Chapter 49 - Reproduction Flashcards
What is the difference between sexual and asexual reproduction?
asexual reproduction creates genetically identical offspring to the single parent. sexual reproduction creates genetically different offspring where male and female gametes come together
What is another name for asexual reproduction?
clonal reproduction
What are the 3 advantages of asexual reproduction?
1) Preserves genetic uniformity – advantageous in environments that remain stable and uniform
2) No energy expended in producing gametes
3) No energy expended in finding a mate, especially in sparsely populated areas or in sessile organisms
What type of environment does asexual reproduction usually occur in?
aqueous
What are the 3 different types of asexual reproduction?
fission, budding, fragmentation, parthenogenesis
What is fission? example?
the parent separates into two or more offspring of approximately equal size (e.g., planarians)
What is budding? example?
a new individual develops while attached to the parent (specialized region) – offspring may break free from the parent, or remain attached to form a colony (e.g., Hydra)
What is fragmentation? examples?
pieces separate from the body of a parent and develop (regenerate) into new individuals (e.g., flatworms, annelids, and some echinoderms)
What is pathogenesis? how does it work? offspring haploid or diploid?
no fertilization takes place, offspring can be haploid or diploid and are genetically different than the parent as the egg is still produced by meiosis
What are the advantages and disadvantages of sexual reproduction?
advantages: genetic diversity improves survival rate in a changing environment
disadvantages: use energy to create gametes and find mates
What are the 3 ways sexual reproduction creates genetic varaibility?
genetic recombination, independent assortment, and random fusion of gametes
What is the ultimate sources of variability for both sexual and asexual reproduction?
random DNA mutations
What is the formation of male and female gametes called?
gametogenesis
What is a zygote?
fusion of haploid sperm and egg
What are germ cells? location?
where gametes are formed, located in testes and ovaries
What do mitotic division of germ cells produce?
spermatogonia and oogonia
What does spermatogenesis produce?
4 mature haploid spermatozoa (sperm)
What is the structure of sperm?
motile cells driven through a watery medium by a flagellum
What is spermatid? what occurs here?
immature sperm, cytoplasm is lost – except for mitochondria, which produce the ATP that drive the flagellum this creates mature sperm
What is an acrosome?
A specialized secretory vesicle containing enzymes and other proteins that help the sperm penetrate the egg forms a cap over the nucleus in the head of the sperm
What does oogensis produce?
one mature, haploid ovum (egg) – a large cell containing most of the cytoplasm of the parent cell and 3 nonfunctional polar bodies
What stage does the oocytes in the ovary remain in?
1st prophase in meiosis
What stage are the oocytes in during ovulation?
2nd metaphase
When do oocytes complete meiosis?
fertilization
What type of nutrients does the egg store for different animals?
mammal eggs contain little nutrients. Eggs of birds and reptiles contain all nutrients required for complete embryonic development
What is the purpose of the egg coat?
protect the egg from injury and infection and, in some species, protect the embryo after fertilization
How does external fertilization occur? what type of animals?
Males and females synchronize release of large quantities of eggs and sperm into the surrounding water. occurs in most aquatic invertebrates, bony fishes, and amphibians
How does internal fertilization occur? what type of animals?
Sperm are released close to or inside the entrance of the female’s reproductive tract. Internal fertilization provides the aquatic medium required for fertilization inside the female’s body. Occurs in reptiles, birds, mammals annelids, and some arthropods, mollusks, and fishes
What happens a sperm touches the outer surface of an egg?
receptor proteins in the sperm plasma membrane bind the sperm to the vitelline coat or zona pellucida
Are sperm from any species allowed to bind to any egg?
mostly no, only a sperm from the same species as the egg can recognize and bind to the egg surface
What is the acrosomal reaction? when does this happen?
Attachment of sperm to egg triggers the acrosomal reaction – enzymes in the acrosome are released from the sperm and digest a path through the egg coats
The sperm follows the path until its plasma membrane touches and fuses with the plasma membrane of the egg
What is the fast block to polyspermy? how fast does this occur? what animals does this occur?
