BIOL10004 Lecture Notes - Parthenogenesis, Egg Cell, Gamete
14 Jun 2018
School
Department
Course
Professor
Semester 1, 2018 Sam Midler
BIOL – Lecture 19
Reproduction I
Asexual reproduction
• mitotic cell division
• offspring genetically identical to parents
o no exchange of genetic material
• allows a single individual to produce a colony
o corals, hydra (budding), sea stars (fragmentation)
• common among invertebrates but also some vertebrates
o stream fish, some geckos, snakes and sharks
parthenogenesis
• advantageous for animals living in constant, stable environments
• parthenogenesis occurs through use of ova and the female reproductive system
o process where an egg develops without being fertilised
• also occurs in fluctuating environments
• facultative parthenogenesis – use asexual or sexual reproduction depending on
environment, food resources and mate availability
sexual reproduction
• exchange of genetic information
• common strategy among both invertebrates and vertebrates
• needs two sexes – female / male
o female: produce a few large gametes (eggs) – non-motile, contribute all
cytoplasm and DNA → embryo
o male: produce many small gametes (Sperm) – motile, usually only contribute
DNA
mitosis and meiosis
• mitosis
o somatic cell division
o no exchange or genetic material
o asexual reproduction
• meiosis
o specialised form of cell division
o haploid (1n) gametes fuse to
form a new diploid (2n) individual
o sexual reproduction
• sexual reproduction requires
mechanisms to get sperm and egg
together → fertilisation
o offspring a combination of
genetics
find more resources at oneclass.com
find more resources at oneclass.com
Semester 1, 2018 Sam Midler
variations
• hermaphrodite
o same individual produces both sperm and eggs
o may be able to self-fertilise but common for sperm and eggs to be made at
different times
o may involve sex-change
• Protandry – animal that produces sperm when young and can transform to produce
eggs in later life stages
• Protogyny – animal that produces eggs when young and can transform to produce
sperm in later life stages
Gamete production and delivery
• To reproduce sexually, animals must have systems that produce gametes
(gametogenesis)
• The least complex systems do not contain distinct gonads, the organs that produce
gametes in most animals
• The most complex reproductive systems contain many sets of accessory tubes and
glands that carry, nourish and protect the gametes and developing embryos
Reproductive tracts: basic design
• Terminology:
o Gonads – testes and ovaries
o Gametes – sperm and eggs
o Ducts – regionally specialised for specific roles
o Genital – relating to reproductive system
Male
• Testis – sperm production, hormones
• Accessory organs (e.g. prostate)
o Bulk of semen
o Lubrication
o Assist fertilisation
• Ducts - convey sperm
o Maturation and storage
• Conveyed to external genitals → transfer
sperm
Female
• Ovary – egg production, hormones
• Ducts
o Convey eggs
o Add protective coats
o Sperm and fertilisation
o Maturation of embryo
• External genitals → transfer eggs
find more resources at oneclass.com
find more resources at oneclass.com
Semester 1, 2018 Sam Midler
External vs. internal fertilisation
• external
o eggs shed by female are fertilised by sperm in external environment
▪ e.g. fish, amphibians
o timing of release is crucial, often mediated by environmental cues,
pheromones and/or courtship behaviour
o usually large numbers of gametes
o aquatic environments
o e.g. toad – no specialised external genitals needed – males have nuptial pads
on forelimbs to grasp female in amplexus (position)
• internal
o requires important interactions often mediated by environmental cues,
pheromones and/or courtship behaviours
o requires specialisation on external genitalia compatible between the two
sexes to allow sperm transfer
▪ most species that do this possess some form of intromittent organ to
increase efficiency of sperm transfer → e.g. Spiders have a leg-like
appendage, sharks have claspers, true penis (direct extension)
o sperm are deposited in or near female tract, and fertilisation occurs within
o needs fewer gametes, but often very high number of sperm
o works in dry environments
o prerequisite to viviparity – internal gestation, birth of live young
other reproductive organs
• placenta
o nutrient transfer in species with internal development
o hormone production
• mammary glands – nutrient transfer in mammals
• brain
o reproductive behaviour
o hormone control
reproductive strategies: costs and benefits
characteristic
Benefit
Cost
Mating displays
Attracting mates
Attracting predators
Harems (polygynous)
Access to mates
Male fighting
External fertilisation
Physiology simple
High loss of gametes
Internal fertilisation
Make fewer eggs/sperm
Complex physiology
Viviparity
High survival of young
Risk to pregnant mother
Postnatal care
High survival of young
Huge investment of parents
find more resources at oneclass.com
find more resources at oneclass.com
Document Summary
Reproductive tracts: basic design: terminology, gonads testes and ovaries, gametes sperm and eggs, ducts regionally specialised for specific roles, genital relating to reproductive system. Male: testis sperm production, hormones, accessory organs (e. g. prostate, bulk of semen, lubrication, assist fertilisation, ducts - convey sperm, maturation and storage, conveyed to external genitals transfer sperm. Female: ovary egg production, hormones, ducts, convey eggs, add protective coats, sperm and fertilisation, maturation of embryo, external genitals transfer eggs. Structure and function: sperm production, occurs in seminiferous tubules, controlled by sertoli (nurse) cells, spermatogenesis, hormone production, testosterone steroid, androgen, made by leydig cells in between tubules spermatogenesis. Inhibin (from sertoli cells) inhibits fsdh secretion negative feedback: relatively constant t homeostatic control. Ovarian follicle and hormones: folliculogenesis development of the follicle within oocyte development (oogenesis, hormone production, theca cells make androgens from cholesterol (blood, granulosa cells make oestradiol from androgen (theca, two cell theory.
