Lecture 27 Animal Reproduction Flashcards
Animal reproduction
A population outlives its member only by reproduction, the generation of new
individuals from existing ones
Objectives for Reproduction
Differentiate reproduction strategies and advantages
Understand the importance of coordination for fertilization
Connect concepts across the module
Sexual reproduction
by fusion of haploid gametes, male
sperm and female eggs, to form a
diploid zygote
Asexual reproduction
without the fusion of egg and sperm
Hermaphroditism
An individual animal produces both male and female gametes
Any two individuals can mate under this system, and in some species, hermaphrodites can also self-fertilize
Mechanisms of Asexual reproduction
Fission, Fragmentation, Budding, Parthenogenesis
Fission
separation of a parent into two or more individuals of about the same size.
Fragmentation
breaking of the body into pieces, which develop into adults.
Budding
new individuals arise from outgrowths of existing ones
Parthenogenesis
is the development of a new individual from an unfertilized egg
The animal sexual life cycle
slide 10
The cost of sexual reproduction: sexual vs asexual
Sexual reproduction is the creation of an offspring by fusion of haploid gametes, male sperm and female eggs, to form a diploid zygote.
Sexual females have half as many daughters as asexual females; this is the “twofold cost” of sexual reproduction.
Despite this, almost all eukaryotic species reproduce sexually.
slide 11
The advantage of sexual reproduction
● Sexual reproduction may enhance reproductive success of parents when environmental factors change relatively rapidly.
● This is due to their production of genetically varied offspring.
● Asexual reproduction is expected to be most advantageous in stable, favorable environments.
Fertilization
The number of chromosomes in a haploid cell is 23. n=23. n=46
slide 15
Gametogenesis
the production of gametes
Spermatogenesis
the formation of sperm, is continuous and prolific.
● Hundreds of millions of sperm are produced per day; each sperm takes about 7 weeks to develop.
Oogenesis
the development of a mature egg, is a
prolonged process.
● Immature eggs form in the female embryo but do not complete their development until years or decades later.
Testes: Spermatogenesis
The male gonads, = testes, consist of highly coiled tubes surrounded by connective
tissue
seminiferous tubules
where sperm forms
Production of normal sperm cannot occur at the body temperatures of most mammals.
scrotum
where the testes of many mammals are held outside the abdominal cavity
temp is lower than in the abdominal cavity
Hormonal control of the testes
slide 19
Female ovary: Oogenesis
slide 20
Oogenesis starting at puberty
slide 21
Spermatogenesis versus oogenesis
Spermatogenesis differs from oogenesis in three ways:
● All four products of meiosis develop into sperm, while only one of the four becomes an egg.
● Spermatogenesis occurs throughout adolescence and adulthood.
● Sperm are produced continuously without the prolonged interruptions in oogenesis.
Fertilization
● Formation of a diploid (2n) zygote
from a haploid egg and sperm
● Depends on mechanisms that
bring together sperm and eggs of
the same species
● Two types
○ External fertilization
○ Internal fertilization
External fertilization
● Eggs shed by the female are fertilized by sperm in the external environment.
● A moist habitat is required
○ allow sperm to swim to the egg
○ to prevent the gametes from drying out.
Coordination
Timing is crucial to ensure that mature sperm and eggs encounter one another.
● Some species with external fertilization exhibit spawning, in which individuals cluster in the same area to release their gametes into the water at the same time.
● In some cases, chemical signals trigger spawning;
in others, environmental cues are responsible.
○ “courtship” behaviors leading to the fertilization of the
eggs of one female by one male
Internal fertilization
● An adaptation - enables sperm to reach an egg despite a dry external environment.
● Requirements
○ Behavioral interactions
○ Compatible copulatory organs.
● Mating animals may make use of pheromones, chemicals released by one organism that influence the physiology and behavior of individuals of the same species
Reproductive anatomy of the human female
slide 29
Fertilization and implantation
1.ovulation
2.fertilization
3.cleavage
4.cleavage continues
5.implantation
slide 30
what is the Acrosomal Reaction
the moment a sperm head contacts the egg
surface, molecules in the jelly coat trigger the
acrosomal reaction in the sperm.
● The Cortical Reaction
Model organism: Sea urchin fertilization
The acrosomal reaction ex
● Discharge of hydrolytic enzymes from the acrosome
● Digest the jelly coat, enabling a sperm structure called the acrosomal process to form, elongate, and penetrate the coat.
● Molecules and events at the egg surface play a crucial role in each step of fertilization:
○ Sperm penetrate the protective layer around the egg.
○ Receptors on the egg surface bind to molecules on
the sperm surface.
Polyspermy
the entry of multiple sperm nuclei into the egg
changes in the egg surface prevents this
The acrosomal and cortical reactions during sea urchin fertilization
slide 33
Cortical reactions
Sperm binding triggers a
cortical reaction,
● Depolarisation of
membrane - fast block
● the release of enzymes
from cortical granules to
the outside of the cell.
● catalyze changes in the
zona pellucida,
● slow block to
polyspermy. (No fast
block to polyspermy is
known in mammals.)
Fast block
immediately but temporarily blocks additional sperm from fertilizing the egg
Slow block
gradually establishes a permanent barrier to sperm entry
Changes in the uterus
define the menstrual cycle (also called the uterine cycle)
Changes in the ovaries
define the ovarian cycle
The reproductive cycles of the human female
part 1: FSH and LH levels
slide 37
Ovarian cycle and hormones
slide 38
When estradiol secretion by the follicle begins to rise steeply, FSH and LH levels increase markedly.
The maturing follicle enlarges to form a bulge at the surface of the ovary.
The follicular phase ends at ovulation, and the
secondary oocyte is released.
The luteal phase follows ovulation.
Uterine cycle and hormones
slide 40
Anterior pituitary hormones
slide 41, 42, 43
- The ovarian cycle begins when the hypothalamus releases GnRH.
- The GnRH stimulates the anterior pituitary to secrete small amounts of FSH and LH.
- FSH stimulates follicle growth, aided by LH
- The follicles start to make estradiol
The uterine cycle
Hormones coordinate the uterine cycle with
the ovarian cycle:
● Thickening of the endometrium during the
proliferative phase coordinates with the follicular phase.
● Secretion of nutrients during the secretory phase coordinates with the luteal phase.
● Shedding of the endometrium during the
menstrual flow phase coordinates with the growth of new ovarian follicles.
slide 45
Implantation: in the uterus
slide 46
the embryo implantation into the endometrium
Contraceptive methods
slide 47 and 48
In vitro fertilization (IVF)
slide 49 and 50
