Reproduction Flashcards
What is asexual reproduction?
- offspring inherits all genetic material from a single parent
- Clone (not always)
- Formed by mitotic division
what is sexual reproduction?
- Offspring inherits genetic material from two parents
- Genetically unique individual
- Different from the parents and their siblings
what are the 3 forms of asexual animal reproduction?
- Forming a bud or protrusion
- fragmentation
- parthenogenesis
describe forming a bud, or a protrusion
bud, or protrusion, that eventually breaks off to form a new organism → eg hydra → simple mitotic divisions → bud is identical to the parent
describe fragmentation
splitting of one organism into pieces, each of which develops into a new individual → eg starfish → will eventually reach the original size
describe parthenogenesis
females produce eggs that are not fertilised by divide by mitosis and develop into new individuals → eg komodo dragon → mother produces eggs that are diploid → diploid egg would undergo division → offspring would be genetically identical to the mother
what is meitotic parthenogenesis?
- some types of parthenogenesis which use meiosis → not necessarily genetically identical
- komodo dragon gave birth to offspring despite not being in contact with another komodo dragon
what are the features of sexual reproduction?
- Meiosis and fertilisation
- Segregation of homologous chromosomes → generation of haploid gametes
- Fertilisation → one male and one female gamete fuse to form a diploid zygote
what is the female sexual reproductive cell?
ova
what is the male sexual reproductive cell?
spermatozoa
what are the disadvantages of sexual reproduction?
- Finding and attracting mates takes time and energy
2. Slower increase in population size
how does sexual reproduction lead to genetic diversity?
- During meiotic division there is recombination
- Random segregation of homologous chromosomes
- Fusion of two genetically unique gametes
what are the advantages of sexual reproduction?
- Allows for rare beneficial mutation arising in different organisms can be brought together
- Harmful mutations can be removed more quickly → not all mutations are given to all of the offspring
- Mechanism of defence parasites → a lot of genetic diversity more likely that some members of the population will be resistant
why is the phylogenetic quite young in evolutionary terms?
Any population that arose earlier would have died couldn’t have adapted to the environmental changes
what organism can reproduce both sexual and asexually?
Daphnia
describe reproduction in a daphnia
Type of reproduction depends on environmental conditions
Can form cysts to resist harsh conditions
Parthenogenetic cycle → mitosis → can produce both female and male offspring
Favourable conditions → parthenogenesis
When it gets colder and less food → sexual reproduction
what are the 2 sexual reproduction strategies?
- external fertilisation
2. internal fertilisation
describe external fertilisation
Gametes are released into the environment and then fertilised
Many animals who live in water do this
To increase chances of fertilisation = large gamete number, release of gametes in the same location and at the same time
Animals with external fertilisation are usually r-strategists
describe internal fertilisation
- adaptation for living on land
- can be oviparous
- vivparous
- usually k-strategists
what is meant by oviparous?
egg laying → contains amnion allows the embryo to develop in an aqueous environment → yolk sac has nutrients to support development → allantois which collects waste metabolic products → chorion surrounds the entire egg → surrounded by a hard shell
what is meant by viviparous?
giving birth to live young → can exchange via the placenta → nutrients sent through and waste products sent out
what are r-Strategists?
- Production of large numbers of offspring without provision of a lot of parental care
- Evolve in unstable, changing, unpredictable environments
what are k-Strategists?
- Production of few offspring and provision of a lot of parental care
- Evolve in stable, unchanging, predictable environments with limited resources
what is the role of the male reproductive system?
production and delivery of sperm
where are male gametes produced?
in the testes - which are located in the scrotum
where are male gametes stored?
travel to the epididymis - sperm matures and can be store heere
what happens the sperm during ejaculation?
move via the vas deferens into the penis
how does the sperm move in the male reproductive system?
- doesnt swim
- controlled by contractions
- smooth muscle in the walls of the vas deferens
what happens as sperm move?
substances are added by glands
what is the seminal vesicle?
releases a protein and sugar rich fluid which is added to the sperm - provides nutrients and energy
what is the prostate gland?
secretes an alkaline fluid - counteracts the acidity of the female reproductive system
what is the bulbourethral gland?
secretes a fluid which lubricates the urethra and facilitates the passage of the sperm
what are the tubes inside of the testes?
seminiferous tubules - sperm develop inside of here
what are found inside the seminiferous tubules?
sperm precurosr cells and sperm which are released into the lumen
what happens as sperm mature?
they move closer and closer towards the lumen of the seminiferous tubules
what toher cells can be found in the seminiferous tubules?
