Transcript Unit 7: Animal Reproduction and Development

Unit 7: Animal Reproduction and
Development
Chapter 39
Multiples
• Multiple births are becoming more common
– Incidence increased almost _________ in the past
two decades
– Fertility drugs and assisted reproduction
technologies are partly responsible
• Multiple births concern doctors
– Greater risk of :
– Multiple newborns usually have lower birth
weights and higher mortality rates
Modes of Reproduction
1. Sexual reproduction
– Meiosis (gamete formation) followed
by fertilization
– Offspring ______________________
2. Asexual reproduction
– Mitosis
– Single parent produces offspring
– Offspring are ____________________
Asexual Reproduction
• Budding (example: ____________)
• Fission (example: _____________)
• Useful strategy in stable environments
• All offspring are clones
Cost of Sexual Reproduction
• Specialized cells and structures must be
formed (to deliver/receive sperm)
– Reproductive timing; pheromones
• Visual signals, special courtship, and parental
behaviors can be costly
• Nurturing developing offspring, either in egg
or body, requires resources from mother
Costs of Sexual Reproduction
Costs of Sexual Reproduction
• Energy used to nourish offspring
– _______________: thick fluid containing
proteins and lipids to nourish the embryo until it
can feed
– Eggs with little yolk must develop larval stages
quickly
– Others have adequate food reserves for a more
lengthy development within the shell
– Some eggs have no yolk; energy must come
from ______________
Developmental Processes
Cell Growth
Cell differentiation
Morphogenesis
Stages of Development
Gamete formation
Fertilization
Cleavage (resulting blastula)
Gastrulation
Organ formation
Growth, tissue specialization
Each stage _________________________
Development Overview
Eggs form and mature in female
reproductive organs, and sperm
form and mature in male
reproductive organs.
Gamete formation
A sperm and an egg fuse at their
plasma membrane, then the nucleus
of one fuses with the nucleus of the
other to form the zygote.
Fertilization
By a series of mitotic cell divisions,
different daughter cells receive
different regions of the egg
cytoplasm.
Cleavage
Cell divisions, migrations, and
rearrangements produce two or
three primary tissues, the
forerunners of specialized tissues
and organs.
frog egg
frog sperm
Gastrulation
midsectional views
Subpopulations of cells are
sculpted into specialized organs
and tissues in prescribed spatial
patterns at prescribed times.
Organ formation
top view
Organs increase in size and
gradually assume specialized
functions.
Growth, tissue
specialization
side view
Fig.
39.4,
p.654
1. Gamete Formation
Sex Differences: Gamete Formation
Male
Female
____ sperm formed
Sperm much small
Human males produce
sperm throughout life
Meiosis completed during
spermatogenesis
____ egg formed
Egg larger: Why?
Human females have all
their eggs at birth
Meiosis completed after
fertilization
2. Fertilization
• Sperm fuses with ovum (egg)
• Complete when sperm nucleus fuses with egg
nucleus
• Internal (i.e. humans, primates, dragonflies; land
animals)
• External (i.e. fish, frogs, primarily aquatic)
• What are the advantages to internal vs. external
fertilization?
3. Cleavage
• Cell division (mitosis) during early development
• Increase in ____________, but not volume
Fig. 39.5b, p.655
Cleavage Patterns Vary
• Complete or incomplete (division limited to 1
part of egg)
• Examples of types of cleavage:
Radial cleavage:
_______________
Rotational cleavage:
_______________
3. Cleavage
• Cleavage results in blastomeres (each new cell)
• Each species has a characteristic cleavage pattern
Pattern dictates
what types and
proportions of
materials a
blastomere will get,
as well as its size
•
Fig. 39.5c, p.655
Frog Reproduction
adult,
three years
old
transformation to
adult nearly
completed
sexual reproduction
(meiosis through
fertilization)
cleavage
zygote
organ
formation tadpole
Fig.
39.5a,
p.655
Maternal Instructions
• Sperm contributes little more than the paternal DNA
• The egg cytoplasm contains enzymes, RNA
transcripts, microtubules, etc.
• These materials are not ______________
throughout the egg
– ________________________: certain materials
are located in a particular region
• The egg also contains yolk, which will influence
cleavage patterns
Cortex of Frog Egg
pigmented
cortex
gray
crescent
sperm
penetrating frog
egg
yolk-rich
cytoplasm
Fig. 39.6a, p.656
Experimental Evidence of
Localized Differences
Blastomeres
separated after
normal
cleavage
Fig. 39.6b, p.656
Blastomeres
separated so
one cell gets all
of gray
crescent
Maternal Instructions
• Penetration of egg by sperm triggers a structural
reorganization in the egg cytoplasm
• Frog egg: microtubules move granules from the
animal pole to form a ____________________
• Experiment done by Spemann demonstrates
importance of gray crescent
• Near the crescent, the body axis of the frog
embryo will become established and gastrulation
will begin
4. Morula
• Produced by embryonic cleavage
• Rapid cell division of the zygote with virtually no
growth
• Includes 16-cell, 32-cell, and 64-cell phases
• Solid ball
• After the 64-cell phase, develops into hollow ball,
the blastula.
5. Blastula
• Spherical layer of cells
(called ____________)
• Surrounding a fluid
filled cavity (called
____________)
6. Gastrulation
• Structural reorganization
• Some cells move inward
• Produces a
_____________ embryo
• Beginning of
differentiation:
____________________
____________________
Gastrula
3 germ layers formed:
• Endoderm
• Mesoderm
• Ectoderm
Late Gastrula
Endoderm
Ectoderm
Mesoderm
Gastrulation
• Results in three ________ layers, or tissues:
• Ectoderm: _____________
– Gives rise to the nervous system and the outer
layers of the integument
• Endoderm: _____________
– Gives rise to the gut and organs derived from it
• Mesoderm: ______________
– Muscle organs of circulation, reproduction,
excretion, and skeleton are derived from it