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Genes Evo & Dev Y1 > GED L19 > Flashcards

GED L19 Flashcards

1
Q

Describe mosiaic development of Insect Embryos

A 
•	Mosaic Development -> Insect Embryos:
-	Pre-Fertilisation:
 Bicoid mRNA -> Anterior
                       Nanos mRNA -> Posterior
-	Fertilisation:
 Nuclear division -> Syncytium
 Development of Bicoid & Nanos proteins
-	Cellularisation:
 Acron-forming region
 Head-forming region 
 Thorax “
 Abdomen “
 Telson “
 Pole cells
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2
Q

Outline the pre-fertilisation stage of mosaic development in insect embryos

A
  • Pre-Fertilisation:
     Bicoid mRNA -> Anterior
     Nanos mRNA -> Posterior
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3
Q

Outline the fertilisation stage of mosaic development in insect embryos

A
  • Fertilisation:
     Nuclear division -> Syncytium
     Development of Bicoid & Nanos proteins
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4
Q

Outline the cellularisation stage of mosaic development in insect embryos

A 
-	Cellularisation:
 Acron-forming region
 Head-forming region 
 Thorax “
 Abdomen “
 Telson “
 Pole cells
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5
Q

Where is bicoid mRNA found in insect embryos during pre-fertilisation stage of mosaic development?

A

Anterior

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6
Q

Where is nanos mRNA found in insect embryos during pre-fertilisation stage of mosaic development?

A

Posterior

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7
Q

What type of mRNA is found in the anterior of insect embryos undergoing pre-fertilisation of mosaic development?

A

Bicoid

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8
Q

What type of mRNA is found in the posterior of insect embryos undergoing pre-fertilisation of mosaic development?

A

Nanos

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9
Q

Describe the main segments& their corresponding features present in a normal developed adult fruit fly

A
  • Normal Developed Adult:
     Notum & wings -> 2nd thoracic segment
     Halteres -> 3rd thoracic segment
    » Halteres -> Balance
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10
Q

What is found on the 2nd thoracic segment of adult fruit flies?

A

Notum & wings

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11
Q

What is found on the 3rd thoracic segment of adult fruit flies? What is the function of these?

A

Halteres -> Balance

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12
Q

Describe an example of a homeotic mutation in adult fruit flies

A
  • Homeotic Mutations:
     Examples
     Mutated bithorax complex:
     Transformation
    -> 3rd thoracic segment -> 2nd thoracic segment
    » 2nd segment replicated (3rd segment actually not present)
    > 2nd set of wings on duplicated segment (no haleteres)
     Mutation in antennapedia complex:
     Formation of legs instead of antennae
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13
Q

Describe the formation of a mutated bithorax complex in adult fruit flies

A

 Mutated bithorax complex:
 Transformation
-> 3rd thoracic segment -> 2nd thoracic segment
» 2nd segment replicated (3rd segment actually not present)
> 2nd set of wings on duplicated segment (no haleteres)

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14
Q

Describe the formation of a mutated antennapedia complex in adult fruit flies

A

 Mutation in antennapedia complex:

 Formation of legs instead of antennae

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15
Q

Describe the anterior / antennapedia genes responsible for homeotic mutations in flies

A

 Anterior > Antennapedia complex
 Head -> lab ; Dfd
 Thorax -> Scr ; Antp

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16
Q

Describe the posterior / bithorax complex genes responsible for homeotic mutations in flies

A

 Posterior > Bithorax complex

  Abdomen -> Ubx ; abdA ; AbdB

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17
Q

What is a homeotic mutation?

A

• Homeotic mutation:
- Transformation of one body part into another
» Development of correctly developed structure in incorrect location of body.
Eg. Legs instead of antennae -> Head
Wings instead of halteres. -> 2nd thoracic segment of insects.
- Hox genes location predicts location in which they will function
» Structural formation they cause
-> positioned along the body in corresponding location to where the gene is located
on chromosome.
Eg. Gene towards posterior end of chromosome codes for structural formations
towards posterior end of body.

