Ch 46 Animal Reproduction Flashcards
Sexual reproduction
The creation of an offspring by fusion of a male gamete (sperm) and female gamete (egg) to form a zygote
Asexual reproduction
The creation of offspring without the fusion of egg and sperm
How do many invertebrates reproduce asexually?
Fission
Fission
Separation of a parent into two or more individuals of about the same size
Form of asexual reproduction
Budding
New individuals arise from outgrowths of existing ones
Form of asexual reproduction
Fragmentation
Breaking of the body into pieces, some or all of which develop into adults
Form of asexual reproduction
Parthenogenesis
The development of a new individual from an unfertilized egg
In what organisms does parthenogenesis occur?
1) In many plants
2) Some invertebrates
3) Some vertebrates (amphibians and reptiles)
What is one example of parthenogenesis occurring in vertebrate?
Aspidoscelis (whiptail lizards)
In how many species of Aspidoscelis does parthenogenesis occur?
15
How did the species of Aspidoscelis that reproduce by parthenogenesis arise?
From hybridization among sexual species
What is the “twofold cost” of sexual reproduction?
Sexual females have half as many daughters as asexual females
Do most eukaryotic species reproduce sexually or asexually?
Sexually
Why does sexual reproduction provide potential advantages over asexual reproduction?
It results in genetic recombination
Potential advantages of sexual reproduction
1) Increases the variation in offspring, providing an increase in the reproductive success in changing environments
2) Increases the rate of adaptation
3) Shuffles the genes and eliminates harmful genes from a population
Most animals exhibit reproductive cycles related to what?
Changing seasons
Most animals exhibit reproductive cycles controlled by what two things?
1) Hormones
2) Environmental cues
Ovulation
The release of mature eggs at the midpoint of a female cycle
Are reproductive cycles and mating behaviors retained in asexual whiptail lizards (Aspidoscelis)?
Yes
Gonads
The organs that produce gametes
In addition to gonads, many animals possess what?
Accessory organs
Involved in the transfer and reception of sperm
Spermatheca
Organ in many female insects where sperm is stored during copulation
Cloaca
A common opening for digestive, excretory, and reproductive systems
Typically found in nonmammalian vertebrates
Female external reproductive structures of humans
1) Sensory clitoris
2) Two sets of labia
Female internal reproductive structures of humans
1) Pair of gonads
2) System of ducts and chambers that carry gametes and house the embryo and fetus
Male external reproductive structures of humans
1) Penis
2) Scrotum
Male internal reproductive structures of humans
1) Gonads
2) Accessory glands
Vagina
Thin-walled chamber that is the repository for sperm during copulation
Serves as birth canal
Each ovary contains many what?
Follicles
Follicle
Contains an oocyte
Oocyte
A partially developed egg
Ovum
A fully developed egg
Oogenesis
Process where an oocyte develops into an ovum
Oviduct (fallopian tube)
Tube through which the ovum cell travels from the ovary to the uterus
Endometrium
Uterus lining
How does the endometrium support egg development?
It has many blood vessels
Seminiferous tubules
Site of sperm formation
Found in the testes
Leydig cells
Produce hormones
Scattered between the tubules
Sperm passes from the testes to what?
The epididymis
During ejaculation, sperm is propelled through what two structures?
1) Vas deferens
2) Ejaculatory duct
Urthera
Structure through which sperm exits the penis
The human penis is composed of what?
Three cylinders of spongy erectile tissue
What causes an erection?
During arousal, the erectile tissue fills with blood from the arteries
Semen
Composed of sperm and secretions from three sets of accessory glands
Three accessory glands that help form semen
1) Two seminal vesicles
2) Prostate gland
3) Bulbourethral glands
Seminal vesicles
Contribute ~60% of the total volume of semen
Prostate gland
Secrets its products directly into the urethra through several small ducts
Bulbourethral glands
Secrete a clear mucus before ejaculation that neutralizes acidic urine remaining in the urethra
Spermatogenesis
The development of sperm
How many sperm are produced each day?
Millions
How long does it take each sperm to develop?
7 weeks
Oogenesis
The development of an egg
Ovulation
The monthly release of a mature egg
How many of the products of meiosis develop into sperm?
All four
How many of the products of meiosis develop into an egg?
One of the four
What are the two main male reproductive hormones?
1) Follicle stimulating hormone (FSH)
2) Leutenizing hormone (LH)
Follicle stimulating hormone (FSH)
Promotes the activity of Sertoli cells
Sertoli cells
Nourish developing sperm
Leutenizing hormone (LH)
Regulates Leydig cells
Leydig cells
Secrete tetosterone and other androgens
Testosterone and other androgens promote what?
Spermatogenesis
What closely links the two cycles of female reproduction?
Hormones
Ovarian cycle
Female reproductive cycle defined by changes in the ovaries
Menstrual cycle (uterine cycle)
Female reproductive cycle defined by changes in the uterus
What happens to the endometrium before ovulation?
It thickens in preparation for embryo implantation
Menstruation
Shedding of the endometrium
Occurs if an embryo does not implant into the endometrium
What three hormones stimulate follicle growth?
1) Follicle stimulating hormone (LSH)
2) Leutenizing hormone (LH)
3) Gonadotropin releasing hormone (GnRH)
Follicle growth and an increase in the hormone estradiol leads to what?
Ovulation and the release of a secondary oocyte (mature egg)
Where do immature eggs form?
The female embryo
When do eggs complete their development?
Many years after birth
What does the follicle become after releasing an egg?
The corpus luteum
The corpus luteum secretes what two hormones to maintain pregnancy?
1) Estradiol
2) Progesterone
Human chorionic gonadotropin (hCG)
Hormone released by the embryo to prevent menstruation
How does the embryo obtain nutrients for the first 2 to 4 weeks?
Directly from the endometrium
What forms the placenta?
Mingling between the trophoblast and endometrium
What is one of the few examples of positive feedback loops in humans?
Hormonal controls in birth
What replaces the menstrual cycle in most animals?
Estrous cycle
Estrous cycle characteristics
1) Endometrium is reabsorbed by the uterus
2) Sexual receptivity is limited to a “heat” period
3) Length and frequency of the estrous cycles vary from species to species
