19-1 copyright 2010 mcgraw-hill australia pty ltd powerpoint slides to accompany biology: an...

19-1Copyright 2010 McGraw-Hill Australia Pty Ltd PowerPoint slides to accompany Biology: An Australian focus 4e by Knox, Ladiges, Evans and SaintSlides prepared by Karen Burke da Silva, Flinders University

Part 4: Animal form and function

Chapter 19: Animal reproduction


Reproduction• Asexual reproduction

– one parent– new individuals genetically identical to parent and to each

other

• Sexual reproduction– two parents– new individuals genetically unique (novel combination of

genes from both parents)


Asexual reproduction• New individuals produced through mitotic cell

division• Limited genetic diversity• Occurs by:

– regeneration– budding– parthenogenesis


Regeneration• Production of new individuals

– cellular replication by mitosis– differentiation of tissues

• Reproduction by fragmentation– example: aquatic annelids

• Regeneration of individuals from body parts– example: starfish


Budding• Production of new individuals

– outgrowth of body wall of parent

• Break off to form individual– example: Hydra

• Remain attached to form

part of colony– example: corals


Parthenogenesis• Production of new individuals

– egg cells develop into embryos without fertilisation– offspring usually female

• Obligate parthenogenesis– example: Heteronotia binoei (Binoe’s gecko)

• Cyclical parthenogenesis– example: some species

of aphids


Parthenogenesis (cont.)• Ants, bees and wasps (Hymenoptera)

– females produced by sexual reproduction– males produced by asexual reproduction

(parthenogenesis)

• Unfertilised eggs (n)– undergo mitosis, but do not divide into two cells– nuclei fuse to produce a diploid cell (2n)– cell develops as if fertilised


Sexual reproduction• New individuals produced through fusion of haploid

cells (gametes) from parents– egg (ovum)– sperm (spermatozoon)

• Increases genetic diversity


Gametes• Two types of gametes• Similar structure

– isogamy

• Different structure– anisogamy– smaller of gamete pair = male

Fig. 19.5a & d: Gametes



Male and female• Different mating types = sex

– male, female

• Males– produce sperm only

• Females– produce eggs only


Mating systems

• Organisms with separate sexes– dioecious

• Organisms with both sexes in one individual– monoecious or hermaphroditic


Hermaphroditism• Hermaphrodites produce both male and female

gametes• Problems of self-fertilisation limited by separation

of male and female gametes– anatomy

male and female reproductive tracts separate

– behaviour complex courtship and mating

– time eggs become fertile after sperm are no longer functional sex change


Changing sex• Some species avoid self-fertilisation by sex

changes– alternate between male and female at different stages of

life cycle

• Protandry: male female– Example: clownfish

• Protogyny: female male– Example: parrot fish


Reproductive strategies• Developmental strategies vary• Indirect development

– offspring pass through one or more larval stages before they attain adult form

• Direct development– offspring hatch or are born resembling miniature adults


Indirect development• Many eggs produced

– small amount of yolk in each egg– limits time for embryonic development

• Free-living larval forms• Metamorphosis (change in form from larva to

adult)– examples: butterflies, flies, beetles, frogs

Fig. 19.8: Indirect development



Direct development• Few eggs produced

– large amount of yolk in each egg– embryo nourished by yolk

• Embryo develops in egg• Hatches/born with adult form

– examples: land snails, reptiles, birds, mammals


Fig. 19.9: Direct development

Copyright © 18.9 Jan Aldenhoven/AUSCAPE


Development in mammals• Direct development

– but eggs have small amount of yolk

• Young develop in uterus• Nutrients provided to developing young

– before birth uterine secretions placenta

– after birth milk


Development in mammals (cont.)• Variation in patterns of reproduction

– young born at different stages of development

• Marsupials and eutherians– live young (viviparous)


Development in mammals (cont.)• Monotremes

– lay eggs (oviparous)


The costs of sexual reproduction• Parental investment in reproduction

– varies depending on reproductive strategy

• Includes– production of gametes– increased risk of predation– competition for mates– parental care

• Cost must not outweigh benefit• Caring for young

– increases chances of offspring surviving to maturity– reduces ability of one (or both) parents to find food and

avoid predators

Question 1:What benefits of sexual reproduction would outweigh the costs?

a) Increased ability to produce genetic diversity

b) Ability to produce variable offspring which could have a greater chance of success in a new environment

c) Reduction in deleterious mutations having an effect on offspring

d) All of the above



Gametogenesis• Primary sex organs = gonads• Male gonad = testis

– produces sperm (spermatozoa)

• Female gonad = ovary– produces eggs (ova)

• Process of gamete production = gametogenesis– spermatogenesis– oogenesis


Mitotic divisions• Primordial germ cells undergo a series of mitotic

divisions• Give rise to multiple diploid (2n) oogonia/

spermatogonia• After the final mitotic division, these cells are

termed oocytes/spermatocytes


Meiotic division• Primary oocyte (product of mitotic divisions)• First meiotic division

– primary oocyte gives rise to secondary oocyte first polar body

• Second meiotic division– secondary oocyte gives rise to

ovum (egg) second polar body

– first polar body gives rise to polar bodies


Meiotic division (cont.)• Primary spermatocyte (product of mitotic divisions)• First meiotic division

– primary spermatocyte gives rise to secondary spermatocytes

• Second meiotic division– secondary spermatocytes give rise to

spermatids


Fig. 19.20a: Oogenesis


Fig. 19.20b: Spermatogenesis


Maturation of gametes• Spermatocyte

– loss of most of cytoplasm– development of long flagellum (tail)– formation of secretory acrosome at anterior of head

section

• Oocyte– increase in organelles– increase in nutritive materials– development of protective extracellular membranes, e.g.

vitelline membrane


Fertilisation• Fusion of egg and sperm• Egg activation

– inactive egg is activated by fusion of plasma membranes of egg and sperm

– resumes synthetic activity

• Nuclear fusion– pronuclei of egg and sperm fuse– creates diploid zygote

Fig. 19.25: Fertilisation



Methods of fertilisation• Methods of bringing egg and sperm together• External fertilisation

– takes place outside body– examples: corals, frogs

• Internal fertilisation– takes place inside body– examples: land snails, mammals


Internal fertilisation• Sperm must be transferred to female reproductive

tract• Intromittent organ

– penis, claspers

• Spermatophore– packet of sperm

• Injected through body wall– example: leeches

Question 2:

Which of the following is/are disadvantages of internal fertilisation?

a) gametes and embryo will be prevented from desiccation

b) independence from external water source

c) complicated behaviour must be evolved to bring the male and female into intimate contact

d) the need for an intromittent organ


Summary• Asexual reproduction means having a single

parent• Sexual reproduction requires two parents• Reproduction can be costly• Successful reproduction between male and female

animals requires the proper timing and control of a complex sequence of events

• Animals employ different strategies to maximise their chances of reproductive success


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