Fusion of egg and sperm opens ion channels in the plasma membrane of the egg, spreading a wave of electrical depolarization over the egg surface
Depolarization alters the egg plasma membrane’s potential from negative to positive so that it cannot fuse with any additional sperm – eliminating the possibility that more than one set of paternal chromosomes enters the egg
occurs within a few seconds after fertilization, invertebrates
What is the slow block to polyspermy? how fast does this occur?
- Fusion of egg and sperm triggers release of Ca2+ ions from the egg’s ER into the cytosol
- Ca2+ ions activate control proteins and enzymes that initiate intense metabolic activity in the fertilized egg
- Ca2+ ions trigger the cortical reaction – cortical granules under the egg’s plasma membrane release their contents by exocytosis
- Enzymes released from cortical granules alter the egg coats so no further sperm can penetrate to the egg
occurs within minutes after fertilization
What happens when the sperm nucleus enters the egg cytoplasm?
microtubules move the sperm and egg nuclei together in the egg cytoplasm and they fuse
What is oviaparous?
animals lay eggs that contain nutrients needed for development of the embryo outside the mother’s body
What is ovoviviparous?
animals retain fertilized eggs within the body and the embryo develops in the egg – there is no uterus – eggs hatch inside the mother and offspring are released
What is vivparous?
animals retain the embryo within the mother’s uterus and nourish it during at least early development
What are eutherians?
placental mammals
What are metatherians? how does this work?
marsupials, provide nutrients to the embryo during early stages of development via an attached membranous sac containing yolk – the embryo is born at an early stage and crawls to an abdominal pouch (marsupium) where it attaches to a nipple and continues development
What is hermaphroditism?
both mature egg producing and mature sperm producing tissues are present in the same individual
Does most hermaphroditic animals fertilizes themselves? what mechanisms does they use?
no, self fertilization is prevented by anatomical barriers, or by producing mature egg and sperm at different times
What is the difference between Simultaneous hermaphrodites and sequential hermaphrodites
Simultaneous hermaphrodites develop functional ovaries and testes at the same time – sequential hermaphrodites change from one sex to the other
Where are eggs fertilized? where do they implant?
Eggs are fertilized in the oviduct and implant in the uterus lining (endometrium)
What is the greater vestibular glands?
secrete lubricating fluid in human females
What type of control is the female reproduction system under? what are the main organs? (4)
neuroendocrine control
main organs: hypothalamus, pituitary, ovaries, and uterus
What is the average ovarian cycle length?
28 days
What happens in the first part of the ovarian cycle?
increase in gonadotropin- releasing hormone (GnRH) released by the hypothalamus. GnRH stimulates the pituitary to release follicle-stimulating hormone (FSH) and luteinizing hormone (LH)
How many primary oocytes does FSH stimulate to be released from prophase of meiosis I and continue meiosis?
6 to 20
When do secondary oocytes occur?
when primary oocytes arrest in metaphase II
What forms a follicle?
secondary oocyte surrounded by cells
How does the follicle develop?
As the follicle enlarges, FSH and LH interact to stimulate the follicular cells to secrete estrogens, primarily estradiol
What effects do estrogens have?
Secreted in low amounts, estrogens have a negative feedback effect on the pituitary, inhibiting its secretion of FSH
High estrogen level has a positive feedback effect on the hypothalamus and pituitary, increasing release of GnRH and stimulating the pituitary to release a burst of FSH and LH
How do the levels of estrogen change over the ovarian cycle?
Estrogen secretion increases steadily, and its level peaks at about 12 days after follicle development begins
What hormones influence ovualtion?
The burst in LH secretion stimulates follicle cells to release enzymes that digest the wall of the follicle, causing it to burst and release the egg (ovulation)
How many oocytes does each ovary contain at birth? stage of development?
around 1 million, arrested at the end of the first meiotic prophase
How many oocytes survive till female is sexually mature?
200,000 - 400,000
How many oocytes are ovulated in a female’s lifetime?
400
How do eggs travel after ovulation?
The egg is pulled into the oviduct by the current produced by the beating of cilia lining the oviduct
What is the luteal phase and what hormones are involved?
last stage of menstrual cycle initiated by LH
What is the corpus luteum?
