transgenic cells and used for SCNT

32
Q

what are the steps for using SCNT for creating transgenic large animals

A

1a. create the transgenic cell: transfect somatic cells with transgene
1b. get oocyte and remove chromosomes for ennucleated oocyte to insert transgenic nuclei)
2. perform SCNT with nuclei of transgenic cells: ( first transgenic cells grow in vitro culture in selection, then expanded cells get transferred into ooplasm
3. embryo is transferred into recipient animal and then there is delivery of cloned calf (transgenic animal)

33
Q

what are the pros of transgenics

A
  • somatic cells can be cultured and manipulated ex vivo by introducing transgenes
  • transgenes/ recombo. DNA is incorporated into genome of cultured somatic cells
  • nuclei of manipulated somatic cells for SCNT
34
Q

what are the downsides of using transgenes*

A
  • transgene integrates randomly into genome - no control where and how many copies
  • could have integration of transgene into sliced gene regions –> no expression of transgene
  • expression to high if multiple copies are integrated –> high number of transgenes may be toxic
35
Q

genome/ gene editing

A

the ability to make changes at a specific site in the genome of an organism (deletion, replacement, editing/correcting DNA sequences)

36
Q

what is needed to achieve genome/ gene editing

A
  • nuclease: introduce double strand breaks into DNA
  • mechanism/component to direct the nuclease to the specific location in the genome
  • cellular DNA repair mechanisms that are activated in response to DS DNA breaks
37
Q

DNA double strand breaks (DSB) are what form of DNA damage

A

the most serious kind!

38
Q

how are dDSBs formed

A

through endogenous processes (ex. DNA replication) or exogenous agents (UV radiation, certain chemicals)wha

39
Q

what happens when there is failure to repair DSBs

A

cell death

40
Q

what are 2 mechanisms to repair DSBs

A
  • non homologous end joining
  • homology directed recombination
41
Q

how does Non-homologous end joining work

A
  • proteins recognize the breakage (direct recognition)
  • polymerase and lygase recognize and join DNA (processing)
  • 2 ends are joined together`
42
Q

what are the downsides of NHEJ

A

process is highly error prone
- can introduce indels into DNA
- frameshift/gene knockout

43
Q

What is homology directed recombination (HDR) used for

A
  • used to insert, delete or replace DNA sequences
44
Q

describe the repair template in HDR

A

linear DNA, homologous regions flanking the target DNA

45
Q

name 4 genome/gene editing tools on a scale from least to most feasible

A

meganucleases, zinc finger nucleases, TALEN, CRISPR/Cas9

46
Q

what are the most common genome/gene editing tools

A

Zinc finger nucleases, TALEN, now CRISPR/Cas9

47
Q

what is the nuclease used in zinc finger nucleases

A

FokI

48
Q

what is the DNA recognition component for ZFN

A

zinc finger motif (protein)

49
Q

describe zinc finger motifs

A

consist of 30 aa, recognizes triplet (3 nucleotides)

50
Q

typically, how many nucleotides are targetted and how many motifs are used to guide FokI to specific location

A

typically 9-18 NTs are targeted (3-6 motifs)

51
Q

what is the role of Zinc finger motifs

A

recognize sequence and where to put the DS DNA

52
Q

what are the cons of ZFNs

A

inflexible: relies on what motifs are available
- want to avoid off target effects

53
Q

what does TALEN stand for

A

transcription activator-like effector nucleases

Genetics (10 decks)

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