Animal Reproduction Chapter 48 Advanced Biology
48.1 ASEXUAL REPRODUCTION
Asexual reproduction – Result of mitosis and offspring are genetically identical.
 Identical copy of an organism is a clone.
 Three mechanisms of asexual reproduction.
1. Budding – When offspring starts being produced within or on a parent organism.
When new organism is developed enough it will be released from parent
organism
2. Fission – When parent organism divides and produces new organisms.
3. Parthenogenesis – When an unfertilized egg in the female doubles its chromosome
and then start developing or when mitosis produces and egg that start to
develop like regular zygote cell.
Sexual reproduction – Result of meiosis and fusion of gametes.
 Produces offspring that are genetically different form parents.
Gametogenesis – Process of forming gametes.
 Occurs in the organ called the gonad. Female gonad is the ovary and the male
gonad is the testes.
Spermatogenesis – Formation of sperm cells.
 Primary spermatocyte produces two spermatocytes and they in turn produce 4
spermatids.
 Each spermatid is 1n.
 Spermatogenesis occurs through the entire life span or the male.
Oogenesis – Formation of egg cells.
 Primary oocyte produces one secondary oocyte and one polar body. The
second oocyte produces one ootid and a polar body.
 Oogenesis allows one cell to gain almost all of the cytoplasm during meiosis I
and II leaving the other cell (polar body) with very little cytoplasm.
 The ootid will eventually produce a mature egg cell or ovum which will be used
in sexual reproduction.
 Ovum is 1n.
 In many mammals oogenesis stops with the primary oocytes undergoing
prophase I. This occurs before birth.
48.2 FERTILIZATION AND EGG DEVELOPMENT
Zygote – Cell formed from the union of egg and sperm.
Fertilization – Process of combining the male and female gametes.
External fertilization – When gametes meet on the outside of the organisms that produced
them.
 Most external fertilization occurs in water environments where the gametes can move
and become desiccated.
 Gametes are produced in larger amounts due to environmental biotic and abiotic
losses.
 External fertilization is controlled by external environment conditions, pheromones,
and behavior of organisms.
Internal fertilization – When gametes meet on the inside of the one the organisms that
produced them.
 Male reproductive structures are designed to place the sperm directly into the female
reproductive tract.
 Males can produce spermatophore; which holds all the sperm and that structure is
then placed into the female.
 Often sperm will compete with each other to fertilize eggs. Sperm competition is also
occurs between separate mating events with different males.
Adaptations of Internal fertilization:
 Some female species can choose specific sperm to fertilize the egg.
Femme Fatales - When females kill mates on during or after reproductive
events
 Giant sperm which inhibit second internal fertilization by another male.
 False reproductive structures
 Several mating events between mate and non-mates.
 Species that have both male and female gonads will fertilize eachother during the
mating events.
Egg Bearing or Live Bearing:
Oviparous – When the embryo develops in the external environment with covering that
protects it.
 Some species bear eggs and then leave them providing no care, while other
species provide intense care of the eggs they bear.
 Eggs contain all the needed nutrients needed to develop into juveniles.
Ovoviviparity – When the embryo develops in the internal environment with the
embryo providing all nutrients needed by the yolk stored in the egg.
Viviparous – When the embryo develops in the internal environment of the mother and
the embryo gets it nutrients from the mother.
48.3 REPRODUCTIVE STRUCTURES AND THEIR FUNCTIONS
MAMMAL MALE REPRODUCTIVE STRUCTURES
Scrotum – Sac like structure that holds the testes which produce sperm.
Epididymis – Structure that stores the sperm produced in the testes.
Semen – Fluid produced in the seminal vesicles, prostate gland, and bulbourethral gland that
will eventually carry sperm through the reproductive tract.
 Pathway of sperm through the male reproductive tract
TestesEpididymisVas DeferensEjaculatory ductUrethra
FEMALE REPRODUCTIVE STRUCTURES
Ovary – Structure that produces that eggs t.
Ovulation – Process by which the egg is released from the ovary.
Oviduct – Passageway the egg enters into from the ovary where it will become fertilized if
sperm are present and then will pass to the uterus.
 Pathway of egg through the female reproductive tract
OvaryOviductUterus
Uterus – Site where embryonic development takes place with regards to viviparous
development.d
Cervix – Opening of the uterus which will allow the fetus to leave the reproductive tract.
48.4 ROLE OF SEX HORMONES IN MAMMALIAN REPRODUCTION
Testosterone – Regulates development and maintenance of secondary sex characteristics in
males.
Estradiol – (Estrogen) Female sex hormone that regulates development and maintenance of
secondary sex characteristics.
 The hormones above affect development of reproductive tract in embryo, puberty
changes, and gametogenesis.
 Regulation of the sex homomes is done by the GnRH in the hypothalamus located at the
base of the brain.
 GnRH then cuases the release of LH Lueteinizing hormone and FSH Follicle stimulating
hormone.
 Both Lh and FSH are critical for ovulation.
