Sex and reproduction Flashcards
The popularity of sex sex, disease and mammalian sex determination mammalian sex determination and the indifferent gonad, human reproductive systems mammalian development genetic and cellular principles
asexual reproduction is common in what type of plants
angiosperms
asexual reproduction in plants is typically an extension of the capacity for …………………………….
intermediate growth
plant growth can be sustained or renewed indefinitely by what
meristems
what are meristems
regions of undifferentiated dividing cells
what are parenchyma cells
plant cells that can divide and differentiate into more specialised types of cells, enabling plants to regenerate lost parts
give an example of hoe a detached root or stem fragment can develop into whole new offspring
pieces of potato with a bud can generate a whole new plant
what is fragmentation
separation of a parent plant into parts that develop into whole plants by regeneration (one of the most common modes of asexual reproduction)
what is apomixis
produce seeds without pollination or fertilization by a male gamete
- a diploid egg in the ovule gives rise to an embryo and the ovules mature into sees
what are advantages of asexual reproduction
- no need for a pollinator
- allows a plant to pass all its genetic material onto its progeny
- if the plant is well suited to its environment asexual reproduction is ideal because it doesn’t introduce any variation - good in a stable environment
what is asexual plant reproduction know as
vegetative reproduction
what are disadvantages of asexual reproduction
- doesn’t produce any variation
- uniformity puts populations at risk of local extinction if there were to be a catastrophic environmental change
what are the advantages of sexual reproduction
- introduces variation so advantageous in unstable environments
- sexually produced seeds allow more widespread dispersal of offspring
- seed dormancy allows growth to be suspended until the environmental conditions become more favourable
what are the disadvantages of sexual reproduction
- requires a lot of resources and energy
are seeds produced in asexual reproduction
asexual reproduction new plants are obtained without production of seeds or spores
new plants are produced form roots, stems, leaves and buds
what is selfing
when plants self fertilize (sexual reproduction)
what is asexual reproduction
generation of offspring from a single parent that occurs without the fusion of gametes - in most cases offspring are genetically identical to the parent
what is sexual reproduction
reproduction rising from the fusion of 2 haploid gametes making a diploid zygote
what is parthenogenesis
a form of asexual reproduction in which females produce offspring from unfertilised eggs (offspring can be either haploid or diploid)
what is a hermaphrodite
an individual that functions as both a male and female in sexual reproduction by producing booth sperm and eggs (common in sessile animals)
this way any 2 individuals can mate or some can even self fertilize
what can prevent plants from self fertilizing and why does this happen
- some plants lack carpels or stamens
- some plants’ carpels and stamens mature at different times
- carpel and stamens may be structurally arranged in a way that an animal pollinator is unlikely to transfer pollen from the anther to the stigma of the same flower
- self incompatibility -plant rejects its own pollen
this all contributes to genetic variety by ensuring that sperm and egg come from different plants
what is fission
splitting and separation of a parent organisms into 2 individuals of approximately equal size
what is budding
when new individuals arise from outgrowths of existing ones
what is parthenogenesis thought to be a response to
low population density
what is sex reversal
changing sex e.g. when the one male of wrasse dies the largest female turns into a male - producing sperm instead of eggs
e.g. oyster change from male to female when they are at their greatest size to increase reproductive success as they can store more eggs
cycles in reproductive activity are often related to what
changing seasons - cycles are regulated by hormones which are in turn regulated by environmental cues
why do animals have reproductive cycles
it allows them to conserve resources, reproducing only when sufficient energy sources are available and when environmental conditions favour the survival of the offspring
when in a reproductive cycle does ovulation occur
the midpoint
how can climate change decrease reproductive success
seasonal temperature is an important cue for reproduction so any fluctuations could confuse the cycle and make it less successful
what are the 2 types of eggs that a female daphnia can produce
- an egg that requires fertilization in order to develop
2. an egg that develops by parthenogenesis
when do daphnia reproduce asexually
when environmental conditions are favourable
when do daphnia reproduce sexually
