Sexual versus asexual reproduction

Asexual reproduction offspring genes all come from one parent Produce genetic clones

Sexual reproduction offspring are fusion of male gametes (sperm) and

female gametes (eggs) to form zygotes Produce hybrids

Mechanisms of Asexual Reproduction Fission

separation of a parent into two or more individuals of about the same size

This is obviously not an option for you

Budding new individuals

arise from outgrowths of existing ones

Mechanisms of Asexual Reproduction

Fragmentation body breaks into

pieces some or all develop

into adults accompanied by

regrowth of body parts

Mechanisms of Asexual Reproduction

Reproductive Cycles and Patterns

Most animals exhibit reproductive cycles related to changing seasons

Controlled by hormones, and environmental cues

Animals may reproduce asexually sexually Or alternate these methods

Parthenogenesis an egg develops

without being fertilized

Several fishes, amphibians, and lizards

Estrogen

Ovulation

Female-like

ProgesteroneO

vary

size

Time

Hor

mon

ele

vel

Ovulation

Beha

vior

Male-like

Female-like

Male-like

What if you never encounter a mate?

Rather a special problem, isn’t it?

Hermaphroditism each individual has male and female reproductive

systems sequential hermaphroditism - an individual reverses its

sex during its lifetime

Genitalpore

Male organs:

Seminalvesicle

Sperm duct(vas deferens)

Vas efferens

Testis

(Excretory pore)

(Digestive tract)

Female organs:

Uterus

Yolk gland

Yolk duct

Oviduct

Ovary

Seminalreceptacle

Eggs

You’ve decided to make it complicated…

Internal fertilization requires critical timing often mediated by environmental cues

pheromones and/or courtship behavior

Internal fertilization requires BOTH behavioral interactions and compatible copulatory organs

Primary germ cellin embryo

Mitoticdivision

Primaryoocyte

Ovary

Oogonium

DifferentiationOogoniumin ovary

Primaryoocytewithinfollicle

Growingfollicle

Secondaryoocyte

Completion of meiosis Iand onset of meiosis II

Ovulation

First polar body

Mature follicleEntry of spermtriggerscompletionof meiosis IISecond polar body

Ovum

Rupturedfollicle

Ovulatedsecondary oocyte

Corpus luteum

Degen-erating corpus luteum

Spermatogonium

Primary spermatocyte(in prophase of meiosis I)

Mitotic division, producinglarge numbers of spermatogonia

Meiosis I completed

Differentiation and onset of meiosis I

Secondary spermatocyte

Meiosis II

Earlyspermatids

Spermatids(at two stages ofdifferentiation)

Differentiation

Sperm cells Neck

Head Midpiece TailPlasma membrane

Mitochondria

Acrosome Nucleus

Sertoli cellnucleus

Lumen ofSeminiferous tubule

Cross sectionof seminiferoustubule

Testis

EpididymisSeminiferous tubule

Advantages Disadvantages

Asexual

Sexual

• little biological/energy cost (mitosis)

• offspring genetically identical;

• genetic variation(meiosis & 2 parents)

• high biological/energy cost- behaviors: courtship, mating,

nest building, care/nourishyoung

so species vulnerable to env

Advantages Disadvantages

Asexual

Sexual

• little biological/energy cost (mitosis)

• offspring genetically identical;so species vulnerable to env

• genetic variation(meiosis & 2 parents)

• high biological/energy cost- behaviors: courtship, mating,

nest building, care/nourishyoung

Advantages Disadvantages

Asexual

Sexual

• little biological/energy cost (mitosis)

• offspring genetically identical;so species vulnerable to env

• genetic variation(meiosis & 2 parents)

• high biological/energy cost- behaviors: courtship, mating,

nest building, care/nourishyoung

Advantages Disadvantages

Asexual

Sexual

• little biological/energy cost (mitosis)

• offspring genetically identical;so species vulnerable to env

• genetic variation(meiosis & 2 parents)

• high biological/energy cost- behaviors: courtship, mating,

nest building, care/nourish young

- dev specializedreproductive structures

Advantages Disadvantages

Asexual

Sexual

• little biological/energy cost (mitosis)

• offspring genetically identical;so species vulnerable to env

• genetic variation(meiosis & 2 parents)

• high biological/energy cost- behaviors: courtship, mating,

nest building, care/nourishyoung

- dev specializedreproductive structures

- sync timing of sperm/eggproduction; fertilize egg(s)