LH causes the follicle cells remaining at the surface of the ovary to grow into a corpus luteum, which secretes estrogens, large quantities of progesterone, and inhibin
If fertilization does not occur, the corpus luteum gradually degenerates and its cells are phagocytized – in the absence of progesterone, menstruation begins
What does progesterone do?
stimulates growth of the uterine lining and inhibits contractions of the uterus – it also inhibits secretion of GnRH, which inhibits release of FSH and LH
What is menstrual flow the result of? length? hormones involved?
Menstrual flow results from the breakdown of the thickened endometrium – when flow ceases (day 4 5 of the cycle)
progesterone stops blood supply
When does the endometrium begin to grow again?
proliferative phase right after menstruation
What happens to the uterine lining if fertilization does not take place after ovulation? what phase is this?
does not take place, the uterine lining continues to grow for another 14 days (the secretory phase)
Where are testes suspended in? purpose?
Testes are suspended in the scrotum, which keeps them cooler than the body core
Pathway of sperm?
- -Mature sperm flow from the seminiferous tubules into the epididymis, a coiled storage tubule-attached to the surface of each testis
- -Rhythmic muscular contractions of the epididymis move sperm into the vas deferens, which leads into the urethra
Where are sperm produced? how long does this take?
Sperm are produced in seminiferous tubules – the entire process, from spermatogonium to sperm, takes 9 to 10 weeks
How much sperm is produced a day?
around 130 million
What are sertoli cells? hormones involved?
surround developing spermatocytes in the seminiferous tubules – they supply nutrients and seal spermatocytes off from the body’s blood supply
stimulated by FSH
What are leydig cells? hormones involved?
located in the tissue surrounding the developing spermatocytes produce male sex hormones (androgens), particularly testosterone
stimulated by LH
What does seminal vesicles secrete?
thick seminal fluid containing prostaglandins into the vasa deferentia
Location and function of prostate gland?
surroundstheregion where the vasa deferentia join the urethra, adds an alkaline secretion that raises semen pH and activates motility of the sperm
What does the bulbourethral glands secrete? function?
secretes a clear, mucus-rich fluid into the urethra which lubricates the tip of the penis and neutralizes the acidity of residual urine in the urethra
What percentage of sperm is in semen?
less than 5%
When can a human egg be fertilized?
only while it is in the third of the oviduct nearest the ovary
Advantage of more than one sperm trying to fertilize egg?
Although only one sperm fertilizes the egg, the combined release of acrosomal enzymes from many sperm greatly increases the chance of penetrating the zona pellucida
When does the embryo implant in the uterus?
around 7 days after ovulation
What hormones are involved in implantation? function?
During and after implantation, cells associated with the embryo secrete human chorionic gonadotropin (hCG), which keeps the corpus luteum from breaking down
What takes over the secretion of progesterone around 10 weeks after implantation? what happens to the corpus luteum?
placenta, the hCG levels drop and corpus luteum regresses but continues to secrete the hormone relaxin
What is the function of relaxin?
inhibits contraction of the uterus until the time of birth
What is infertility defined as?
inability of the female to get pregnant after 12 months of frequent, contraceptivefree intercourse
What are some causes of male infertility?
low sperm concentration or motility, erectile dysfunction or duct blockage, or health and lifestyle issues
What are some causes of female infertility?
inflammation of the Fallopian tubes, hormone deficiencies, or various environmental factors – athletes may experience athletic menstrual cycle irregularities
What are the 3 techniques for contraception?
- Preventing fertilization
- Preventing ovulation
- Interfering with implantation if fertilization does occur
What is the rhythm method?
avoiding intercourse during the time of the month when the egg can be fertilized
What can latex condoms prevent?
disease transmission
What is a diaphragm?
used with spermicidal jelly blocks the cervix in females
What are surgical preventions to fertilization?
vasectomy and tubal ligation
What are the 2 types of oral contraceptives?
combination of estrogen and progestin, or progestin alone
How does the the pill work?
inhibiting secretion of FSH and LH by the pituitary – without these hormones, ovulation does not occur
Side effects for women who smoke and take the pill?
increased risk of heart attacks and strokes
When does the morning-after pill work?
72 hours after intercourse
What does Mifepristone (RU-486) do?
blocks progesterone receptors in the uterine lining – this initiates a menstrual period, removing any embryo that may have implanted
What timeframe is Mifepristone (RU-486) approved for in the US?
up to 49 days post-conception, only available by prescription
