Sexual v. Asexual Reproduction
• Asexual advantage: reproduction when mates are scarce
• Asexual disadvantage: no recombination for variation
• Examples of asexual reproduction include:
! Fragmentation
! Fission
• Sexual animals may be:
! Facultative
! Obligatory
External v. Internal Fertilization
• Problem: How to get the sperm to the egg?
• External examples include:
! Acoelomates, Most molluscs, echinoderms
! Aquatic arthropods, fish, and amphibians
• Internal fertilization (copulation) necessary for terrestrial
• Internal fertilization occurs in:
! Some molluscs
! Segmented worms
! Insects & other terrestrial arthropods
! Reptiles, birds, and mammals
Mating Behavior
amplexus in frogs
“Birthing” Models
• Oviparous: external fertilization and development of
offspring occurs outside of the mother's body in many
egglayers.
• Ovoviviparous: fertilized eggs are retained within the
female and develop there but there is no apparent
connection between the embryo and the mother. The
egg hatches within the female and the young are born
alive (guppies).
• Viviparous: developing embryos are nourished within
the female. There is no eggshell or case around the
embryo (mammals).
Parthenogenesis
Daphnia magna
Parthenogenesis/Sexual Reproduction
(Dioecious)
Apis mellifera
Parthenogenesis/Sexual Reproduction
(Dioecious)
Parthenogenesis
Cnemidophorus tigris
Parthenogenesis
Hermaphrodism (Monoecious)
Marine Flatworm
Hermaphrodism (Monoecious)
Hermaphrodism (Sequential)
Thalassoma bifasciatum
Human Reproductive Anatomy (!)
Testes
Spermatogenesis
Anatomy of a Sperm Cell
Hormonal Control (!)
Human Reproductive Anatomy (")
Ovaries
Oogenesis
Anatomy of an Egg Cell (Ovum)
Hormonal Control (")
Spermatogenesis v. Oogenesis
• Spermatogenesis produces four haploid gametes from one
germ cell
• Oogenesis produces only one gamete from the original
germ cell (polar bodies degenerate)
• In spermatogenesis, the cytoplasm is divided evenly
among the daughter cells
• In oogenesis, the oocyte (egg) receives the majority of the
cytoplasm (significant later in maternal affect)
Spermatogenesis v. Oogenesis
• Spermatogenesis proceeds smoothly without pause
• Oogenesis halts twice:
! All ova are “frozen” at the primary oocyte stage at
birth, only to develop one-per-month starting at menses
! The 1st meiotic division occurs prior to ovulation
(recombination and reduction), but the second does not
occur until after fertilization!
Fertilization and Implantation
Fertilization and Implantation
Fertilization and Implantation
Fertilization and Implantation
Fertilization and Implantation
Fertilization and Implantation
Human Blastocyst (3-4 Days)
Human Embryo: 6 Weeks
Human Embryo: 7 Weeks
Brain has the first detectable brain waves, muscles develop and get stronger
Human Embryo: 8 Weeks
Eyes are well-developed, Fingers lengthen while distinct grooves (digital rays) form between the fingers.
Human Fetus: 11 Weeks
Period of rapid growth & development. Mother may first feel movements from weeks 9-11 .
Human Fetus: 12 Weeks
Fetus begins to move around, though the mother cannot yet sense these movements.
Human Fetus: 14 Weeks
Fetus is more flexible with ability to move head, mouth, lips, arms, wrists, hands, legs, feet, and toes.
Human Fetus: 16 Weeks
Human Fetus: 18 Weeks
Fetus has phases of sleep and waking and may prefer a favorite sleep position, temporary hair called
lanugo appears on the head.
Human Fetus: 20 Weeks
Fetus may suck on thumb. Extremely rapid brain growth; eyebrows and scalp hair become more visible
and fetus blinks more often.
Human Fetus: 24 Weeks
Fetal brain waves begin to activate auditory and visual systems, both mouth and lips show more
sensitivity. Eyes respond to light, while ears respond to sounds originating outside uterus.
Human Fetus: 32 Weeks
Eyes open during alert times and close during sleep. Eye color is usually blue, regardless of the
permanent color as pigmentation is not fully developed. Fingernails reach over finger tips and fetus can
scratch itself.
Placenta-Uterine Exchange
Hormonal Control of Labor
Human Birth (Parturition)
Cleavage
Gastrulation
Gastrulation
Organogenesis in Birds
Organogenesis
Formation of the Notochord
(Neuralization)
Fate Maps
Human Embryonic Development