Reproduction

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asexual

Back 1

production of individuals without use of gametes

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sexual

Back 2

production of new individuals by the union of gametes-ususally two different parents

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advantages of asexual

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-only need one to reproduce
-no genetic change: good IF environment is stable
-all individuals are producing offspring
-more efficient at passing on genes

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disadvantages of asexual

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-no recombination of genes

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asexual in unicellular

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fission- mitosis

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asexual in multicellular

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budding
gemmulation
fragmentation
parthenogenesis

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advantages of sexual

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-genetic recombination

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genetic variability comes from:

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-exchange of genes between chromosomes during crossing over

-shuffling of homologous chromosomes in meiosis

-random fusion of gametes

***favorable when environment is not stable***

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disadvantages of sexual reproduction:

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-typically need two parents

-genetic recombinations is counter productive if conditions are stable

-only half the individuals are producing offspring

-less efficient at passing on genes

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types of sexual reproduction

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-bisexual: union of gamette from male and female

-dioecious: individuals either male or female

-monoecious: each individual produces sperm AND egg (hermaphrodites)

-sequential hermaphrodism: individual CHANGES SEX during life. Usually male then female.

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somatic cells

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cells that make up the BODY of an individual

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Gametes

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haploid sex cells (usually sperm and egg)

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primordial germ cells

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cells that give rise to gametes through the process of meiosis and cytokinesis

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primary sex organs

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where gametes are produced

(GONADS)

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accessory sex organs

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penis and vagina

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syngamy

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the union of two gametes (scientific term for fertilization)

*forms zygote

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gametogenesis

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process of gamete production

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spermatogenesis

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formation of sperm in the coiled tubes of the testes called seminiferous tubules

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spermatogonia (2n)

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-diploid

-divides by mitosis

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primary & secondary spermatocyte (2n)

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-diploid

-go through the 1st and then 2nd division of meiosis to create 4 sperm

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sperm (n)

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found in lumen of seminiferous tubule

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sertoli cells

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in seminiferous tubules

**nourish sperm cells

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characteristics of mature sperm

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head: acrosome, nucleus

midpiece: mitochondria

tail: flagellum

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oogenesis

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formation of the ovum in the ovary

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oogonia (2n)

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primordal germ cell

diploid

divides by mitosis

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primary and secondary oocyte (2n)

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primary- undergo meiosis 1
*unequal cytokenesis-results in 1 secondary oocyte (n)

secondary- undergo meiosis 2
*unequal cytokenesis- results in 1 (n) ovum

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for every one oocyte you get _______ functional ovum

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ONE

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polar bodies

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??????

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meiosis 1 begins in _____________
meiosis 2 isn't complete until _________________

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-developing embryo

-after sperm enters egg

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fertilization can be _____ or ________

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internal or external

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external fertilization

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sperm and egg are expelled from body

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internal fertilization

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sperm transfered from male to female
*common in invertebrates

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path of sperm

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urogenital system

1-sperm produced in testes
2-stored in epididymis
3-vas deferens
4-cloaca OR urethra (structure for transferring sperm)
5-urethra

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path of ovum

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1-produced in follicles in ovary (release=ovulation)
2-egg enters oviduct
3-zygote enters uterus

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spermatheca

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???????????

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oviparous

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release their eggs into the environment before fertilization or after fertilization

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ovoviviparous

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retain the fertilized egg internally but do not supply any additional nutrients to the zygote

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viviparous animals

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animals that retain zygote in the mother who provides nourishment to the developing young (MAMMALS)

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hormones

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molecules in body produced in one part to stimulate a response in another part

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male sex hormone

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testosterone: produced in the leydig cells fond between the seminiferous tubules of testes

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female sex hormones (plural)

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hormones from brain and ovaries function to control the release of gametes AND the state of the uterus

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estrus cycle

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reproductive cycle of most mammals (estrus=heat)

*females ONLY receptive to copulation during estrus

*lining is absorbed by body if no pregnancy

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menstrual cycle:

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reproductive cycle found in monkeys, apes, and humans.

*lining is shed if no pregnancy (menstration)

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pituitary gland of brain produces

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follicle-stimulating hormone (FSH)

luteinizing hormone (LH)

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hCG

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hormone produced by developing embryo (detected on pregnancy test)

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layers of the outer covering of mature egg (sea urchin)

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-jelly layer
-vitelline envelope
-plasma membrane

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Polyspermy

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fertilization of an egg by more than one sperm

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prevention of polyspermy

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1. fast block-change in charge across plasma membrane preventing other sperm getting in

2. cortical reaction- vitelline envelope is pushed away from membrane

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stages of development

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1. zygote
2. cleavage stage- zygote divides by mitosis
3. blastula-hollow chamber develops in the center of the morula-blastoceol
4. gastrulation- some cells form primary gut
5. Neurogenesis- nerve cord develops (only in chordata)
6.Organogenesis- formation of organs

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isolecithal egg

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little yolk, yolk evenly distributed

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mesolecithal egg

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moderate amount of yolk

-vegetal pole: hemisphere of egg with most yolk
-animal pole: hemisphere of egg with least yolk

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telolecithal egg

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large amount of yolk, unevenly distributed.

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patterns of cleavage

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differences in the amount and distribution of yolk will affect hoe cleavage proceeds

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holoblastic cleavage

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cytokinesis diides cell in two

*in isolecithal and mesolecithal eggs

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meroblastic cleavage

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cytokinesis does not divide yolk of the egg

*in telolecithal eggs

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radial cleavage

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as cells divide, cells appear stacked parallel to a central axis

*characteristic of deutrostomes

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spiral cleavage

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as cells divide, the stacked layers lie in the furrows from the layer below

*characteristic of protostomes

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enterocoelous

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mesoderm froms as pouches off the archenteron

*deuterostomes

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schizocoelous

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mesoderm cells develop aroudn teh base of the archenteron

*protostomes

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meroblastic cleavage

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cleavage only occurs in the active cytoplasm-results in layers of cells

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primitive streak

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groove down central axis of blastodisc

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neurogenesis

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development of the nerve cord from ECTOderm tissue