APS136 1 Flashcards
Sex is not the same as…
reproduction
Reproduction is…
the production of offspring (either sexual or asexual)
Sex is…
the fusion of genetic material from two different parents during reproduction
A higher rate of reproduction can be achieved by reproducing …
asexually (cloning)
What are the advantages of asexual reproduction?
More efficient, easier, cheaper, relatively error-free
What are the disadvantages of asexual reproduction?
Any mutations also transmitted
What is fragmentation?
Parent body broken into pieces which then develop into adults - followed by regeneration (regrowth of lost body parts)
What is binary fission?
Single cell divides into 2 individual daughter cells
What is budding?
Offspring grows out of body of parent (specialised masses of cells released from parent that can develop into offspring)
What is parthenogenesis?
Virgin birth - unfertilised eggs develop into offspring but are not haploid (doesn’t occur in mammals due to genomic imprinting)
Parthenogenesis does not occur in mammals due to…
Genetic imprinting
What are the 4 main types of asexual reproduction?
Binary fission, fragmentation, budding, parthenogenesis
Some species reproduce both sexually and asexually, depending on…
environmental factors and stresses.
Low stress = asexual
High stress = sexual
e.g. aphids
Sexual reproduction has existed for…
1.5-2 billion years (life ~3.8bn)
Sexual reproduction involves…
meiosis, leading to recombination and segregation
recombination can … deleterious mutations and bring together … genetic combinations
Remove, novel
What are the 3 fundamental processes required for sexual reproduction?
- Gametogenesis - production of gametes
- Mating - transfer of gametes
- Fertilisation - fusion of gametes
Mating can be…
internal or external
requires males and females to synchronise
Broadcast spawning is an example of…
external fertilisation
What is required for external fertilisation?
Water - otherwise gametes would dry out
What are the problems with external fertilisation?
Can’t control delivery, requires huge numbers of gametes, predation of eggs is likely
internal fertilisation can be..
direct or indirect
What is direct internal fertilisation?
Sperm transferred directly into a female, often by an intromittent organ
What is indirect internal fertilisation?
Male deposits sperm ‘packet’ (spermatophore) and female picks it up
e.g. springtails
Hermaphrodites are individuals with…
both male and female reproductive parts - exchange sperm and use to fertilise own eggs
+ generally not self-fertilising
What are the 2 stages of gametogenesis?
- Meiosis - converting diploid cells into haploid cells
2. Spermatogenesis and oogenesis
Sperm are produced in the…
Seminiferous tubules (in the testes)
What transfers sperm to the penis?
Vas deferens
Where is sperm stored?
Epididymis
How much of semen is seminal fluids?
90%
Sperm are produced from … … …
Spermatogonial stem cells
Primary spermatoctye (diploid) -> Secodary spermatocytes (diploid) -> spermatids (haploid) -> sperm (haploid)
Each primary spermatocyte gives rise to … sperm cells
4
In drosophila spermatogenesis occurs in..
cysts within the testes
- from distal to proximal
- starts in larval stage
- sperm produced in a few days
In humans spermatogenesis occurs in..
seminiferous tubules within testes
- from periphery to lumen
- starts in puberty
- sperm produced in approx. 74 days
In oogenesis, the primary oocyte undergoes meiosis 1 to form…
A secondary oocyte (diploid) and the first polar body, which contains far less cytoplasm
In oogenesis, meiosis 2 forms…
2 more polar bodies (so 1 haploid ovum and 3 haploid polar bodies)
Polar bodies…
are never fertilised - not enough resources
At puberty, the hypothalamus secretes..
gonadotrophin-releasing hormone (GnRH)
GnRH stimulates..
FSH (follicle stimulating hormone) and LH (lutenizing hormone) from the anterior pituitary cells.
In spermatogenesis, FSH…
LH…
- Stimulates development of seminiferous tubules (where sperm form) and spermatogenesis acting together with testosterone by stimulating Sertoli cells
- Stimulates Leydig cells to secrete testosterone which stimulates spermatogenesis
In oogenesis, FSH…
LH…
- Stimulates development of follicles and secretion of estrogens
- Stimulates maturation of follicles and release of ova at ovulation
Estrogen…
enhances growth of follicles, grows endometrium
Progesterone…
grows and maintains endometrium for pregnancy, secretes nutrients for embryo
corpus luteum…
hormone secreting after ovulation
Fertilisation is…
the union of (haploid) sperm and ovum (to produce a diploid zygote)
What are the barriers faced during fertilisation?
