Animal Reproduction
&
Development
AP Biology 2007-2008

Asexual Reproduction

Fission

Budding

Fragmentation

Regeneration
I always wanted to be JUST LIKE my parents…
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Reproductive Cycles

Parthenogenesis:

Process in which the egg develops without fertilization

Hermaphroditism:

Individual has both male and female reproductive systems

Sequential – individuals reverse their sex within a lifetime.
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Mechanisms of Sexual Repro:

External Fertilization (External
Development)

Eggs are shed, males fertilize

Requires moist habitat
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Mechanisms of Sexual Repro:

Internal Fertilization

Sperm is deposited into female

May be stored in seminal receptacle / spermatheca.

Pheromones – chemical signals released that influence behavior in another organism

May have external or internal development.
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Reproductive Systems:
Flatworm
(Platyhelminthes)
Hermaphroditic
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Reproductive Systems:

Insect:

Male:
 Testes  vas deferens
 seminal vesicles = storage

Female:
 Ovaries
 oviduct
 vagina = fertilization occurs here.
 Spermatheca
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Reproductive Systems

Male
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Reproductive Systems:

Female
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Oogenesis
What is the advantage of this development system?

Unequal meiotic divisions
 unequal distribution of cytoplasm

1 egg

2 polar bodies
Meiosis 1 completed during egg maturation
Meiosis 2 completed triggered by fertilization
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Put all your egg in one basket! ovulation

Hormonal Control: Male
GnRH
FSH LH
Testes:
Seminiferous tubules to produce sperm.
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Hormonal Control: Female
Hypothalamus
GnRH
Pituitary Gland
LH:
(Day 14 when estrogen peaks)
FSH
Stimulates ovulation
Corpus luteum :
Produces progesterone to maintain pregnancy.
Inhibits FSH & LH.
Ovaries:
Stimulates follicle to develop – follicle cells produce estrogen
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Follicle Development:
Progesterone
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Peak in LH!!

Females – Putting it all together!
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Fertilization – Development:
 fertilization
 cleavage
 gastrulation
 neurulation
 organogenesis
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In The Womb
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Fertilization (Acrosomal Reaction):

Joining of sperm & egg
 sperm head (nucleus) enters egg
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Cleavage

Repeated mitotic divisions of zygote

1st step to becoming multicellular
 unequal divisions establishes body plan
 different cells receive different portions of egg cytoplasm & therefore different regulatory signals
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Cleavage
 zygote
 morula
 blastula
 establishes future development zygote gastrulation blastula

Blastocyst (Human blastula)

@ 100 cells, day 7

Inner cell mass
 embryo proper

Tropholast
 fetal portion of placenta
(chorion & amnion form)

Implantation occurs – produce chorionic villi
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Gastrulation

Establish 3 cell layers
 ectoderm
 outer body tissues
 skin, nails, teeth
 nerves, eyes, lining of mouth gastrulation in primitive chordates ectoderm
 mesoderm
 middle tissues
 blood & lymph, bone & notochord, muscle
 excretory & reproductive systems
 endoderm
 inner lining
 digestive system
 lining of respiratory, excretory & reproductive systems endoderm mesoderm

Testing…
In a study of the development of frogs, groups of cells in the germ layers of several embryos in the early gastrula stage were stained with five different dyes that do not harm living tissue. After organogenesis (organ formation), the location of the dyes was noted, as shown in the table below.
Tissue
Brain
Notochord
Liver
Lens of the eye
Lining of the digestive tract
Stain
Red
Yellow
Green
Blue
Purple
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Neurulation

Formation of notochord & neural tube
 develop into nervous system
Neural tube develops into CNS
(brain & spinal cord)
Notochord develops into vertebral column
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Echinodermata

Holoblastic cleavage : complete division to form blastomeres

Deuterostomes : anus develops from blastopore.

Protostomes : mouth develops from blastopore.
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Body Plan
Animal pole : usually forms embryo
Vegetal pole :
Usually contains yolk
Amphibians:
Meroblastic cleavage
Grey crescent – first cleavage occurs here
Dorsal Lip – involution occurs here
Yolk plug forms at blastopore .
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Avian (Chick):

Blastodisc

Primitive Streak

Epiblast: gives rise to embryo

Hypoblast: gives rise to yolk sac.
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Avian Organogenesis:
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Organogenesis trophoblast,
Mammalian embryo
Umbilical blood vessels surround embryo
Chorion
Bird embryo
Amnion
Encloses embryo in amniotic fluid.
Yolk sac
Site of early
Allantois
Forms umbilical blood cell
Fetal blood vessels cord where blood
Placenta
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Maternal blood vessels

Placenta

Materials exchange across membranes
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Human fetal development
4 weeks 7 weeks
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Human fetal development
10 weeks
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Human fetal development
20 weeks

Human fetal development

The fetus just spends much of the 2 nd &
3 rd trimesters just growing
…and doing various flip-turns & kicks inside amniotic fluid
Week 20
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Human fetal development

24 weeks (6 months; 2nd trimester)
Fetus is covered with fine, downy hair called lanugo . Its skin is protected by a waxy material called vernix
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Human fetal development

30 weeks (7.5 months)
Umbilical cord
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Getting crowded in there!!

32 weeks (8 months)
The fetus sleeps 90-95% of the day & sometimes experiences
REM sleep, an indication of dreaming
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Birth

Birth (36 weeks)
Intestine
Placenta
Umbilical cord
Wall of uterus
Bladder
Cervix

The end of the journey!
And you think
9 months of
AP Bio is hard
!
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TED – Conception to Birth
Visualized
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Mechanisms of Development

Morphogenesis: development of body shape and organization that occurs


Cell shape – cytoskeleton changes shape i.e. neural tube formation
Cell movement – cells move laterally, change in cytoskeleton

Convergent extension - cells converge (sheets become narrower) and extend. i.e. archenteron

ECM plays a major role


CAMs – cell adhesion molecules
Cadherins – cell to cell adhesion molecules
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Mechanisms of Development

Cytoplasmic Determinants-

RNA, proteins, hormones, etc. will be produced at different concentrations turning different genes on in different cells as they divide.
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Cell Differetiation
 1920’s W. Vogt – Fate Maps

Body Axis – cytoplasmic determinants i.e Drosophila dorsal / ventral axes

Cellular Potency-

Totipotent – give rise to new embryo

Induction – one group induces another type of tissue to form.

Pattern formation – arrangement of organs in 3D space. i.e. limb bud
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Limb Bud Formation

AER – apical ectodermal ridge

Proximal / distal growth

Secretes FGF – fibroblast growth factor

ZPA – zone of polarizing activity

Anterior / posterior growth

Secretes morphogens – Sonic hedgehog (Homeobox or HOX gene)
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