Transcript Chapter 17- Sex Determination

Chapter 18- Metamorphosis/regeneration/aging
A. ___________________
Most animals have a distinct larval stage
Massive changes often occur from larval to adult organism transition
Adult
Larva
Aquatic, tail fins
Gills
Herbivore
Excrete ammonia
Terrestrial, tail-less, ________
_________
___________
Excrete __________
Metamorphosis is dictated by _________
In frogs- hormones __________
(T4) and _________________
(T3) are secreted from the
________
Fig. 18.3
T4
T3
A. Metamorphosis (cont.)
•If remove thyroid from tadpole-
…becomes giant _______
The response to hormones is ____________ specific
• The same stimulus can promote ___________in one tissue and
______________ in another
• T3 promotes ____________ of tadpole head and body, but
cell ___________ in the tail
The timing of hormone production is done by
1. The____________
2. The _________________ (which regulates thyroid
hormone production)
___
Thyroid stimulating
hormone
Hypothalamus
_________
_______
_______
_______
___
A. Metamorphosis
Metamorphosis (cont.)
(cont.)
•If transplant a second tail- it still degenerates by ________
Fig. 18.5
Transplanted
tail tip
Transplanted
tail tip regresses
•But if transplant another eye cup, it ________________
How are these events of metamorphosis coordinated??
•Need tail until have legs for locomotion
•Need gills until lung muscles develop
One theory- “______________________________”
•As _____________ levels increase, different events occur
•If high levels of ________________ -tail regression prior to
_________________ development
Go to morphogenesis on Vade Mecum
A. Metamorphosis
Metamorphosis (cont.)
(cont.)
Fig. 18.7
Mechanism of thyroid hormone effects
Early metamorphosis
Pre-metamorphosis
_____ T3
____ T3r
T3
T3r
Metamorphosis
____ T3
____T3r
T3 receptor gene
Activate ____________ genes
____T3,T4
______ T3,T4
_____ T3,T4
A. Metamorphosis (cont.)
Heterochrony
Definition- The phenomenon whereby animals change
the ______________ and ____________________ of
characters
Usually refers to creatures with _________ phases
1. __________- retention of juvenile form in body but germ
cells/gonads mature _______________
2.___________- retention of juvenile form of body but germ
cells and gonads mature ____________________________
3. ___________________
no _____________development
A. Metamorphosis (cont.)
1. ___________ (Salamander)
a. Mexican axolotl- body fails to mature do to lack of
__________ from pituitary gland (hence no ___ produced by
thyroid gland)
•If treat axolotl with __________________, develops
into creature not seen in nature
Normal
+ __________
Fig. 18.8
Heterochrony
1. ______________ (Salamander)
TSH-RF
No ________
TSH
No _______
T3, T4
No _________
A. Metamorphosis (cont.)
1. Neoteny (Salamander)
b. Tigrinum (salamander in Rocky Mtns) stays in larval
form if cold
Metamorph into land-dwelling creature if _____
Why? Because can’t secrete ________________
___________ at low temps.
c. Other salamanders can’t respond at all to thyroid hormones
2. _________________ (Salamander)
a. Occidentalis (tree living salamander)
Remains in juvenile phase to retain _____________.
A. Metamorphosis (cont.)
3. ___________ Development
E. Coqui (frog) – In _____________ only
Develops directly into frog (no ____________ stage)
• Egg is 20X larger than xenopus
• Early development is similar to other frogs , but
____________ form right after __________ closure
Fig. 18.10
Is larval stage only required for
creatures with small eggs??
1998- Noisy problem when introduced into Hawaii- cluster can produce 70-90 decibels
(75 decibels leads to hearing loss)
Insect morphogenesis
• Instead of simply remodeling (e.g.
amphibians), insects _______ tissues and
___________ new ones
Insects ______ (shed their cuticle)
• Often go through multiple _________ (larval molts)
• Each molt generates a ________ organism
• Most of the previous body is destroyed by _________
• _____________ lay dormant until needed to create adult
Recall Fruit Fly development
Imaginal discs
Fig. 18.12
• Imaginal discs lay dormant until needed to create adult
What dictates insect morphogenesis??
Answer: Primarily ________(actually 20-hydroxyecdysone)
But, ___________ (JH) levels dictate __________ effect
Next _______ stage
High ___
_______ stage
_______ stage
Low ___
High Ecdysone
How does ecdysone work?
• Ecdysone cannot bind _____
• Must first bind the ecdysone _________
The _______________
______ binds DNA and
creates “__________”
These puffs contain _________
that are _________
These genes encode
_____________________
that promote _____________
Fig. 18.23
B. Regeneration
Three types1. ________ – e.g. a salamander growing back an entire limb
2. ____________ – the repatterning of existing tissues,
without requiring ____________
e.g. planaria regeneration of
head and tail regions
3. _____________ – cells divide but maintain their
____________ phenotype
e.g. the mammalian ______- the removed lobe does not
grow back, but the remaining _____ compensate by
“___________________”
C. Aging
Definition- Time-related ______________of the physiological
functions necessary for survival and function
Some developmental biologists tout that animals are only needed
long enough to fill the need of ________________, then die (as
occurs in ______ and __________)
Maximum life span- the _______________ number of
years that a member of a species is known to have lived
Life ___________- the age to which __ of the population survives
•In 1780 England- ___ yrs
•In 1780 Massachusetts- ___ yrs
•Today in Afghanistan, Cambodia, etc- ____ yrs
•Today in America- ___ yrs (male) and __ yrs (female)
•In 1935 America- ____ yrs (when Social Security was initiated)
B. Aging (cont.)
Theories of Aging
1. _____________- reactive oxygen species (ROS) in
mitochondria progressively damage DNA, proteins, etc
Evidence- Drosophila and C. Elegans liver longer (up to
40%longer) if over-express catalase (which destroys ROS)
2. General ______________- the build up of__________________
Evidence- Species with more efficient
DNA repair enzymes tend to live longer
3. _________________ genome damage
Leads to decreased ______
__________, increased ROS, and
increased ____________
Fig. 18.36
B. Aging (cont.)
Theories of Aging
13.2
4. ___________ shortening
Background- Telomere ends are
normally maintained by the enzyme
_____________ (not DNA
polymerase)
Evidence-
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.3
a) Telomeres shorten as cells divide in culture until cell division
stops, and cell division starts again if express telomerase
b) Telomerase-deficient mice show profound ________ defects
Problem with theory- _________________ between telomere
length and life span of different species or even with a species
B. Aging (cont.)
Fig. 18.37- 8 yr old
children with
progeria
Theories of Aging
5. __________ aging programs
Evidencea) Known “old-age” genetic defects
1) Hutchinson-Gilford _______ syndrome
in humans – 1/yr identified in US
• Disease gene identified- Nature, April
24, 2003;Gordon et al.
•
•
Leslie Gordon is mother of progeria child
C to T transition in LMNA (Lamin
A) gene (unknown function)
2) __________ gene mutation in mice
b) C. elegans- can extend lives __________ by altering
genes involved in larva- to adult genetic pathway