Bio 224

• what is asexual reproduciton?

  - result in genetically identical offspring

  - no genetic diversity
• what is sexual reproduction?

  - diploid individual (2n) produces haploid sex cells (n) (gametogenesis

  - haploid sex cells (n) unite to form new diploid individual (fertilization)

  - mixing of genetic material provides genetic diversity
• what is budding?


  - a new individual arises from an outgrowth of an older one

  - common in sponges and some cnidarians
• what is fission?


  - one individual separates into 2 or more individuals of about equal size

  - occurs in very primitive animals

  e.g. bacteria, some cnidaria
• what is fragmentation/regeneration?

  - individual breaks into small pieces

  - each pieces can form a new individual

  - have cells in every part of body that are totipotent, meaning they can differentiate into any other type of cell that occurs in their body

  - some cells must dedifferentiate

  e.g. echinoderms
• what is parthenogenesis?

  - development of an individual from an unfertilized egg

  - common in arthropods, some fish, amphibians and lizards

  - can be used for sex determination (e.g. ants, bees, wasps)

  - in bees females diploid (fertilization), males haploid (parthenogenesis)
• what is special aboutDaphinia

  - can alternate between sexual and asexual reproduction

  - live in water, when they molt the exoskeleton is released and babies are released into the water (asexual)

  - if under stress (not enough food, or oxygen in water), will switch to sexual reproduction, some of the babies will differentiate to male, others to female
• what is the advantage of being able to alternate between sexual and asexual reproduction?


  - can switch to sexual reproduction to increase genetic diversity

  - if all organisms are the same then they will be affected by negative pressures the same

  - but if they can create genetic diversity through sexual reproduction that won't be a problem
• what is hermaphroditism?

  organism has male and female reproductive systems
• what is simultaneous hermaphroditism?

  - have both ovaries and testes at the same time

  - reproduce with other individuals to get genetic variation (don't self fertilize)

  e.g. earthworm
• what is sequential hermaphroditism?


  - change sex at some point in life cycle

  - protogynous - female before male

  - protoandrous - male before female

  e.g. sea bass (protogynous), clownfish (protoandrous)
• how does sexual reproduction increase genetic variability?

  - independent assortment of homologous chromosomes during meiosis I

  - 1 homologue from each parent

  - more chromosomes = more combinations

  - e.g. human haploid # (n) = 23 so 2^23 = 8.3 million combinations

  - crossing over during Prophase I - mixing of genes

  - random fertilization

  - 8.3 million combinations in egg and sperm

  - 8.3 million x 8.3 million = 70 trillion combinations
• what is gametogenesis?


  - haploid gametes produced by germ cells in primary sex organs

  - females - ovaries produce eggs (ova)

  - large and non mobile

  - oogenesis

  - male - testes produce sperm

  - small and mobile

  - spermatogenesis
• what is spermatogenesis?

  - production of sperm

  - each diploid parent cell produces 4 sperm cells

  - each day 3 million primary spermatocytes develop from diploid cells

  - process occurs in seminiferous tubules
• what is the process of spermatogenesis?

  
• endocrine control of spermatogenesis


  - hypothalamus secretes GnRH (gonadotropin-releasing hormone)

  - triggers anterior pituitary to release LH and FSH

  - LH acts on Leydig cells --> cells produce male steroid hormones (sex hormones - testosterone)

  - FSH and testosterone stimulate Sertoli cells

  - Sertoli cells provide nutrition to developing sperm (spermatids)

  - results in spermatogenesis and secondary sex characteristics

  
• what is oogenesis?

  - production of ova

  - only 1 ovum produced in an ovarian cycle

  - full complement of primary oocytes present at birth and held dormant (in prophase I) until puberty
• what is the process of oogenesis?

  
• what is the journey of an oocyte?

  1. primary oocyte forms a cell layer, with this layer is called follicle

  2. the zona pellucida starts forming around the primary oocyte

  3. a fluid filled cavity (antrum) starts forming in the follicle's cell layer

  4. mature follicle is formed after meiosis I is complete, secondary oocyte and first polar body are formed

  5. at ovulation the mature follicle ruptures, releasing the secondary oocyte and first polar body

  6. a corpus luteum forms from remnants of the ruptured follicle

  7. the corpus luteum breaks down if woman doe not become pregnant

  
• endocrine control of oogenesis and ovulation

  - FSH stimulates one follicle to develop (complete meiosis I)

  - estradiol stimulates the growth and development of the oocyte (acts as positive feedback, anterior pituitary releases lots of FSH and LH)