when they are under environmental stress - the change from sexual to asexual is roughly linked with season
how do lizards still use sexual courtship even though they are all female
one female of each mating pair mimics a male and they switch roles several times
they take on the male role when levels of progesterone are high
they take on the female role when oestradiol levels are high
a female is more likely to ovulate when she is mounted at a critical point of the hormone cycle
these parthenogenic lizards evolved from species having 2 sexes and this is why they still require sexual stimuli
why is sexual reproduction maintained when asexual reproduction produces more offspring
- in sexual reproduction the offspring show variation and offspring are more likely to survive environmental change
- beneficial gene combinations might speed up adaptation
- shuffling genes might allow a population to rid itself of harmful genes more readily
what is external fertilization
when the female releases eggs into the environment where the male then fertilises them
what is internal fertilization
sperm is deposited in or near the female reproductive tract fertilize eggs within the tract
what is spawning
when several females release their eggs at the same time in aquatic environments
if the release of gametes is not synchronised between individuals that fertilize externally then what can occur to ensure they release gametes at the same time
courtship behaviours
what are pheromones
small volatile water soluble molecules released by an organism that can influence the physiology and behaviour of other individuals of the same species
they may function as mate attractants
sexual reproduction relies on sets of cells that are …….… for eggs and sperm
precursors
what are gonads
organs that produce gametes
in many insect species the female reproductive system includes one or more spermathecae, what are these
sacs in which sperm may be kept alive for extended periods - the female releases the sperm in response to stimuli which allows offspring to be produced when conditions are well suited to survival
what is a cloaca
a common opening for the digestive, urinary, and reproductive tracts found in many non mammalian vertebrates but in few mammals - males can turn the cloaca inside out to release sperm if they lack a well developed penis
what is monogamy
sustained sexual partnership of 2 individuals
how can monogamy be sustained in some species
in fruit flies both the males and females can influence their partners mating success
males can diminish the chance of a female mating successfully with another partner
at what age do the anatomical signs of sex begin to emerge in an embryo
2 months
what is the SRY gene
the sex determining region of Y
- In the presence of the gene the gonads develop into testes
- in the absence of the gene the gonads develop into ovaries
what is a sex linked gene
a gene located on a sex chromosome
what are genes located on the X and Y chromosomes called
X linked genes and Y linked genes respectively
why are very few disorders transferred from father to son on the Y chromosome
because there are few Y linked genes
for the development of female gonads which gene is required
WNT4 found on chromosome 1
what does the gene WNT4 encode for
a protein that promotes ovary development
what happens if an XY embryo has extra copies of WNT4
it can develop rudimentary female gonads
which sex chromosome has more genes that are not related to sex
X
if an X linked trait is due to a recessive allele, a female will only express the phenotype if she is ……………. for the allele
homozygous
are males or females more likely to show an X linked recessive disease phenotype
explain
males are more likely to be affected because they only have one X chromosome so there is nothing to mask the recessive allele and so it will always be expressed
females have 2 X chromosome meaning that if they only inherit one copy of the recessive allele it will be masked by the other X chromosome and they will not express the diseased phenotype
what is meant by viruses being obligate intracellular parasites
they can replicate only within a host cell
what is the host range of a virus
the number of host species it can infect
how do viruses usually identify host cells
by a lock and key fit between viral surface proteins and specific receptor molecules on the outside of cells
when does a viral infection begin
when a virus binds to a host cell and the viral genome makes its way inside
how can the viral genome make its way into the host cell
- it can be injected by T phages using their tail apparatus
- viruses may be taken up by endocytosis, enveloped viruses may be taken up by fusion of the viral envelope with the host’s plasma membrane
how does entry of the viral genome into the host cell affect the host cell
the proteins encoded by the viral genome reprogram the cell to copy the viral genome and manufacture viral proteins
