Chapter 17- Sex Determination

1
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 _________
T4
In frogs- hormones __________ (T4) and
_________________ (T3) are secreted from the
________
T3
Fig. 18.3
2
A. Metamorphosis (cont.)
becomes giant _______

• If remove thyroid from tadpole-

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
_________
_______
___
_______
_______
3
A. Metamorphosis (cont.)
A. Metamorphosis (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
4
A. Metamorphosis (cont.)
A. Metamorphosis (cont.)
Fig. 18.7
Mechanism of thyroid hormone effects
Early metamorphosis
Metamorphosis
Pre-metamorphosis
____ T3r
_____ T3
____T3r
____ T3
T3 receptor gene
Activate ____________ genes
____T3,T4
______ T3,T4
_____ T3,T4
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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 _____________developmen
t
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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
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Heterochrony
1. ______________ (Salamander)
TSH-RF
T3, T4
TSH
No _______
No _________
No ________
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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 cant secrete ________________ _____
______ at low temps.
c. Other salamanders cant respond at all to
thyroid hormones
2. _________________ (Salamander)
a. Occidentalis (tree living salamander)
Remains in juvenile phase to retain _____________.
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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)
10
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

11
Recall Fruit Fly development
Fig. 18.12
Imaginal discs

• Imaginal discs lay dormant until needed to
  create adult

12
What dictates insect morphogenesis??
Answer Primarily ________(actually
20-hydroxyecdysone)
But, ___________ (JH) levels dictate __________
effect
Low Ecdysone
Next _______ stage
High ___
_______ stage
High Ecdysone
_______ stage
Low ___
High Ecdysone
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How does ecdysone work?

• Ecdysone cannot bind _____
• Must first bind the ecdysone _________

Fig. 18.23
The _______________ ______ binds DNA and creates
__________
These puffs contain _________ that are _________
These genes encode _____________________ that
promote _____________
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B. Regeneration
Three types-
1. ________ e.g. a salamander growing back an
entire limb
2. ____________ the re-patterning 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 ___________________
15
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)

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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 40longer) 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
Life span
3. _________________ genome damage
Leads to decreased ______ __________, increased
ROS, and increased ____________
DNA repair efficiency
Fig. 18.36
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B. Aging (cont.)
Theories of Aging
4. ___________ shortening
Background- Telomere ends are normally maintained
by the enzyme _____________ (not DNA polymerase)
Evidence-
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
18
B. Aging (cont.)
Fig. 18.37- 8 yr old children with progeria
Theories of Aging
5. __________ aging programs
Evidence-
a) Known old-age genetic defects

• Hutchinson-Gilford _______ syndrome in humans
  1/yr identified in US
• Disease gene identified- Nature, April 24,
  2003Gordon 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