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18
Q

Describe what a hox gene is

A

• Hox Genes:
- Cause homeotic transformations
 Formation of incorrect structure for specific region of body
&raquo_space; Expression of Hox gene (specific to one section of body) in the incorrect
corresponding location of body.
 Mutations preventing expression of Hox genes
&raquo_space; No formation of corresponding structure to that specific region of body.
- Hox genes location predicts location in which they will function
» Structural formation they cause
-> positioned along the body in corresponding location to where the gene is located
on chromosome.
Eg. Gene towards posterior end of chromosome codes for structural formations
towards posterior end of body.

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19
Q

Describe the characteristics of a hox gene

A
  • Evolutionarily conserved
  • All Hox genes have common ancestral gene
  • First identified -> Drosophila
  • Transcription factors
    » Bind with DNA
    > Control expression of other genes
  • Homeodomian
     60 aa helix-turn-helix DNA binding motif
  • Used to define anterior-posterior axis in organisms
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20
Q

Where are hox genes found?

A

 Present beside one another along same chromosome of genome.
 Each individual Hox gene only expressed in certain regions of body.
- Hox genes location predicts location in which they will function
» Structural formation they cause
-> positioned along the body in corresponding location to where the gene is located
on chromosome.
Eg. Gene towards posterior end of chromosome codes for structural formations
towards posterior end of body.

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21
Q

Describe the use of Gene Duplication Events

A
  • Gene Duplication Events
     Establishes gene redundancy
     Enables maintenance of some functions -> One of duplicated genes
    &raquo_space; Other can acquire new functions -> without loss of ancestral function.
    –» Development -> Novel function.
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22
Q

Outline the methods of gene duplication that occur

A

 Methods:
 Tandem Gene Duplication
 Segmental Duplication
 Whole Genome Duplication

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23
Q

What is tandem gene duplication & what does it involve?

A 
	Tandem Gene Duplication:
>> Creation of gene clusters 
 Unequal crossing-over 
>	Mis-pairing of chromosome during meiosis 
--> Possible cause -> Repeat DNA seq.
24
Q

What does tandem gene duplication result in?

A

Paralogous genes
Orthologous genes
Subfunctionalism

25
Q

What are paralogous genes?

A

 Paralogous genes:

 > Duplicated / same genes -> common ancestor -> within single chromosome

26
Q

What are analogous genes?

A

 Orthologous genes:

> Same gene present -> common ancestor -> diff. organisms

27
Q

Describe subfunctionalism

A

 Subfunctionalisation:
> Acquisition of new function -> duplicated gene
-> following multiple tandem gene duplications:
> Other function not lost -> multiple other duplicate genes still code for this function
-> No effect on organism.

28
Q

What are the methods of subfunctionalism?

A

> Methods:

  1. Duplication
  2. Divergence
29
Q

What happens if a new function is not acquired during subfunctionalism?

A

> Removal of duplicated gene if new function not acquired.

30
Q

Describe subfunctionalism by duplication

A
  1. Duplication
     Alteration -> Protein sequence
    -» Similar proteins & structures
    -» New binding properties / slightly diff. functions etc.
     Can also happen -> transcription factors
    Eg. Hox genes
    -» Same derived ancestral hox gene
    -> Different functions -> dependent on location of body in which expressed.
31
Q

Describe subfunctionalism by divergence

A

. Divergence
 Alteration -> Time / place of expression
-» Duplication -> Cis-regulatory elements
-» Mutations -> Regulatory regions
> New expression domains
> Change -> expression / timing
> Altered level of expression.

32
Q

Describe what whole genome duplication is

A

 Whole genome duplication:
 Duplication of single genome duplication event.
 Failure of meiosis -> Results in diploid germ cells (sperm/egg)
 Fertilisation -> tetraploid organism.

