Lecture 9 Flashcards
what is sexual reproduction?
-the creation of an offspring by the fusion of a male gamete and female gamete to form a zygote
what is asexual reproduction?
-the creation of offspring without the fusion of a male and female gamete
-one parent clones offspring
what is the male gamete?
-sperm
what is the female gamete?
-egg
by what type of reproduction do most invertebrates reproduce?
-asexual
-typically by fission
what is fission?
-the separation of a parent into 2 or more individuals of similar size
what are 4 main methods of asexual reproduction?
-binary fission
-budding
-fragmentation
-parthenogenesis
what is binary fission?
-seperation of the parent cell into 2 new daughter cells
what is budding?
-new individuals arising from outgrowths of existing individuals
what is fragmentation?
-breaking of the body into pieces
-some or all will develop into adults
-must be accompanied by regeneration (regrowth of lost body parts)
what is parthenogenesis?
-the development of a new individual from an unfertilized egg
-mainly in invertebrates
-rarely in vertebrates
what is the two fold cost of sexual reproduction?
-sexual females will have half as many daughters as asexual females
do almost all eukaryotic species reproduce sexually?
-YES
what does sexual reproduction result in?
-genetic recombination
what are the potential advantages of genetic recombination?
-increase in variation (increase in reproductive success of parents in changing environments)
-increase in the rate of adaptation
-shuffling of genes (possible elimination of harmful genes from a population)
what type of reproduction is expected to be the most advantageous in a stable environment? what about a variable environment?
-stable = asexual reproductive (less genetic variation)
-variable = sexual reproduction (more genetic variation)
what is ovulation?
-the release of mature eggs at the midpoint of a female cycle
what do most animals reproductive cycles relate to?
-the changing seasons
what controls reproductive cycles?
-hormones
-environmental cues
do animals solely sexually reproduce or asexually reproduce?
-NO
-they may alternate the methods
what is a solution for organisms that may struggle to encounter mates? what is an example of an organism that has this solution?
-hermaphroditism
-earthworms
what is hermaphroditism?
-an individual has both male and female reproductive systems
-can produce both gametes
-some of these organisms can self-fertilize
what is the term for self fertilization?
-autogamy
what are sex reversals?
-some species will undergo sex reversals
-male to female reversal (certain oysters)
-female to male reversal (coral reef fish)
what is external fertilization?
-the eggs are shed by a female and fertilized by sperm in the external environment
-need a moist environment
what plays an important part in sexual reproduction?
-mechanisms of fertilization
-union of egg and sperm
what is internal fertilization?
-sperm are deposited near the female reproductive tract
-fertilization occurs within the tract
what does internal fertilization require?
-behavioural interactions
-compatible sexual organs
what is required by all types of fertilization?
-critical timing
-mediated by environmental cues, pheromones, courtship behaviour
do species with external fertilization or internal fertilization produce more gametes?
-species with external fertilization
what is true for all species no matter the type of fertilization they perform?
-produce more offspring than their immediate environment can handle
-proportion that survives is small
what can species with internal fertilization provide?
-greater protection of embryos
-more parental care
what do the embryos of some terrestrial animals develop in?
-amniote eggs
-calcium + protein containing shells
-several internal membranes
what helps to ensure the survival of offspring?
-parental care
what are gonads?
-organs that produce gametes
what do simple systems have instead of gonads?
-formation of gametes from undifferentiated tissue
what will more complex systems have in addition to gonads? what is their role?
-sets of accessory tubes and glands
-to carry, protect, and nourish gametes + developing embryos
what is copulation?
-sexual intercourse
what is an extra part of an insects female reproductive system?
-spermathecae
-stores sperm during copulation
what does the reproductive tract of a vertebrate release?
-sperm, ova, and offspring
what is the cloaca in nonmammalian vertebrates?
-common opening between the external environment and the digestive, excretory, and reproductive systems
how many ovaries are in the vertebrates female reproductive system?
-typically 2
-in some species one of the ovaries never develops
how many uterus’ do mammals such as marsupials have?
-2 separate uteri
where do differences in male reproductive systems mainly exist?
-the copulatory organs
what type of mating is relatively rare among animals? what have some species done to decrease this?
-monogamy
-have evolved mechanisms
what are the males external reproductive organs?