Sertoli cells
myoid cells
what do sertoli cells do?
nourish and protect the sperm. regulate spermatogenesis
what are myoid cells?
contractile cells. involved in transport along the seminiferous tubule
how much sperm do males produce per day?
200 - 300 million
what is spermatogenesis?
process by which haploid spermatozoa develop from germ cells in the seminiferous tubules of the testis
where does spermatogenesis start?
- primordial germ cell (in embryo)
- gives rise to spermatogonium (these are stem cells)
- starts self-renewal
what happens in spermatogenesis during puberty?
- in addition to self-renewing they give rise to primary spermatocyte
- goes through meiotic division
what does the first meiotic division in spermatogenesis result in?
secondary spermatocyte
what does the second meiotic division in spermatogenesis result in?
spermatid
what does the spermatid mature into?
the sperm
why do males never run out of sperm?
because the stem cell population keeps renewing
what are the 3 main areas of the sperm structure?
- Head
- Midpiece
- Tail
what is the head structure of the sperm?
Contains haploid nucleus → DNA
Tip → acrosome → golgi derived structure which is important for fertilisation → contain digestive enzymes
what is the midpiece structure of the sperm?
Energy is provided by lots of mitochondria
Used for the swimming movement of the sperm
what is the tail structure of the sperm?
- Contains a structure known as an axoneme → consists of microtubules that can slide against each → when they slide this causes the bending of the tail which means the sperm can swim
- This sliding of microtubules requires energy
what is the function of female reproductive system?
production of eggs and support the developing embryo
where are eggs produced?
ovaries
where are the eggs released to from the ovaries?
move through the oviduct into the uterus
what happens to the egg if there is no fertilisation?
leave via the vagina
what happens to the egg if there is fertilisation?
- occurs inside the oviduct
- sperm has to travel to find the egg
what is the start of the production of eggs?
- primordial germ cell in the embryo
- give rise to the oogonium in the embryo
- self renew for a while
when in the production of eggs do they stop self renewing?
- in the embryo
- give rise to a finite number of primary oocyte
what happens to the primary oocyte?
starts the first meiotic division - arrest in prophase
what happens in puberty in the production of eggs?
- only one primary oocyte a month completes division to for a secondary oocyte and a polar body
- secondary oocyte much bigger than the polar body
what happens to the polar body?
degrades
what happens to the secondary oocyte?
- contians most of the material present in the cytoplasm
- continues development
- goes through a second meiotic division
- arrests again
- only completed during fertilisation
describe the interaction between oocytes and follicle cells in the ovaries?
- oocytes surrounded by follicle cells
- oocytes with follicle cells are known as the follicle
- find several follicles in different stages of maturations
- oocytes are released and follicle cells stay behind
- forms a structure known as the corpus luteum
what is the structure of an oocyte?
- can see the polar body
- surrounded by a glycoprotein layer
- some follicle cells are released with the oocyte
what is the zona pellucida?
glycoprotein layer.
what is the role of zona pellucida?
important for sperm-egg recognition and stops more than one sperm fertilising an egg
what is the corona radiata?
follicle cells that are released with the oocyte
what is function of the corona radita?
send nutrients to the oocyte → when released its important to attract sperm to the oocyte → produces chemo attract that tell the sperm where to swim too
how are gametes contorlled?
by hormones released from the hypothalamus and anterior pituitary gland
what hormones does the hypothalamus release?
releases GnRH (gonadotropin-releasing hormone)
what does GnRH stimulate?
FSH and LH to be released from the anterior pituitary gland
what is FSH?
follicle stimulating hormone
what is LH?
luteinizing hormone
what type of hormones are FSH and LH?
gonadotropins - they act on the gonads
how is sperm production stimulated?
stimulated by Sertoli cells in response to testosterone and FSH
describe the hormonal control in the release of a sperm in the male reproductive system
- GnRH - blood stream - pituitary gland
- Release of FSH and LH
- LH acts on leydig cells
- Leydig cells produce testosterone
- testosterone and FSH act on sertoli cells
- promotes spermatogenesis
where are leydig cells found?
in between the seminiferous tubules
other than promoting spermatogenesis what other role does testosterone have?