33
Q

Name the types of whole genome duplication

A
  1.  Allotetraploidy

2.  Autotetraploidy

34
Q

Describe allotetraploidy in whole genome duplication

A
  1.  Allotetraploidy
    &raquo_space; Hybridisation between 2 separate species
    –» Closely related enough for chromosomal cross-over
    –» Not sufficiently closely related for proper meiosis
    &raquo_space; Meiosis failure
    -» However 4 chromosomes not identical
    -> Not from same species.
35
Q

Describe autotetraploidy in whole genome duplication

A

 Autotetraploidy
&raquo_space; Duplication of genome through improper meiosis
&raquo_space; Meiosis failure
-» 4 identical chromosomes.

36
Q

Describe the formation of vertebrate lineages from whole genome duplication

A 
 Formation -> Vertebrate Lineage:
 2 rounds: (2R Hypothesis)
>> Duplication 
>> Gene Loss
>> 2nd Round Duplication
>> Gene Loss
 Results in Hox Genes
37
Q

Describe the order of vertebrate formation from whole genome duplication

A 
1st Event:
-> Lamprey Lineage (Jawless Fish) -> Most basal fish
2nd Event:
-> More advanced fishes
3rd Event:
 -> Bony Fish
38
Q

State the number of corresponding hox clusters possessed by the organisms formed during development of vertebrate lineages by whole genome duplication

A 
-> Lamprey Lineage (Jawless Fish) -> Most basal fish
    2 Hox Clusters
-> More advanced fishes
     4 Hox Clusters
 -> Bony Fish 
     8 Hox Clusters
39
Q

Describe the normal distribution of hox genes within organisms & how they occured

A 
•	Usually one hox cluster per organism
	All vertebrates have 4 hox clusters
 Formed -> Whole genome duplication
    >> 2 whole genome duplication events
          >  ancestral lineage leading -> vertebrates.
40
Q

What is allotetraploidy?

A

 Allotetraploidy

|&raquo_space; Hybridisation between 2 separate species

41
Q

What is autotetraploidy?

A

Autotetraploidy

|&raquo_space; Duplication of genome through improper meiosis

42
Q

Describe the result of tandem & segmental duplication by whole genome duplication in drosophila

A

 Tandem & segmental duplication
 2 hox clusters -> Drosophila
» ParaHox gene cluster
» Hox gene cluster

43
Q

Describe the distribution of Hox genes in humans

A 
•	Hox Genes: 
           39 Hox genes -> Humans
           4 clusters
              > 4 chromosomes
               >> Evolved -> set of 13 paralogous groups.
44
Q

What are hox genes thought to have developed from?

A

> > Evolved -> set of 13 paralogous groups.
 Related -> Fly homeotic genes
> Involved -> Anterior-posterior patterning

45
Q

Describe segmental duplication

A

 Segmental duplication:
 Similar -> Giant tandem duplication
&raquo_space; Affects whole sections of chromosome
 Elongation -> existing gene clusters
&raquo_space; (Formed -> Tandem gene duplication)
&raquo_space; Localised, duplicated genes already exist -> related to one another.
-> Uneven cross-over
> Further incr. number of duplicated genes in this region.

46
Q

Describe the characteristics of Hox genes

A

 Evolutionarily conserved
 Illustrate co-linearity
&raquo_space; HoxA1 paralogous -> HoxB1 etc.
 Order along chromosome
 Limit of location of Hox genes & expression within bodily sections.
 Expression changes relating to number of vertebra

47
Q

Describe the order of hox genes along the chromosome

A

 Order along chromosome
&raquo_space; Spatial temporal expression pattern -> anterior-posterior axis
—> HoxA3
&raquo_space; Found -> Anterior end of cluster & chromosome
&raquo_space; Expressed -> Anterior end of body
–> HoxA3 -> Anterior to HoxA5 -> Cluster & chromosome
-> Expression of HoxA3 -> Anterior to expression of HoxA5 -> body
–> HoxA5 location -> Cluster & expression -> Anterior to HoxA9
&raquo_space;( Loxation in cluster corresponds to location expressed in body
–>Anterior location on chromosome & cluster -> Anterior location on body
Location corresponds to number -> A3 anterior to A5
A5 anterior to A9
–>Applies for location on chromosome / cluster & corresponding body location for
expression. ))
 Limit of location of Hox genes & expression within bodily sections.
 Expression changes relating to number of vertebra
&raquo_space; Birds -> 14 cervical vertebra
&raquo_space; Humans -> 7
 Number depends -> Location -> Hox gene expression terminates.
&raquo_space; Chicks -> Boundary between HoxC5 & Hox6 Gene Domain
( -> Boundary between last cervical vertebra & first
thoracic vertebra )
-> After 14th somite
&raquo_space; Mammals -> After 7th somite.
Therefore:
–» Position of Hox Gene Expression determines number of associated vertebra possessed.
–» Strong correlation -> Hox gene expression & anatomical features.

