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71 terms

Chapter 48: Animal Reproduction

Freeman, 4th Ed.
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How are the different ways that animal reproductive systems are highly variable?
1. many animals can switch between asexual and sexual reproduction
2. when sexual reproduction occurs, fertilization may be external or internal
3. egg development may take place inside or outside the mother's body
What is asexual reproduction?
occurs without fusion of gametes; based on mitosis; offspring are genetically identical to their parent
What is sexual reproduction?
occurs as a result of gamete fusion; based on meiosis; offspring genetically different from each other and parents
How does asexual reproduction occur?
1. Budding
2. Fission
3. Parthenogenesis
What is budding?
offspring begins to form within or on a parent; process completed when offspring breaks free and begins to grow on its own; offspring = mini parent (example: Hydra)
What is fission?
individual splits into two descendants (example: tubellerin flat worm, soft coral)
What is parthenogenesis?
female offspring develop from unfertilized eggs (offspring are genetically equal to the mother); only girls can do this!
What is the result of parthenogenesis?
all individuals in population are females
In Daphnia, what signals the switch from asexual to sexual reproduction?
environmental cues: water quality, food concentration, day length (crowded water, low food, and short days signal sexual reproduction)
What is gametogenesis?
mitotic cell divisions, meiotic cell divisions, and developmental events that result in the production of male and female gametes
In the vast majority of animals, gametogenesis occurs in the ________.
sex organs, or gonads
_______ are male sex organs, and _________ are female sex organs.
testes; ovaries
Describe the process of spermatogonia forming sperm in males.
1. spermatogonia (2n) divide by mitosis to produce primary spermatocytes (2n)
2. primary spermatocytes undergo meiosis I and produce two secondary spermatocytes (n)
3. secondary spermatocytes (n) undergo meiosis II to form four spermatids (n)
4. each spermatid (n) matures into a sperm (n)
Describe the process of oogonia forming an egg in females.
1. oogonia (2n) divide by mitosis to form primary oocytes (2n)
2. primary oocytes (2n) undergo meiosis to form four haploid products
3. only one of haploid products, known as ovum (n) matures into egg (n)
4. other cells do not mature into eggs; they form polar bodies (n)
When does the primary oocyte complete meiosis I?
during the menstrual cycle
When does the secondary oocyte complete meisis II?
only once fertilization has started to occur
What is the polar body?
just DNA with cytoplasm/cell membrane
What is the purpose of non-symmetric cell division in the formation of eggs?
this allows for an extremely large egg (with all cytoplasm, organelles, etc.) to develop but only half the DNA
Why doesn't the egg complete all rounds of meiosis before fertilization?
egg gets far enough in process to complete the division in case there is fertilization, but not too far so as to waste resources
What is a simultaneous hermaphrodite?
each individual has both functional testes and ovaries; two individuals required for mating; each fertilizes the other (earthworms, snails)
What is a sequential hermaphrodite?
either female or male first, then the other; switch is triggered by environmental cues (some invertebrates, some fishes)
What are the two types of sequential hermaphrodites?
1. protogynous (female first)
2. protandrous (male first)
What are characteristics of external fertilization?
most in aquatic environments; tend to produce huge numbers of gametes; gamete release must be coordinated and may involve pheremones; gametogenesis occurs in response to environmental cues such as lengthening days and warmer water temperatures (which indicate a favorable season for breeding)
What is copulation?
males deposit sperm directly into female reproductive tract
What is a spermatophore?
sperm packet placed into female's reproductive tract by male or female
What is second-male advantage?
experimentally, whichever male was last to copulate fathered an average of 85% of offspring; type of sperm competition
What is cryptic female choice?
females choose which male is the last to copulate; females physically eject sperm from undesirable males (absence of male awareness)
What is the baculum?
penis bone, physical support bone in many mammals (which sperm competition comes increase in testes and penile size)
What does oviparous mean?
egg laid outside mother's body and embryo develops in external environment
What dies viviparous mean?
egg remains within mother's body; development takes place there (Embryo receives nutrition direction from mother)
What does ovoviparous mean?
offspring develop inside mother's body but nourished by nutrient-rich yolk stored in egg
In humans, the male reproductive system consists of:
1. scrotum (sac that holds the testes)
2. penis (organ of copulation prior to internal fertilization)
What are the three basic functional components of the male reproductive system?
