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Flashcards in BD17 Deck (28)
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1
Q

What is heterochrony

A

change in the rate, timing or sequence of development by either a mutation or during the course of evoltuion

2
Q

heterochrony and axolotls

A

A. mexicanum

look like larvae of other salamander species since they have gills etc and live in water.

3
Q

Paedomorphosis types

A

adult looks like a child

  1. neoteny: slower rate of development
  2. progenesis: end development early (axolotl)
  3. postdisplacement: start development alter but end at the same time
4
Q

peramorphosis types

A

child looks like an adult

  1. acceleration: faster rate of development
  2. hypermorphosis: end development is delayed
  3. predisplacment: development starts early but ends at the same time
5
Q

Paedomorphosis in salamanders

A

evolved atleast 6 times
- often said to be neoteny (slower rate of devel) but actually progenesis (end development early)
often evolved in caves

6
Q

clam paedomorphosis

A

C. fittoni adult clam looks like juvenille of ancestral C. pilcatum (but larger).
as cant observe development of fossil clams cant say what process caused this paedomorphosis

7
Q

dinosaur/bird paedomorphosis

A

dinos and bird skulls are paedomorphic:
crocs and primative dinos skulls flatten and elongate as they grow.
advanced dinos including birds and archaeopteryx retained the flat faced, large eyed features of birds.

8
Q

PCA

A

possibly correlated variables are converted to linearly uncorrelated variance (principle components).
the first principle component accound for as much of the variability in the data s possible
decreases with each componnent

9
Q

what does pca of dino skulls suggest

A

ontogenetic trajectories suggest that bird skulls are paedomorphic relatives to early dinos because of progenesis (end devel early)

10
Q

peramorphic trait birds

A

despite padeomorphism
the beak seems sto be peramorphic - an extended or accelerated growth of fronto nasal prominance relative to ancestor.
animal can simultaneosuly have both pedo/pero

11
Q

Cyprinid paedomorphosis

A
worlds smallest fish
sumatran cyprinid 
compared to zebrafish (relative) its missing late ossifying bones
seems to have minaturised by progenesis
however also have non-pedo features.
12
Q

peramorphosis in sharks

A

shark C. hastalis juvenile looks like adult of ancestral L. desori.
- cant observe devel of fossils dont know what waht causes this.

13
Q

peramorphosis irish elk

A

giant irish elk - megaloceros
extinct relative of moose had enormous antlers
possitive allometry = dissproportionate growth, larger body size, disproportionately larger the antlers.

14
Q

importance of thyroid hormone in amphibians

A

metamorphosis is controlled by thyroid hormone

15
Q

what are the biological actions of thryoid hromone mediated by
relevance in neoteny

A

NHRS: TRa and TRb

might be neoteny is due to a disabiling mutation in this pathway

thyroid injections can force tadpole metamoprhosis
axolotls go through metamoprhosis if give extra TH - potentially have a mutation in TH regulator.
mudpuppies dont go through metamorphosis if given thyroid hormone

16
Q

mudpuppies mutation

A

thought to be mutation in TRa/b a regulator or downstream genes

17
Q

salamander cross experiment

A

A. mexicanum cross with non-neotenic A. tigrum

QTL analysis shows single recessive allele at met-1 gene responsible for most of the difference.

appears to be controlling time of metamorphosis
-yet to be cloned.

18
Q

Heterochrony in salamander brain transcripome

A

tiger salamander and axolotl have 108 genes which are dynamic in expression in both species
some of these differ between species and are involved in hypothallamus piturity axis which may be important in regulating TH production.

19
Q

adult human skull

A

resemble juvenile great apes
weak jaws
larger brain case relative to jaw

20
Q

peado and peramorphosis in humans

A

paedomorphic in some respects but pera in others

- brains grow for longer and start earlier than ancestors

21
Q

sexual maturity paedomorphosis

A

neoteny
female chimps become sexually mature 8-9years
humans 13-14 years

22
Q

heterochrony in primate brain transcriptomes

experiment

A

analysed transcripts in dorsolateral prefrontal cortex of humans, chimps and rhesus monkeys over 0, 0.5, 2, 5, 10, 22 and 44 years

23
Q

heterochrony in primate brain transcriptome results

A

see human neoteny: pattern of expression is delayed in humans, looks like young ape conditon

  1. 299/7985 genes show rate heterochrony
  2. few shoe human acceleration (humans ahve greater expression)
  3. 38% show human neoteny - enriched for gray matter plasticity
    * * perhaps a marker of extended learning.
24
Q

synapse formation in humans

A

slower in pre-frontal cortex compared to chimps and macaques

- delayed more than would be predicted from rate of delay in sexual maturity.

25
Q

hypothesis for delay in synapse formation

A

synaptic plasticity is thought to be responsible for learning
once synpases are laid down, plasticity is lost.

26
Q

MEF2 genes

A

myocyte enhancement factor 2
show slower rate of increase (neoteny) in humans compared to chimps and macaques.
area around mef1 has a higher no. of human specific SNPs.
- suggest pos selection
- potentially responsible for delayed synpatogenesis.

27
Q

is autism heterochronic?

A

in childhood children develop a surplus of synapses in the pre-frontal cortex which get pruned back during adolescence and adulthood.

  • hypothesis is that pruning system is responsible for aduly traits - failure get juvenilisation
  • autism?
28
Q

infants and autists similarities

A
  1. prefers constant envrionments
  2. engage in repetitive behaviour - stimming
  3. rigid likes and dislikes
  4. high local and low global visual processing
  5. no theory of mind ; ability to internally model what other people are thinking - cant emphasize and strategise.