- Sperm must make it to the ovum
- Gametes must recognise each other
- Sperm must penetrate ovum
- Haploid egg nucleus and sperm nucleus must fuse to form diploid zygote (syngamy)
- Ovum must block entry of additional sperm (polyspermy) to avoid polyploidy
What proportion of sperm survive to reach the ovum?
less than 1 in a million
What are the features of a mammalian egg?
- Germinal vesicle: nucleus containing DNA (nucleolus = germinal spot)
- Ooplasm: cytoplasm containing nutrients
- Vitelline membrane: Cell membrane surrounding ooplasm
- Zona Pellucida: extracellular matrix containing glycoproteins
Corona radiata: layer of follicle cells
What are the main sections of a mammalian sperm cell?
- Head: contains nucleus with sperm DNA, capped with acrosome, which penetrates the egg membrane using enzymes
- Neck: contains the centriole (important for tail formation and movement, and development of embryo after fertilisation)
- Midpiece (with central filamentous core): contains the mitochondria which provide energy for movement
- Tail: drives the sperm forward
Sperm can only move through…
liquid - terrestrial animals overcome this using seminal fluid (and oviductal fluid in female reproductive tract)
External fertilisation almost always occur in … environments
aquatic
Fertilisation requires sperm … of the egg coat
penetration
In mammals, sperm penetrate the cumulus cell layer via … …, and sperm undergoes … reaction to penetrate the zona pellucida. Sperm and … plasma membranes … (mediated by sperm-egg recognition/attachment proteins). The sperm … (and certain other sperm components) enter the ovum. Membrane and ZP block to … is rapidly initiated.
hyperactivated motility, acrosome, oocyte, fuse, nucleus, polyspermy
Polyspermy is … to mammals
pathological (and fatal)
In sea urchins, eggs have a …
protective jelly coat
- contains proteins with strong, species-specific chemoattractant properties
Under the sea urchin egg’s jelly coat is the egg plasma membrane, which is lined with … that hold … receptors. As the sperm release their acrosomal enzymes, a … develops from the sperm head (known as the … …), which reaches out to contact the egg’s surface. On the surface of the protrusion is a species-specific protein called …, which is detected by the ovum’s protein receptors. This is a highly effective barrier to interspecific fertilisation.
microvilli, protein, protrusion, acrosomal process, bindin
In sea urchins, once membrane fusion has occured, the … … of the plasma membrane changes to prevent other sperm from fusing with the egg - different to in mammals (where … … change)
electrical potential, material properties
Human egg coat protein … is in the top 5% most divergent molecules between humans and rodents, displaying the … diversification of reproductive molecules, particularly those involved in sperm-egg recognition.
ZP2, rapid
…, found in abalone gastropods, is one of the fastest evolving metazoan proteins known, and is a sperm protein involved in…
Lysin, dissolving the egg envelope
When it is about to be laid, the egg of a kiwi takes up around…
3/4 of the female’s body
Across bird species, on average … of eggs fail to hatch
10-15%
In kakapos, egg hatching failure rates can be over …
70%
- a reason as to why they are so endangered
Why do eggs fail?
Fertilisation failure
- failure of sperm to reach the egg
- sperm or ovum dysfunction (may be linked to poor male/female quality)
- Female anti-sperm response
Embryo death
- Male factors (e.g. genetic)
- Female factors
- Male-female incompatibility (e.g. from inbreeding)
- External factors
What is the most intense site of selection for sperm?
The vagina - 0.0001% of sperm that enter get further than the vagina
What are the characteristics of successful sperm?
- motility is crucial (speed and direction)
Once the sperm have got past the vagina…
muscular contraction actually help the sperm to reach the egg (even dead sperm reach the infundibulum when put past the vagina)
What determines sperm motility?
- morphology (long sperm have competitive advantage as they swim faster - long sperm males have higher paternity than short sperm males
In birds, polyspermy is…
normal
In birds, embryo survival is much higher…
if there is lots of sperm present in the egg (high polyspermy)
- supernumerary sperm
- potentially to help with ion transfer in such large eggs