Progesterone – Female sex hormone that prepares the uterus for pregnancy.
Menstrual cycle – Cycle that occurs in humans and some other primates which is on average
about a month long and is continuous throughout life or period of time.
 Preparation for ovulation of the secondary oocyte, fertilization, and implantation of egg
in the uterine lining.
 Divided generally into two phases that are on either side of the ovulation event.
Menstration – The shedding of the uterine lining in humans and some primates.
1. Follicular phase – Allows the oocyte to complete meiosis I and produce follicle cells
which will prepare it for ovulation.
 Estradiol is most active during this phase with a peak of LH and FSH hormones
right before ovulation.
Ovulation – The release of the secondary oocyte into the fallopian tube.
2. Luteal phase – When the follicle cells not connected with the secondary oocyte
degenerate.
 Progesterone is most common hormone during this phase with the other
hormones LH, FSH, and Estradiol decreasing after their peaks in the previous
to ovulation.
Estrous – Cycle which occurs is most animals and is generally occurs during a specific time of
the year.
 It is the cycle of preparation for ovulation of the secondary oocyte, fertilization, and
implantation of egg in the uterine lining.
 Most mammals do not shed the uterine lining but absorb it back into the uterus.
 Time when female mammals not including humans are sexually receptive is called estrus.
48.5 PREGNANCY AND BIRTH IN MAMMALS
Gestation – Time that the development takes place in the mother.
 Gestation can be 13 days for the opossum as a marsupial, 19 for eutherian domestic white
mouse.
 African Elephant has the longest gestation at 660 days.
Monotremes – Lay eggs and incubate them until hatching.
Marsupials – Corpus luteum is not maintained and placenta is not formed. Short gestation.
 Young develop quickly enough so that the jaws, lungs, guts, and forelimbs are developed
enough to that young developing marsupial can leave the reproductive tract be the end
of estrous and get to the pouch to complete development.
Eutherians – Nourish offspring for long periods supplying nourishment through the placenta.
Long gestation occurs in the eutherians.
Pregnancy – Time in from which the zygote develops and implants through the process of birth.
Embryo – Formed when the zygote starts to divide by mitosis.
 Mitosis starts occurring as soon as the egg has completed meiosis II and the both the eggs
and sperms DNA has fused to form a 2n number of chromosomes.
 Embryonic stage continues till all the basic main organs and external body structures are
produced.
 In humans this occurs in the 8th week
Fetus – The developing human after the 8th week which is growing and continuing developing
its body systems.
Implantation – The time when the embryo becomes embedded in the uterine lining.
 Embryo starts producing a hormone hCG (human chorionic gonadtropin) which prevents
the mothers menstral cycle from continuing.
 hCG is the chemical detected by pregnancy tests.
 Human pregnancy can be divided into three parts:
FIRST TRIMESTER: 0-12 weeks
 The cells of the embryo start to arrange themselves into three layers.
1. Ectoderm – Outer most layer that cells specialize to become the outer layer of the
skin and appendages the teeth, the lens of the eye, parts of the inner ear, the
nerves, brain, and spinal cord.
 Forms the amnion cells that produce a layer that surrounds the growing
embryo and amniotic fluid which provides a protective cushion.
2. Endoderm – Inner most layer cells that give rise to the respiratory and digestive
tracts it also produces the liver and pancreas.
3. Mesoderm – forms most the of the connective tissues of the body such as bone
and muscle.
 Placenta which is combination of tissues of the embryo and mother forms on the
uterine wall and supplies the nutrients and food needed for the new developing
human. The placenta will also carry waste materials away and transfer them to the
mother.
 The connection between mother and placenta is the umbilical cord.
 Placenta also releases hormones which do not allow ovulation to occur again.
 Pregnancy increases the womans blood volume by 50% and heart rate increases
cardiac output by 50%.
 Placenta also can transfer materials is should not like alcohol which causes Fetal
alcohol syndrome.
SECOND TRIMESTER: 13 – 28 Weeks
 Heart beat can be heard.
 Urine can be formed.
 Bone tissue start to form.
 Gonads start to develop as with the formation of other gender specific organs
 Facial features move to correct places and develop.
 Movements are coordinated from swallowing to other responsive movements.
 Hair and fingerprint form.
 Towards the end the baby can respond to stimulus including sound. Lungs are developing for
air.
 Can be about 9” and 2lbs.
 Viability (point at which a baby may survive being born) is during the 24th week. Every week
after increase the % chance of survival.
THIRD TRIMESTER: 29 – 40 weeks
 At start of third trimester babies have 90% survival rate after being born without any
impairments.
 Eyes can open and start detecting light
 Nervous system is completing development.
 Most of the growth occurs here.
Birthing Steps:
1.
2.
3.
4.
Cervix dilates or widens in response to hormone oxytocin
Uterine contractions increase in intensity, length, and frequency.
Baby is expelled by strong contractions through the cervix and vagina.
Babies umbilical cord is cut and following contractions then expel the rest of placenta
and membranes.