1. spermatogenesis and sperm storage
2. production of additional fluids
3. transport and delivery
Sperm are produced in the _____ and stored in the ____.
testes; epididymis
What is semen?
combination of sperm and accessory fluids
What does the vas deferens do?
transport sperm from epididymis to duct in prostate gland
What tube does semen get ejaculated from?
urethra
What is a flaw in the design of the male reproductive system?
urinary bladder sits on top of the prostate gland (prostate continues to grow as males age, puts pressure on the bladder and urethra)
How is the orgasm an example of positive feedback in males?
urethra fills with semen; activate pressure receptor neurons; contraction of cavernosus muscle; pressurize contents of urethra which leads back to activate pressure receptor neurons (ultimately leads to explosive release)
How long does it take to make sperm in humans?
70-80 days (but production is continuous at about 200,000,000 per day
Sperm maturation is faulty above _____ degrees.
95 degrees F
What does the cremaster muscle do?
raises/lowers testes to regulate temperature
What do the seminal vesicles carry?
1. fructose (source of chemical energy for sperm movement)
2. prostaglandins (stimulate smooth-muscle contractions in uterus)
What does the prostate gland carry?
1. antibiotic compound (prevent urinary tract infections in males(?))
2. citric acid (nutrient used by sperm)
What does the bulbourethral gland carry?
1. alkaline mucus (lubricates tip of penis; neutralizes acids in urethra)
How does external anatomy affect sperm competition?
variation in the size and shape of male genitalia (external reproductive organs) may have a strong impact on male reproductive success
The most important part of female reproductive system is the _______, organ in which egg cells (ova) are produced.
ovary
The external anatomy of the female reproductive system consists of:
1. labia minora and labia majora
2. clitoris
3. vagina
What are the labia minora / labia majora?
folds of skin that cover urethral and vaginal openings
What is the clitoris?
sensitive organ that develops from same embryonic cells that give rise to male penis
What is the vagina?
chamber where semen is deposited during sexual intercourse and through which a baby is delivered during childbirth (birth canal)
The first 14 days of the ovarian cycle is called:
the follicular phase
The second 14 days of the ovarian cycle is called:
the luteal phase
If the female doesn't get pregnant, the follicle degenerates into:
the corpus luteum
Human females are born with about __________ diploid oogonia, all that will ever be made by mitosis.
400,000 (made before birth, during embryogenesis)
About how many oocytes will develop in a female?
puberty to menopause is about 30 years (12 oocytes per year), means about 400 oocytes that will develop
What are the two functions of the female reproductive system?
1. production and transport of eggs
2. development of offspring
What happens during ovulation?
an egg is expelled from ovary and enters oviduct, where fertilization may take place (fertilized eggs that transported to uterus)
How long after ejaculation can sperm become motile?
1-10 hours (sperm can survive 1-2 days in female genital tract)
The trip down the oviduct takes about _________ whether egg fertilized or not.
one week (due to cilia beating)
An ovulated oocyte only survives for ____.
24 hours (so many oocytes in transit are duds)
Describe the cervical secretion before and after ovulation.
during ovulation, cervical secretions become runny and more conducive to sperm swimming through; after ovulation secretions are thick and pasty to block sperm (with successful implantation, secretions are so thick as to completely block off uterus)
The main male sex hormone is ______ and the main female sex hormone is ______.
testosterone; estradiol
Where is testosterone synthesized?
in specialized cells inside the testes
Where are estradiol and other estrogens produced?
in the ovaries by cells that surround the developing egg, which form a structure called a follicle
How do hormones control puberty in mammals?
1. gonadotropin-releasing hormone (GnRH) is released from the hypothalamus
2. triggers release of luteinizing hormone (LH) and follicle-stimulating hormone (FSH) from pituitary gland
3. LH and FSH then trigger increases in testosterone and estradiol
Which animals menstruate?
humans and other great apes
Female animals that do not menstruate have an ____________.
estrous cycle
What happens during the follicular phase of menstruation?
follicle matures and ovulation occurs
What happens during the luteal phase of menstruation?
corpus luteum forms from ruptured follicle and subsequently degenerates
During what part of the menstrual cycle are the levels of LH/FSH highest?
during ovulation