-scrotum
-penis
what are the males internal reproductive organs?
-the gonads
-accessory glands
-ducts
what is the role of the gonads in the male reproductive system?
-to produce sperm and hormones
what is the role of the accessory glands in the male reproductive system?
-secrete products needed for sperm movement
what is the role of ducts in the male reproductive system?
-carry sperm and glandular secretions
what do the testes consist of?
-highly coiled tubules surrounded by connective tissue
what are the highly coiled tubules in the testes?
-seminiferous tubules
why are the testes typically held outside of the abdominal cavity? where are the testes usually?
-production of sperm cannot occur at normal body temp
-testes are usually in the scrotum because the temperature will be lower
after the sperm pass through the seminiferous tubules where do they go?
-coiled tubules of the epididymis
what is the pathway of sperm during ejactulation?
-propelled through the muscular vas deferens and the ejaculatory duct
-exit the penis through the urethra
what is semen composed of?
-sperm
-secretions from 3 accessory glands
what accessory gland contributes most of the volume of semen?
-the 2 seminal vesicles
how does the prostate gland secrete its products?
-directly into the urethra through several small ducts
what do the bulbourethral glands secrete?
-clear mucus before ejactulation
what is the purpose of the clear mucus secreted from the bulbourethral glands?
-neutralize acidic urine that remains in the urethra
what is the human penis composed of?
-3 cylinders of spongy erectile tissue
what happens to the erectile tissue during sexual arousal?
-fills with blood from arteries
-causes an erection
what can be said about the head/glans of the penis?
-thinner skin than the shaft
-more sensitive to stimulation
-surrounded by a fold of skin called the prepuce/foreskin
what are the external reproductive structures of the female reproductive system?
-clitoris
-2 sets of labia
what are the internal organs of the female reproductive system?
-pair of gonads
-a system to ducts and chambers
what is the purpose of the ducts and chambers within the female reproductive system?
-carry gametes
-house the embryo + fetus
what are the female gonads?
-the ovaries?
where do the ovaries lie?
-in the abdominal cavity
what does each ovary contain?
-many follicles
-follicles consist of a partially developed egg surrounded by supporting cells
what is the name for a partially developed egg?
-oocyte
how does the egg travel from the ovary to the uterus?
-via an oviduct or fallopian tube
-cilia in the oviduct help move the egg
what is the uterine lining? what does it contain?
-endometrium
-contains many blood vessels
what happens to the uterus as it is closer to the external environment?
-narrows at the opening called the cervix
-opens into the vagina
what is the vagina?
-a muscular but elastic chamber
-is the repository (storing place) for sperm during copulation
-serves as the birth canal
where does the vagina open to the outside?
-the vulva
what does the vulva consist of?
-labia majora
-labia minora
-hymen
-clitoris
what parts of the internal/external female reproductive system are rich with blood vessels?
-vagina
-labia minora
-clitoris
what can be said about the clitoris?
-has many nerve endings (high sensitivity)
-has a head/glans covered by the prepuce (small hood of skin)
what is important to mammalian reproduction but are not apart of the female reproductive system?
-mammary glands
what within the mammary glands secretes milk?
-small sacs of epithelial tissue
when will a human embryo begin to show distinctive features?
-7 weeks after conception
will embryos of different species have common features during early stages?
-YES
-share basic mechanisms of development
-common set of regulatory genes
what do biologists use to study development?
-model organisms
what initiates embryonic development?
-fertilization
-cleavage
what is fertilization?
-formation of a diploid zygote from a haploid egg and sperm
what 2 things play a crucial role in the steps of fertilization?
-molecules
-events at the eggs surface
what are the 2 basic steps of fertilization?
-sperm penetrates the protective layer around the egg
-receptors on the egg surface bind to molecules on the sperm surface
what do the changes at the eggs surface prevent?
-polyspermy
what reactions are triggered when the sperm meets the egg?
-the acrosomal reaction
-the cortical reaction
what is polyspermy?
-the entry of multiple sperm nuclei into the egg
what is the acrosomal reaction?
-the acrosome at the tip of the sperm releases hydrolytic enzymes that digest the material around the egg
what does gamete contact/fusion do to the eggs cell membrane?
-depolarizes it
-sets up a fast block to polyspermy
what is required for the cortical reaction? what triggers the cortical reaction?
