BD17

Question 1

What is heterochrony

Answer 1

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

Question 2

heterochrony and axolotls

Answer 2

A. mexicanum

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

Question 3

Paedomorphosis types

Answer 3

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

Question 4

peramorphosis types

Answer 4

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

Question 5

Paedomorphosis in salamanders

Answer 5

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

Question 6

clam paedomorphosis

Answer 6

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

Question 7

dinosaur/bird paedomorphosis

Answer 7

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.

Question 8

PCA

Answer 8

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

Question 9

what does pca of dino skulls suggest

Answer 9

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

Question 10

peramorphic trait birds

Answer 10

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

Question 11

Cyprinid paedomorphosis

Answer 11

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.

Question 12

peramorphosis in sharks

Answer 12

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

Question 13

peramorphosis irish elk

Answer 13

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

Question 14

importance of thyroid hormone in amphibians

Answer 14

metamorphosis is controlled by thyroid hormone

Question 15

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

Answer 15

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

Question 16

mudpuppies mutation

Answer 16

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

Question 17

salamander cross experiment

Answer 17

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.

Question 18

Heterochrony in salamander brain transcripome

Answer 18

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.

Question 19

adult human skull

Answer 19

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

Question 20

peado and peramorphosis in humans

Answer 20

paedomorphic in some respects but pera in others

- brains grow for longer and start earlier than ancestors

Question 21

sexual maturity paedomorphosis

Answer 21

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

Question 22

heterochrony in primate brain transcriptomes

experiment

Answer 22

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

Question 23

heterochrony in primate brain transcriptome results

Answer 23

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.

Question 24

synapse formation in humans

Answer 24

slower in pre-frontal cortex compared to chimps and macaques

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

Question 25

hypothesis for delay in synapse formation

Answer 25

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

Question 26

MEF2 genes

Answer 26

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.

Question 27

is autism heterochronic?

Answer 27

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?

Question 28

infants and autists similarities

Answer 28

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.