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BIO270H1 Final: BIO270 Final Exam Study Notes

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Christopher Garside
Study Guide

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BIO270 Final Exam Study Notes
Lecture #6 - Reproduction
Elements of sexual reproduction:
- sex determination
- gametogenesis
- mating
- fertilization
- development
- generates genomic variation at three levels:
1) haploid gametes from a diploid parent
- spermatogenesis in males (sperm)
- oogenesis in females (ova)
2) recombination creates hybrid chromosomes
3) diploid offspring unique genetic combinations
- creates population with distinct genotypes
- sexual reproduction does not require genetically separate sexes
- capacity to produce both eggs and sperm
- simultaneous hermaphrodites can produces eggs and sperm at same time (eg. worm)
- serial hermaphrodites can change sex in response to environmental cues
- protogynous = females become males - social factors? (eg. eel)
- protandrous = males become females - hormones? (eg. nemo fish)
Asexual Reproduction:
- advantageous for animals living in constant, stable environment
- identical offspring with same genetic material as parent
- binary fission - parent organism divides in two by mitosis
- budding - buds form from somatic tissue; allows single individual to produce a colony (eg. coral)
- parthenogenesis - ova and female reproductive system; no male gamete required, no fertilization
- fragmentation - new organism grows from fragment of parent
Sex determination by genotype:
- mammals - presence of Y chromosome (sex-determining chromosome)
- Heterogametic male (XY), homogametic female (XX)
- birds - heterogametic female (ZW), homogametic male (ZZ)
- honeybee - haplo-diploidy
- fertilized egg becomes diploid females and unfertilized eggs become haploid males
Sex determination by environment: temperature dependant sex determination (TSD)
- common in reptiles
- temp of egg incubation alters sex of offspring
- pivotal temperature - equal number of males & females result
- may also be affected by hormone levels in egg - vary with season

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- three modes of reproductive strategies determined by fate of ova prior to & after fertilization
1) Oviparous animals
- ova expelled from body and all development occurs externally using resources of egg
- fertilization can be external (fish) or internal (birds and reptiles)
2) Viviparous animals
- young develop within female body
- fertilization internal
- derive nutrition directly from placenta
- mammals and sporadically in many other taxa
3) Ovoviviparous animals
- young develop within female, but derive nutrition from the yolk
- egg hatches within mother
- fertilization internal
- sharks, reptiles, and many invertebrates
Gametogenesis: occurs in gonads - meiosis
- females: oogenesis; ovaries produce large gametes (ova)
- males: spermatogenesis; testes produce small gametes (sperm)
Oogenesis: production of ovum/egg
- ovary composed of ova-producing oogonia and
surrounding somatic cells
- oogenesis progresses to primary oocyte stage early in
female's life, but final steps delayed until later
- follicle cells orchestrate oogenesis by paracrine factors and
cell to cell contacts
- vertebrate oocytes grow by accepting material from
somatic follicle cells
- eggs of aquatic animals permeable to water
- fish and amphibians produce simple gelatinous eggs that receive a viscous coating
- eggs of terrestrial animals must resist dehydration
- reptiles and birds have eggs with hardened shells of calcium carbonate
- placental (eutherian) and marsupial (metatherian) mammals
- no eggshell
- challenges of terrestrial life solved by rearing ova internally
- all terrestrial vertebrate embryos are enclosed in a fluid filled compartment (amnion)

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- embryo of amniotes produces four
sheets of cells that surround the embryo
folliculogenesis: prior to ovulation, some follicles stimulated to mature
Spermatogenesis: production of sperm
- in most species, males produce sperm continuously from maturation until late in life
- spermatozoa are produced in seminiferous tubules in tests
- seminiferous tubules contain several cell types:
- spermatogenic cells: spermatozoa in various stages of development
- sertoli cells: between spermatogenic cells; regulate spermatogenesis; androgen binding
protein; inhibin
- leydig cells: interstitial cells; produce testosterone
Sperm Maturation:
- spermatids become sperm
- lose much of their cytoplasm
- develop flagellum with abundant mitochondria at its base
- condense DNA in nucleus
- nearly mature spermatozoa released into the lumen of the tubule
- cannot swim
- sperm stored in the epididymis where they mature further
- gain the capacity to swim
Sperm Release:
- during ejaculation, sperm propelled by cilia or smooth muscle contractions along the vas deferens
which connect to the urethra
- seminal fluid added to sperm by exocrine glands during ejaculation
- seminal vesicles - produce alkaline fluid with nutrients and regulatory factors (eg. prostaglandins)
- prostate - secretes nutrients, mainly citrate
- bulbourethral gland - secretes mucus as a lubricant
- in some species (eg. mammals) sperm only capable of fertilizing an egg after entering female
reproductive tract (capacitation)
Copulatory Organs: most species that use internal fertilization possess some form of copulatory
(intromittant) organ to increase efficiency of sperm transfer
- birds are an exception (cloacal kiss)
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