-high concentration of calcium within the egg
-a change in the calcium concentration + sperm binding to a receptor in the zona pellucida
how is the fertilization envelope formed?
-vesicles beneath the eggs plasma membrane release their contents (calcium)
-calcium contributes to the appearance
what does the rise of calcium in the cytosol of the egg increase?
-rates of cellular respiration
-protein synthesis done by the egg
when does cell division being within the egg?
-when the sperm nucleus merges with the egg nucleus
do the proteins and mRNAs needed for activation need to be synthesized within the egg?
-NO
-they are already present within the egg
what is the cortical reactions purpose?
-the slow block to polyspermy
what is the zona pellucida? how must the sperm get there?
-the extracellular matrix of the egg
-travel through a layer of follicle cells
what is the acrosomal reactions purpose?
-fast block to polyspermy
when does the diploid nucleus form in mammals?
-after the first division of the zygote
when does the first cell division occur in mammals?
-12-36 hours after sperm binding
what is cleavage?
-a period of rapid cell division without growth
-follows fertilization
what are the cleavage cells called?
-blastomeres
what is the blastula?
-ball of cells with a fluid filled cavity
-in most mammals, human equivalent is a blastocyst
what is the fluid filled cavity of the blastula called?
-blastocoel
what are the cleavage patterns of frogs and other land animals? why?
-asymmetric
-the distribution of yolk (stored nutrients)
what are the two poles during cleavage a lot of mammals? what distinguishes them?
-vegetal pole (more yolk)
-animal pole (less yolk)
how is the rate of cell division after cleavage?
-rate slows down
-normal cell cycle is restored
what is morphogenesis?
-the process by which cells occupy their appropriate locations
-gastrulation + organogenesis involved
what is gastrulation?
-movement of cells from the blastula surface to the interior of the embryo creating a 3 layered embryo called a gastrula
-gut formation
what is organogenesis?
-formation of organs
do humans have much egg yolk?
-NO
what is the inner cell mass in humans?
-cluster of cells at one end of the blastocyst
what is the trophoblast?
-outer epithelial layer of the blastocyst
-does not contribute to the embryo
-initiates implantation
what happens to the trophoblast after implantation?
-continues to expand
-forms a set of extraembryonic membranes
what is the purpose of the extraembryonic membranes formed from the trophoblast?
-enclose specialized structures outside of the embryo
what does gastrulation in humans involve?
-inward movement from the epiblast
how was the colonization of land by vertebrates made possible?
-evolution of shelled bird and reptile eggs as well as egg laying mammals (monotremes)
-evolution of the uterus in marsupials + eutherian animals
what is the embryo surrounded by no matter the adaptations?
-a fluid sac called the amnion
what is the role of the amnion in animals who lay their eggs on land?
-protects the embryo from desiccation
-allows for reproduction on dry land
-why these animals are called amniotes
what are the four extraembryonic membranes and their functions?
-chorion (gas exchange)
-amnion (encloses amniotic fluid)
-yolk sac (encloses the yolk)
-allantois (disposes of waste products + gas exchange)
what occurs during organogenesis?
-various regions of the germ layers develop into rudimentary organs
what is specific to early vertebrate organogenesis?
-notochord forms from the dorsal mesoderm
-signalling molecules secreted by the notochord and other mesodermal cells induce the neural plate to form
what is the neural plate formed from?
-ectoderm
what does the neural plate eventually form?
-forms the neural tube by curving inwards
what does the neural tube become?
-the central nervous system
even though the notochord disappears before birth, how is it still important/present?
-contributes to parts of the discs between vertebrae
what causes cell shape changes? what is an example?
-movement of parts within a cell
-microtubules + microfilaments of the cytoskeleton contribute heavily
-ex: neurulation, microtubules oriented from dorsal to ventral in a sheet of ectodermal cells help lengthen cells along that axis
what is apoptosis?
-programmed cell death
-individual cells, sets of cell, or whole tissues stop developing and become engulfed by neighbouring cells
what is an example of where apoptosis is used in early development?
-more neurons are produced than needed in developing embryos
-extra neurons are removed by apoptosis
what is an example of where apoptosis is used during metamorphosis?
-a structure functions in early stages + not later ones
-the tail of a tadpole undergoes apoptosis