  - burst of LH triggers ovulation, estrogen decreases after ovulation

  - progesterone prepares the uterus for receiving the embryo

  - when progesterone goes up it stops anterior pituitary from secreting LH and FSH so another follicle doesn't develop, if no fertilization, then LH and FSH are triggered again

  - if fertilization does occur the progesterone and estrogen levels stay relatively high to keep LH and FSH levels low so another follicle doesn't develop

  
• mating


  - anatomical and behavioural adaptations to bring gametes into close proximity for fertilization

  - behavioural adaptations - mating rituals

  - anatomical adaptation - secondary sex organs
• fertilization


  combining two haploid gametes to form a diploid zygote

  - internal or external
• why does external fertilization occur mainly in aquatic animals?


  in water so there is no risk of desiccation/dehydration
• what are the potential risks of external fertilization?

  cells become prone to predation, other animals can feed on them
• how do animals compensate for the potential risks of external fertilization?

  - produce large numbers of gametes (thousands)

  - assumption that some will survive and population will continue

  - also release gametes in synchronized fashion (female releases eggs, male releases sperm on top of eggs)
• what is the structure of an ovum?

  - nucleus at the centre (two nuclei if fertilized)

  - zona pellucida (egg coat in mammals)

  - glycoprotein outer-layer (jelly coat)
• what is the structure of a sperm?

  - head: nucleus, acrosome

  - midpiece: has mitochondria that produce ATP that allow beating of flagellum

  - tail

  - very little cytoplasm
• cellular mechanisms of fertilization

  1. acrosome releases hydrolytic enzyme, dissolves the jelly coat on the egg

  2. sperm-head binds to the receptor on the plasma membrane of the ovum (has actin protein, allows it to anchor)

  3. fusion of sperm and ovum plasma membranes, sperm nucleus enters the ovum

  4. activation of IP3-Ca2+ signaling pathway, separation and hardening of zona pellucida (fertilization membrane)

  5. fusion of two haploid nucleus to form a diploid nucleus
• what are the fast and slow blocks to polyspermy?


  fast block:- when sperm binds that depolarizes the egg cell (typically - charge inside), membrane potential changes from - to +, depolarization inhibits other sperm from entering into the egg. slow block:- cortical granules contain proteins, when sperm nuclei enters, triggers release of calcium from ER, so Ca concentration in cell increases, triggers cortical granules to fuse with membrane and release proteins outside of the cytoplasm, act with jelly coat to make impenetrable layer
• what prevents fertilization of an ovum by the sperm of a different species?

  - binding of protein head is species specific, so can only bind to ovum of the same species

  - receptors on eggs are called bouncer proteins because sperm from other species bounces off (can only bind with sperm of the same species)
• what prevents polyspermy?

  fast and slow block processes
• what is the benefit of external development?

  - less energy requirement

  - develops outside of mother

  - embryo is self sufficient in terms of energy requirement

  - however doesn't have parental protection
• what is the benefit of internal development?


  - more protection

  - develops within the mother

  - energetically more expensive
• what is oviparous reproduction?


  - lay eggs, no support from parent

  - evolution of amniotic egg

  - develops within fluid filled sac called amniotic sac

  e.g. birds
• what is viviparous reproduction?


  - live young, nutrients, gases etc. from parent

  e.g. most mammals
• what is ovoviviparous reproduction?


  - young develop in an egg inside parent often with live birth but little maternal support

  e.g. some insects, sharks, snakes
• what are the main advantage and disadvantage of oviparity?

  - less energetically expensive for mother (pro)

  - more prone to predation (con)
• how does the embryo receive nutrition and oxygen in oviparity?


  - embryo grows within calcareous shell, egg is full of nutrients

  - calcareous shells are permeable to respiratory gases

  - shells also permeable to moisture
• why do fertilized eggs of aquatic animals not have shells?

  - calcareous shells protect from desiccation, which is not a problem for aquatic animals

  - no risk of desiccation when development is in the water
• what are the main developmental stages?

  1. fertilization

  - forms zygote

  2. cleavage

  - cells divide very rapidly into morula (solid ball of cells

  - differentiates into ball with hollow cavity

  - blastula (hollowed ball of blastomeres - embryo)

  - blastocoel becomes main body cavity

  3. gastrulation

  - gastrula with primary tissue layers (endoderm, mesoderm, ectoderm)

  4. organogenesis

  - major tissue and organ systems

  5. metamorphosis

  - adult characteristics

  - cells differentiate into organs and tissues that complete development