what resources do host cells supply for the virus
nucleotides enzymes ribosomes tRNAs amino acids ATP DNA polymerase etc
how do viruses replicate their genome and make new genomes
replicate - they use virally encoded RNA polymerase that can use RNA as a template
new genomes - use host cell DNA pol to synthesise new genomes along the templates provided by the viral DNA
what are the 4 steps in the replicative cycle of a virus
- virus enters the cell and is uncoated releasing viral DNA and capsid into the cell
- host enzymes replicate the viral genome
- host enzymes transcribe and translate viral DNA to make more capsid proteins
- viral genomes and capsid proteins self assemble into new virus particles which exit the cell
what are plasmids
small circular DNA molecules that replicate independently of the bacterial chromosome and are occasionally transferred between cells
what are transposons
DNA segments that move from one location to another in a cells genome
what are emerging viruses
viruses that suddenly become apparent e.g. HIV, ebola, zika and the west nile virus
what is virulence
the degree of damage caused by a pathogen to its host
why do RNA viruses have a high mutation rate
they do not have a proofreading system - RNA pol does not check or correct errors in replication
what are the human males external and internal reproductive organs
external - scrotum and penis
internal:
- goads that produce sperm and reproductive hormone
- accessory glands that secrete products for sperm movement
- ducts that carry sperm and glandular secretions
what are the male gonads
the testes
testes produce sperm in highly coiled tubes called …….………
seminiferous tubules
most mammals produce sperm properly only when the testes are warmer/cooler than the rest of the body and what maintains this temperature
cooler - why they hang outside the body
testes temperature is maintained by the scrotum (a fold of the body wall)
where do the testes develop and what happens to them at birth
they develop in the abdominal cavity and then descend into the scrotum just before birth
what is a testis within a scrotum called
a testicle
why are some mammals able to keep their testes within the abdominal cavity at all times
because their body temperature is low enough to allow sperm maturation
between breeding seasons the testes of some rodents are drawn back into the …………………, interrupting sperm maturation
abdominal cavity
where does the sperm pass from the seminiferous tubules to and what happens to the sperm during this journey from the seminiferous tubules
they travel to the coiled duct of an epididymis which take about 3 weeks and during this time the sperm complete maturation and become motile
what happens to the sperm during ejaculation
the sperm are propelled from each epididymis through a muscular duct called the vas deferens
how many vas deferens does a male have
2 - one from each epididymis
how are the vas deferens arranged in the body
each one extends around and behind the urinary bladder where it joins a duct from the seminal vesicle, forming a short ejaculatory duct
the ejaculatory ducts open into the ………….
urethra
what is the urethra
the outlet tube of both the excretory and the reproductive system (it runs through the penis and opens to the outside at the tip of the penis)
what are the 3 sets of accessory glands in the male reproductive system
seminal vesicles
prostate gland
bulbourethral glands
what is the role of the accessory glands
they produce secretions that combine with sperm to form semen - the fluid that is ejaculated
two ……………… contribute about 60% of the volume of semen
seminal vesicles
describe the fluid secreted from the seminal vesicles
thick, yellowish and alkaline
it contains mucous, fructose, a coagulating enzyme, ascorbic acid and local regulators called prostaglandins
what is the role of the fructose in the secretions from the seminal vesicles
it provides most of the sperms energy
where does the prostate gland secrete its product
directly into the urethra through small ducts
describe the fluid secreted from the prostate gland
thin and milky
contains anticoagulant enzymes and citrate (sperm nutrient)
where are the bulbourethral glands found
they are found along the urethra below the prostate
what is the role of the bulbourethral glands
before ejaculation they secrete clear mucous that neutralises any acidic urine remaining in the urethra
what is the evidence that correlates with the high failure rate of the withdrawal method
the bulbourethral fluid carries some sperm released before ejaculation
where is the prostate gland located
beneath the bladder
where is the seminal vesicle located
behind the bladder
what does the penis contain
3 cylinders of spongy erectile tissue and the urethra
what happens too the erectile tissue during sexual arousal
- the erectile tissue fills with blood from the arteries
- increasing pressure seals off the veins that drain the penis causing it to engorge with blood
