Chapter 15 Animal Reproduction Flashcards
Distinguish between asexual and sexual reproduction.
Sexual reproduction is the formation of offspring by
the fusion of haploid gametes to form a diploid zygote.
Asexual reproduction is the formation of individuals
whose genes come from a single parent.
List and describe four mechanisms of asexual reproduction.
- Fission
• Parent separates into two or more approximately equal-sized individuals (e.g., some species of Cnidarians, Platyhelminthes, Annelids) - Budding
• New individuals form in or on the parent, and a miniature version of the parent eventually breaks free to live on its own (e.g., Hydra). - Fragmentation and regeneration
• Body breaks into several pieces and pieces regenerate lost parts(e.g., sea stars, sponges). - Parthenogenesis
• Female offspring develop from unfertilized eggs.
(e.g., Rotifers, some crustaceans, some bees, wasps, and ants, several genera of fish, amphibians, and lizards)
Describe the circumstances under which asexual reproduction would be advantageous.
When a lot of offspring needs to be produced at one time, when it is hard to find a mate, when there isnt a lot of energy
Describe two hypotheses for the advantages of sexual reproduction.
- –Produces diverse offspring - may enhance the reproductive success of parents when environmental factors, such as pathogens, change rapidly.
- –Shuffling of genes during sexual reproduction may allow populations to rid themselves of harmful genes more readily.
Explain how hermaphroditism may be advantageous in sessile or burrowing animals.
Sexual reproduction presents a problem for sessile or burrowing animals or parasites.
• Difficult to encounter a member of the opposite sex.
• An evolutionary solution = hermaphroditism
• One individual functions as both a male and a female.
• Some hermaphrodites can self-fertilize, but most mate with another member of the same species.
• Each individual receives and donates sperm, resulting in twice as many offspring as would be produced if only one set of eggs were fertilized.
Briefly describe an example of an animal life cycle that alternates between asexual and sexual reproduction.
Daphnia (water fleas) reproduce by parthenogenesis under favorable conditions and switch to sexual reproduction during times of environmental stress.
Describe spermatogenesis and oogenesis.
Spermatogenesis:
Diploid spermatogoniumdivides via mitosisto generate primary spermatocytes.
• Each primary spermatocyte divides via meiosis to give rise to four spermatids.
• Each spermatid matures into a sperm.
Oogenesis: • Diploid oogoniumdivides by mitosis to generate a primary oocyte. • Primary oocyte undergoes meiosis. • Uneven cytokinesis. • Only one of the 4 haploid cells survives to mature into an egg= ovum.
Describe three major differences between oogenesis and spermatogenesis.
- Spermatogenesis: all four products of meiosis develop into mature gametes.
Oogenesis: unequal cytokinesis during meiosis results in the formation of a single large secondary oocyte (becomes egg) and smaller polar bodies that degenerate. - Spermatogenesis: occurs throughout adolescence and adulthood. Ooogenesis: at birth, an ovary contains all the primary oocytes it will ever have, and the production of mature gametes ceases at about age 50.
- Spermatogenesis: produces mature sperm from precursor cells in a continuous sequence.
Oogenesis: has long “resting” periods.
Describe mechanisms that increase the probability that mature sperm will encounter fertile eggs of the same species in organisms that use external fertilization.
- Most animals that rely on external fertilization live in aquatic environments – why?
- A moist habitat is required to 1) prevent gametes from drying out and 2) allow the sperm to swim to the eggs.
- Species that use external fertilization also tend to produce large numbers of gametes – why?
- To increase the probability that sperm and egg will actually meet.
- External fertilization also requires careful timing – why?
- Crucial to ensure that mature sperm and eggs encounter one another.
- Methods:
- Spawning
- Courtship
- Pheromones
Define and explain the function of pheromones.
A pheromone is a chemical an animal produces which changes the behavior of another animal of the same species (animals include insects). Some describe pheromones as behavior-altering agents. Many people do not know that pheromones trigger other behaviors in the animal of the same species, apart from sexual behavior.
Pheromones, unlike most other hormones are ectohormones - they act outside the body of the individual that is secreting them - they impact a behavior on another individual. Hormones usually only affect the individual that is secreting them.
Differentiate between internal and external fertilization on the basis of the relative number of zygotes and protection of the eggs + embryos.
Internal Fertilization: Fewer gametes, but higher survival of zygotes
External fertilization: more gametes but less survival rate
Describe sperm-competition and the second-male advantage.
Sperm competition: competition between sperm from
different males to fertilize the eggs of the same female.
Proportion of offspring fertilized by two males that mated with a single female was not 50:50, but rather the male that was last to copulate fathered on average 85% of the offspring produced.
• This is referred to as the second-male advantage.
• Sperm from the second male may actually dislodge or poison the first male’s sperm from the female’s sperm storage area.
Define “female cryptic choice”.
Females in some species do play a role in sperm selection, in a process called female cryptic choice.
• Female actively chooses which male performs the last copulation before fertilization takes place.