48
Q

Describe the relationship between hox genes & vertebra

A

 Expression changes relating to number of vertebra
&raquo_space; Birds -> 14 cervical vertebra
&raquo_space; Humans -> 7
 Number depends -> Location -> Hox gene expression terminates.
&raquo_space; Chicks -> Boundary between HoxC5 & Hox6 Gene Domain
( -> Boundary between last cervical vertebra & first
thoracic vertebra )
-> After 14th somite
&raquo_space; Mammals -> After 7th somite.
Therefore:
–» Position of Hox Gene Expression determines number of associated vertebra possessed.
–» Strong correlation -> Hox gene expression & anatomical features.

49
Q

Describe single hox mutations & describe an example

A
  • Single Hox mutations are generally subtle
    &raquo_space; Redundancy -> Other Hox genes already have function of lost genes.
    Eg. Hoxc8 -> Mice
    &raquo_space; Normally involved -> Limitation boundary -> Thoracic & lumbar segments
     Mutant / elimination
    > Instead -> 1st lumbar vertebra
    » Becomes Thoracic vertebra -> Extra rib
50
Q

Describe Hox11 paralogue mutants

A
  • Hox11 paralogue mutants

 All sacral vertebrates transformed -> lumbar vertebrae

51
Q

Describe elimination of all paralogous genes by hox mutations & describe an example

A
  • Elimination -> All paralogous genes
    -> So redundancy doesn’t minimise effect of mutation
    Eg. Hox10 paralogue mutants
    &raquo_space; Eliminate Hox 10A, 10C & 10D
     All lumbar vertebrae transformed -> thoracic vertebrae
52
Q

What is the function of hox gene expression?

A

Hox gene expression

- Gives positional identity along anterior-posterios axis

53
Q

Give evidence for the relationship between positional identity on the anterior-posterior axis & hox gene expression.

A

Evidence:
 Expression pattern
 Comparative embryology
 Gene knockout experiments

54
Q

Describe the relationship between anterior-posterior patterning & hox gene

A
  • Anterior posterior patterning
     Hox genes expressed -> Distinct proximal-distal pattern
    » Hoxa paralogues
    » Hoxd paralogues
     Mutations -> paralogous Hox genes
    > Major disruptions -> limb skeletal morphology
55
Q

Describe the relationship between proximal-distal identities & hox gene association

A
  • Hox Genes control Proximal-Distal identities:
    Paralogue groups:
    » 9 -> Scapula
    » 10 -> Humerus
    » 11 -> Ulna & Digits
    » 12 -> Metacarpals
    » 13 -> Digits
     Synpolydactyl phenotype with HOXD13 mutation (+10 Ala expansion)
    > Fusion of digits in hands & feet
56
Q

What are the rules regarding Vertebrate Hox Genes?

A

• Rules -> Vertebrate Hox Genes:
- Generated through tandem & segmental duplication events
- Expressed -> spatial domains -> along AP
- Expression domains overlap
- Patterns -> Combinatorial code / Hox Code
- Vertebrate clusters arise
 2 Whole genome duplication events
> Leads -> partial redundancy
- Spatial colinearity
- Temporal collinearity
- Evidence -> homeotic functions (knock outs)
- Hox gene toolkit acquired novel function -> vertebrates
 Proximal-distal patterning of limb
- Common ancestor of flies & vertebrates
 Hox cluster -> Role in AP patterning

Genes Evo & Dev Y1 (23 decks)

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