- the resulting erection enables the penis to be inserted into the vagina
what can cause erectile dysfunction
alcohol consumption
some drugs
emotional issues
ageing
what do drugs like Viagra do
- they promote the vasodilating action of the local regulator Nitric Oxide
- the smooth muscle in the blood vessels of the penis relax enhancing blood flow into the erectile tissues
this allows those with long term erectile dysfunction to achieve an erection
what is the baculum
the bone in some mammal penises that further stiffens the penis for mating
what is the glans of the penis
the head
what is the glans surrounded by
a fold of skin called the prepuce (foreskin)
what are a human females external reproductive structures
the clitoris and two sets of labia
what are the human females internal reproductive structures
- gonads which produce eggs and reproductive hormones
- a system of ducts and chambers which receive and carry gametes and house the embryo and fetus
what are the female gonads
a pair of ovaries that flanks the uterus and are held in place in the abdominal cavity by ligaments
what is the outer layer of the ovaries packed with
follicles - each consisting of an oocyte (a partially developed egg) surrounded by support cells which nourish and protect the oocyte
what is the oviduct and where is it located
it is the fallopian
it extends from the uterus toward an opening at each ovary
what is the role of cilia that line the oviduct
upon ovulation the cilia of the epithelium lining of the oviduct help collect the egg by drawing fluid from the body cavity into the oviduct
oviduct contractions and the cilia convey the egg down the oviduct to the uterus (womb)
what is the uterus
also known as the womb
it is a thick muscular organ that can expand during pregnancy
what is the inner lining of the uterus called
the endometrium
what is the neck of the uterus called
the cervix - it opens into the vagina
what is the outside opening of the vagina
the vulva
what encloses and protects the vulva
the labia majora
the vaginal opening and the urethra are located in a cavity bordered by what
the labia minora
what is the clitoris
it is found at the top of the labia minora and consists of erectile tissue supporting a rounded glans covered by the prepuce
during sexual arousal what happens the labia minora, clitoris and vagina
they enlarge due to engorging blood
during sexual arousal what do the vestibular glands do
they secrete lubricating mucous that facilitates intercourse
what are mammary glands
they are present in both sexes
they produce milk in females
small sacs of epithelial tissue in the glands secrete milk
the milk then drains into a series of ducts that open at the nipple
what do the breasts contain in addition to the mammary glands
adipose tissue
what is gametogenesis
the production of gametes
what is spermatogenesis
the formation and development of sperm
what is oogenesis
the development of mature eggs
where does cell division and maturation occur
in the seminiferous tubules coiled in the 2 testes
in what 3 ways do spermatogenesis and oogenesis differ
- only in spermatogenesis do all 4 products of meiosis develop into mature gametes. (in oogenesis cytokinesis during meiosis is unequal with almost all the cytoplasm segregated to single daughter cell. The large cell is destined to become the egg and the smaller cells (polar bodies) become degenerate
- spermatogenesis occurs throughout adolescence and adulthood (mitotic divisions in oogenesis are complete before birth and production of mature gametes ceases at about 50)
- spermatogenesis produces mature sperm from precursor cells in a continuous sequence (in oogenesis there are long interruptions)
where are stem cells (spermatogonial stem cells) that give rise to sperm found
near the outer edge of the seminiferous tubules
how do the spermatogonial stem cells arise
from division and differentiation of primordial germ cells in the embryonic testes
in mature testes upon mitosis what doo spermatogonial cells produce
spermatogonia
upon mitosis what do spermatogonia generate
primary spermatocytes
each primary spermatocyte gives rise to …….. spermatids through meiosis
4
describe the structure of sperm
a head containing a nucleus which is tipped with the acrosome which contains enzymes that help sperm penetrate the egg
the sperm have a flagella tail powered by ATP for movement
go through the spermatogenesis process
primordial germ cell in embryo MITOSIS spermaogonial stem cell MITOSIS spermatogonium MITOSIS primary spermatocyte MEIOSIS I secondary spermatocyte MEIOSIS II early spermatid DIFFERENTIATION sperm cell
oogenesis begins in the female embryo with the production of …………….. from primordial germs cells by mitosis
oogonia
the oogonia undergo mitosis to form what
primary oocyte
what happens to the primary oocyte
embryo - it undergoes meiosis but is arrested at prophase I