List and describe several fascinating behaviors or structures related to sexual reproduction (e.g., femmes fatales, love darts…etc
infidelity, cross dressers, love darts and femmesfatalas
Describe and give the function of each component of the reproductive system of the human female.
Gonads = ovaries.
• Each ovary contains many follicles.
• Consist of an oocyte surrounded by support cells.
• Nourish and protect the oocyte during oogenesis.
• Only about 500 fully mature between puberty and menopause, releasing a secondary oocyte during ovulation near opening of oviduct.
Corpus luteum develops from follicular tissue after ovulation.
• Secretes hormones to help maintain the uterine lining during pregnancy.
Endometrium: highly vascularized inner lining of the uterus.
Describe and give the function of each component of the reproductive system of the human male.
Gonads = testes.
• Seminiferous tubules = highly coiled tubes where sperm are produced.
Leydig cells = cells scattered in the connective tissue between the seminiferous tubules that produce testosterone and other androgens (steroid hormones).
Scrotum = fold in the body wall, holds the testes outside the body cavity at a temperature appropriate for spermatogenesis.
Epididymis = coiled tubules in which sperm are stored and mature.
Vas deferens = muscular duct through which sperm are propelled during ejaculation.
Describe the function of fluid secreted by each of the 3 accessory glands that add to semen.
- Seminal vesicles - contribute about 60% of total semen volume.
• Contains mucus, fructose (an energy source for sperm), a coagulating enzyme, ascorbic acid, and prostaglandins (hormone-like substance). - Prostate gland – secretes fluid directly into the urethra.
• Contains anticoagulant enzymes and citrate, a sperm nutrient.
• Prostate cancer is one of the most common cancers in men. - Bulbourethral glands - small glands along the urethra below the prostate.
• Prior to ejaculation, the bulbourethral glands secrete clear mucus that neutralizes any acidic urine remaining in the urethra.
Describe the influence of androgens on primary and secondary sex characteristics and
behavior
During embryogenesis, androgens direct
the development of primary sex characteristics of males.
• = structures directly involved in reproduction
At puberty, sex hormones in both males and females induce formation of secondary sex characteristics.
• = physical and behavioral features not directly related to reproductive system.
Explain and diagram the functions of GnRH, LH, FSH, inhibin, and testosterone in male gametogenesis (including negative feedback ).
• Hypothalamus
Secretes: gonadotropin-releasing hormone (GnRH)
Stimulates production of FSH and LH.
• Anterior pituitary
Secretes: follicle-stimulating hormone (FSH), luteinizing hormone (LH).
Stimulates production of sex hormones in gonads.
• Testes
Secrete androgens (e.g., testosterone)
• Ovaries
Secrete estrogens (estradiol and progesterone)
Explain how the uterine cycle and ovarian cycle are synchronized in female mammals.
Hormone activity links the two cycles, resulting in the
synchronization of ovarian follicle growth and ovulation with the establishment of a uterine lining that can support
embryonic development.
Compare and contrast menstrual cycles and estrous cycles.
Estrous cycles
• All female mammals undergo a thickening of the endometrium prior to ovulation, but only humans and certain other primates have menstrual cycles.
• Other mammals have estrous cycles.
• If pregnancy does not occur, the uterus reabsorbs the endometrium with little fluid flow.
• Period of sexual activity (“estrus”) is the only time the female is receptive to mating.
• The length and frequency of reproductive cycles vary widely among mammals.
• Bears and wolves: one estrous cycle per year.
• Elephants: several per year.
• Rats: throughout the year, each lasting only five days.
Describe human menopause. Describe a possible evolutionary explanation for human menopause.
• Menopause
• After about 500 cycles cessation of ovulation and
menstruation.
• Ovaries lose their responsiveness to FSH and LH decline in estradiol production by the ovary menopause.
• In most other species, females and males retain their
reproductive capacity throughout life.
• One evolutionary hypothesis: cessation of reproduction allowed a woman to provide better care for her children and grandchildren –> increased survival of individuals bearing her genes and thus her fitness.
Compare/contrast the patterns of hormone secretion and reproductive events in male and female mammals.
• In contrast to males, which carry out gametogenesis
continuously in adolescence and adulthood, females produce gametes in cycles.
• Two closely linked cycles characterize reproduction in human females.
• Cyclic events that occur in the ovaries define the ovarian cycle.
• Cyclic changes that occur in the uterus define the uterine cycle (or menstrual cycle).
Describe the events that occur between fertilization and implantation in human females.
• Once the oocyte and sperm membranes fuse, the oocyte nucleus completes meiosis II.
• Nucleus of the sperm and egg unite, forming the diploid zygote.
• 24r hours after fertilization: zygote begins dividing = cleavage.
• 3-4 days after fertilization: embryo reaches the uterus as a ball of 16 cells.
• ~ 5 days after fertilization: a sphere of cells surrounding a central cavity forms = blastocyst.
• After a few more days, the blastocyst implants in the
endometrium.