- affects production of LH and FSH
- acts on the anterior pituitary gland
- inhibits LH and FSH aswell as GnRH
- negative feeedback loop
why is hormone control of the female reproductive system more complicated?
due to the mestrual cycle
what are the 2 phases of the menstrual cycle?
- Follicular phase
2. Luteal phase
Describe the hormonal control of the female reproductive system.
- start = low levels of LH and FSH
- follices mature, release increasing amounts of estradiol
- high levels = stimulates LH and FSH
- LH surge causes ovulation
- follicle cells that remain in the ovary secrete progesterone
- high levels of estradiol causes the uterine lining to thicken
- high levels of progestoerone maintain the thickened uterine lining
- if it drops the corpus luteum and therefore uterus lining degrades
what is estradiol?
an oestrogen
what affect does low levels of oestrogen have on FSH and LH?
negative effect on production
how is the uteruls lining maintained during fertilisation?
corpus luteum is maintain and prevented from degrading
how is the corpus luteum prevented from degrading?
- hCG → human chorionic gonadotropin
- Produced after fertilisation by the developing embryo to maintain the corpus luteum so progesterone is produced
- Later on in pregnancy the placenta takes over
how does the oocyte move along the oviduct?
muscle contraction and cilia
how does the sperm reach the oviduct?
mediated by contractions of the female reproductive syste,
what is capacitation?
- substance present in the female reproductive tract change the sperm
- change composition of the proteins present on the surface
- activates it - more motile
- sperm can only fertilise after capacitation
what happens to the sperm when it reaches the oviduct?
has to start actively swimming
what are the 2 mechanism that attract sperm?
- Chemotaxis
2. Thermotaxis
what is chemotaxis?
- Cells that surround the egg release chemoattractant
- Sperm detects these and swims towards them
- Main attractant is progesterone
what is thermotaxis?
- This part of the body is slightly warmer
- Sperm can sense the temperature gradient and swim towards that part of the body
what happens when the sperm reaches the egg?
needs to penetrate the outer layers so the sperm and egg can fuse
what is the first layer of the oocyte and how does the sperm get through?
- barrier of follicle cells
- releases digestive enzymes
how does the sperm move through the 2 outer layers?
releases hydrolytic enzymes from acrosomes - needs to move through the zona pellucida
what happens when the sperm meets the membrane of the oocyte?
- fuses
- causes the oocyte to complete meiosis II
- blocks the entrance of other sperm
how does the oocyte block the entry of another sperm?
fusion triggers the release of substances found in vesicles → content is exocytosed to the outside and change the zona pellucida so other sperm cannot go through
What are the stages of human development?
- Cleavage stage
- Compaction
- Blastocyst formation
- Gastrulation
- Oranogenesis
- Organs formed
what is the cleavage stage?
set of cell divisions that occur is not associated with an overall growth of the embryo → with each division the cells become smaller and smaller (become multicellular)
what is the compaction stage?
around the 16 cell stage → surface appears much more smooth → start to express more cell adhesion molecules → bind more tightly to each other
what is the blastocyst formation?
- fluid filled cavity at the centre of the embryo
- 2 different cell types
- embryo implants into the uterine lining
- has to hatch from the zona pellucida
what are the 2 different cell types in the blastocyst?
- inner cell mass
- trophoblast cells
what is the inner cell mass?
give rise to all the tissues of the developing embryo
what are trophoblast cells?
form part of the placenta → secrete enzymes that can digest a hole in the zona pellucida and so it can hatch out
what is gastrulation?
- inner cell mass differentiates into epiblast and hypoblast
- cavity forms on top of the cell layers
- all 3 germ layers are formed
- cells move underneath epiblast to form the different layers
what is the epiblast
give rise to all tissues
what is the hypoblast
transient structure
what are the 3 germ layers?
ectoderm. mesoderm. endoderm
what is organogenesis?
- 3 germ layers give rise to all the organs of the developing embryo
- occurs from around week 3-week 8
what does the ectoderm give rise to?
outer layers of the skin, nervous system, posterior pituitary gland, cornea and lens of the eye
what does the mesoderm give rise to?
muscle, bone, connective tissue, circulatory system, kidneys, gonads
what does the endoderm give rise to?
lining of the respiratory tract, lining of the digestive tract, liver, gallbladder, pancreas, thyroid gland
what is preimplantation development?
Embryo moves along the oviduct mediated by muscle contraction and cilia
In the uterus the blastocyst hatches and implants into the uterus lining