puberty - meiosis I is completed and meiosis II is carried out and arrested at metaphase II. this produces a polar body (which may or may not divide again) and a secondary oocyte
what does FSH stand for
follicle stimulating hormone
what does FSH do in females
beginning at puberty it stimulates a small number of follicles to resume growth and development
how many follicles fully mature each month
one with its primary oocyte completing meiosis I
what happens when a follicle fully matures
its primary oocyte completes meiosis I and the second meiotic divisions begin but stop at metaphase
the secondary oocyte is released at ovulation when its follicle breaks open
under what circumstances does meiosis II resume in the secondary oocyte
only if it is penetrated by a sperm
what is the functional product of complete oogenesis
a single mature egg containing a sperm head
what is the exact definition of fertilization
the fusion of the haploid nuclei of the sperm and secondary oocyte
what does the ruptured follicle left behind after ovulation develop into
the corpus luteum
what does the corpus luteum do
it secretes oestradiol and progesterone (hormone that helps maintain the uterine lining during pregnancy
if the egg isn’t fertilised the corpus luteum degenerates
mammalian reproduction id governed by the coordinated actions of hormones from which 3 places
hypothalamus
anterior pituitary
gonads
endocrine control begins with the hypothalamus which secretes what
gonadotropin releasing hormone (GnRH)
what does GnRH do
it directs the anterior pituitary to secrete the gonadotropins follicle stimulating hormone (FSH) and luteinizing hormone (LH)
LH and FSH are tropic hormones - what does this mean
they regulate the activity of endocrine cells or glands
how do LH and FSH support gametogenesis
by stimulating sex hormone production by the gonads
what are the 3 major types of steroid sex hormones produced and secreted by the gonads
androgens - mainly testosterone
oestrogens - mainly oestradiol
progesterone
although the gonads are the major source of sex hormones, the …………………….. also secrete sex hormones in small amounts
adrenal glands
the androgens produced in male embryos direct the appearance of primary sex characteristics. what are primary sex characteristics
the structures involved directly in reproduction which include the seminal vesicles and associated ducts as well as external reproductive structures
during sexual maturation sex hormones induce the formation of …………………..
secondary sex characteristics
what are secondary sex characteristics
the physical and behavioural differences in males and females that are not directly related to the reproductive system - this often leads to sexual dimorphism
in directing spermatogenesis which cells do FSH and LH act on in the testis
FSH stimulates Sertoli cells located in the seminiferous tubules to nourish developing sperm
LH causes leydig cells, scattered in the connective tissue between the tubules, to produce testosterone and other androgens which promote spermatogenesis in the tubules
what are the two negative feedback mechanisms that control sex hormone production in males
- testosterone regulates blood levels of GnRH, FSH and LH through inhibitory effects on the hypothalamus and anterior pituitary
- inhibin (a hormone produced by Sertoli cells in males) acts on the anterior pituitary gland to reduce FSH secretion
these circuits together maintain androgen levels in the normal range
what are other roles of Leydig cells besides producing testosterone
they secrete small quantities of other hormones and local regulators, including oxytocin, renin, angiotensin, corticotropin-releasing factor, growth factors and prostaglandins
these signals coordinate the activity of reproduction with growth, metabolism, homeostasis and behaviour
what are the two closely linked reproductive cycles in females
the ovarian cycle and the uterine cycle
what is the ovarian cycle
cyclic events in the ovaries - once per cycle a follicle matures and an oocyte is released
what is the uterine cycle
changes in the uterus - a menstrual cycle
what happens in a menstrual cycle
the endometrium (lining of the uterus) thickens and develops a rich blood supply before being shed through the cervix and the vagina if pregnancy does not occur
why is it important the ovarian and uterine cycles are linked
by them being linked hormone activity synchronises ovulation with the establishment of a uterine lining that can support embryo implantation and development
what happens if an oocyte is not fertilized
the uterine lining is sloughed off and another pair of ovarian and uterine cycles begins
what is menstruation
cyclic shedding of blood rich endometrium from the uterus through the cervix and the vagina
what are the steps in the ovarian cycle
- hypothalamus secretes GnRH which stimulates the anterior pituitary to secrete small amounts of FSH and LH
- FSH stimulates follicle growth, aided by LH, and the follicles start to make oestradiol
- oestradiol concentration slowly rises during most of the follicular stage when follicles grow and oocytes mature
- when oestradiol secretion by the follicle begins to steeply rise and the FSH and LH levels increase markedly
- the maturing follicle enlarges to form a bulge at the surface of the ovary
- the follicular stage ends at ovulation about a day after the LH surge
- the luteal phase follows ovulation
- LH stimulates the remaining follicular tissue to form the corpus luteum which releases progesterone and oestradiol which exert negative feedback on the hypothalamus an the anterior pituitary
- negative feedback reduces the level of FSH and LH secretion preventing maturation of another egg when pregnancy may be under way
- if pregnancy doesn’t occur low gonadotropin (FSH and LH) levels cause the corpus luteum to disintegrate triggering a sharp decline in oestradiol and progesterone which stops the negative feedback
- the pituitary can then secrete enough FSH to stimulate the growth of new follicles, initiating the next ovarian cycle
low levels of oestradiol ………. secretion of pituitary gonadotropins (LH and FSH)
inhibits
high levels of oestradiol …………. gonadotropin (LH and FSH) secretion from the pituitary by
stimulate
how do high levels of oestradiol stimulate LH and FSH
oestradiol causes the hypothalamus to increase output of GnRH and also causes increased sensitivity of LH releasing cells to GnRH
what are the steps in the uterine cycle
- prior to ovulation, ovarian steroid hormones stimulate the uterus to prepare to support an embryo
- oestradiol signals the endometrium to thicken
- after ovulation the oestradiol and progesterone secreted by the corpus luteum stimulate further development of the uterine lining including enlargement of arteries and growth of endometrial glands
- if an embryo is not implanted in the endometrium by the end of the secretory phase the corpus luteum disintegrates
- the drop in ovarian hormone (oestradiol and progesterone) levels causes the arteries in the endometrium to constrict
- the uterine lining disintegrates and menstrual floe begins and a new set of follicles begin to grow
what is endometriosis
disorder in which some cells of the uterine lining migrate to an abdominal location that is abnormal (ectopic)
the ectopic tissue swells and breaks down during each ovarian cycle resulting in pelvic pain
what is menopause
the cessation of ovulation and menstruation
ovaries lose their responsiveness to LH and FSH resulting in a decline in oestradiol production
what is the estrous cycle
where the uterus reabsorbs the endometrium instead of releasing it in menstrual flow
what is vasocongestion
the filling of a tissue with blood
what is myotonia
increased muscle tension
what are the sexual response cycle stages
excitement
plateau
orgasm
resolution
how are the functions of FSH and LH similar in males and females
in both males and females FSH encourages the growth of cells that support and nourish gametes (follicle cells in females and Sertoli cells in males)
in both males and females LH stimulates the production of sex hormones that promote gametogenesis (oestrogens (mainly oestradiol) in females and androgens (manly testosterone) in males)
what are the 5 steps in formation of a human zygote and its early postzygotic events
- ovulation releases a secondary oocyte which enters the oviduct
- a sperm enters the oocyte; meiosis of the oocyte is completed and the nuclei of the sperm and oocyte fuse - producing a zygote
- cell division begins in the oviduct as the embryo is moved towards the uterus by peristalsis and cilia movement
- the embryo is nourished by endometrial secretions in the uterus and becomes a blastocyst
- the blastocyst implants in the endometrium
where are the Sertoli cells found in males
in the seminiferous tubules
between which 2 phases of the menstrual cycle do the concentrations of FSH and LH peak
between the proliferative phase and the secretory phase (this is also when oestradiol peaks - oestradiol causes the influx of FSH and LH) - at ovulation
in what phase of the ovarian cycle do FSH and LH peak
at the end of the follicular phase before going into the luteal phase - this crosses over with the proliferative and secretory phases of the uterine/ovarian cycle - at ovulation
what are the steps in oogenesis
primordial germ cell MITOSIS oogonium MITOSIS primary oocyte MEIOSIS I secondary oocyte OVULATION/SPERM ENTRY COMPLETION OF MEIOSIS II fertilized egg
once the sperm enters the secondary oocyte what is produced
a fertilized egg and a second polar body
where does the hypothalamus release GnRH to
the anterior pituitary
what does GnRH stimulate
secretion of LH and FSH from the pituitary
what do FSH and LH stimulate in females
follicle growth
what does the LH surge trigger in females
ovulation
what do progesterone and oestradiol promote
thickening of the endometrium
what is secreted by the corpus luteum
progesterone and oestradiol
