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Both Asexual and sexual reproduction occur in the animal kingdom
: the fusion of haploid gametes forms a diploid cell,
Animals that develop from zygotes can in turn give rise to gametes by meiosis.
Female gamete is called the
It is large and does not move
Male gamete is called the
. It is smaller than the egg and it can move
: is the making a new individuals without the fusion of egg and sperm.
Most asexual animals rely on mitotic cell division
Mechanisms of Asexual Reproduction
Many invertebrates can reproduce asexually by fission.
: the separation of a parent organism into two individuals of approximately equal size
individuals arise from outgrowths of existing ones
2 Step Process fragmentation and regeneration
Fragmentation: breaking the body in several pieces
Regeneration: regrowth of lost body parts
: form of asexual reproduction in which an egg develops without being fertilized
Reproduction by parthenogenesis happens in certain species of bees, wasps, and ants.
progeny can be either haploid or diploid
If it is a haploid, the offspring develop into adults that produce eggs or sperm without meiosis.
Sexual Reproduction: An Evolutionary Enigma
Sex creates diverse combinations of parental genes made during meiotic recombination and fertilization.
Sexual reproduction may enhance the reproductive success of parents when environmental factors change rapidly.
Asexual reproduction is most advantageous in favorable environments because it copies the genotypes precisely from one generation to the next.
Sexual reproduction can be advantageous because beneficial gene combinations arising through recombination might speed up adaptation.
Significant when the rate of beneficial mutations is high and population size is small
Reproductive Cycles and Patterns
Animals exhibit cycles in reproduction to conserve resources such as reproducing only when sufficient energy sources or stores are available and when environmental conditions favor the survival of offspring.
: the release of mature eggs, which occurs during the midpoint of each cycle
Reproductive cycles are controlled by hormones, which are regulated by environmental cues.
Common environmental cues are changes in day length, seasonal temperature, rainfall, and lunar cycles
Animals generally reproduce only at certain times of a year.
Animals may alternate between asexual and sexual reproduction cycles.
In Aphids, rotifers, and water fleas, the females demonstrate both types.
Water Flea Daphnia
Several genera of fishes, amphibians, and reptiles reproduce exclusively by a complex form of parthenogenesis that involves the doubling of chromosomes after meiosis, producing diploid offspring.
Ovulation is more likely to occur if the individual is mounted during the critical time of the hormone cycle
became the evolutionary solution to sessile animals who are not able to encounter the opposite sex.
: each individual has both male and female reproductive systems.
Any two individuals can mate
Some hermaphrodites are capable of self-fertilization
Example - earthworms
Another reproductive pattern involves sex reversal, in which an individual changes its sex during its lifetime.
Examples - bluehead wrasse and oyster species
SECTION 2: Fertilization depends on mechanisms that bring together sperm and eggs of the same species
What is Fertilization?
is the union of a sperm and egg.
In external fertilization, the female releases eggs into the environment, where the male fertilizes them.
External fertilization requires a moist environment to prevent gametes from drying out and for the sperm to be able to swim to the eggs
In external fertilization, physical contact not necessary; however timing in crucial to ensure that the gametes from the parents meet
Synchronized Release of Gametes
Individuals of a certain species release their gametes into the water at the same time
Sometimes, chemical signals trigger certain individuals to release their gametes
Changes in day length triggers some animals to release their gametes
Unsynchronized Release of Gametes
Advantages of unsynchronized release of gametes include: mate selection and release of eggs and sperm at the same time, which result in better survival rates for the offspring
In internal fertilization, sperm from the male is deposited in or near the female reproductive tract.
In internal fertilization, fertilization occurs within the tract
Internal fertilization requires compatible reproductive systems and structures
Copulation usually occurs along with internal fertilization
Male copulatory systems deliver sperm
Female reproductive tracts have receptacles to store sperm
The female reproductive tracts also deliver sperm to mature eggs
Pheromones, like hormones, are signaling molecules that are released into the environment to attract potential mates
Ensuring the Survival of Offspring
All species tend to produce more offspring than can survive
External Fertilization tends to produce more gametes, but only a few zygotes develop
Internal Fertilization tends to produce less gametes, and there is greater protection for the embryo such as parental care
Animals have special adaptations to protect them when they are in developmental and embryonic stages
Some animals remain only in the uterus for a while (For example, some marsupials leave the uterus after a while and attach themselves to a mammary gland and continue fetal development)
Placental animals remain in the uterus throughout fetal development; the mother’s blood supply’s the embryo through a specialized organ—the placenta.
Parental care (Many mammals, including humans, provide parental care. Birds and some reptiles and amphibians also ensure parental care)
Gamete Production and Delivery
During embryogenesis, precursor cells are created that remain inactive throughout development. Sexual reproduction relies on these precursor cells for the production of ova and sperm
Later, these precursor cells are amplified in number
are the organs that produce gametes
In some animals, gametes are derived from undifferentiated cells of the body cavity (coelom)
Most insects have separate sexes and complex reproductive systems
Sperm are stored in seminal vesicles and deposited in female reproductive tracts
Eggs are produced in the ovaries and fertilized in the vagina
are sperm storing sac carried in females
Parasitic worms are hermaphroditic, which means they have both female and male reproductive structures
Many vertebrates, with the exception of mammals, have a common opening (cloaca) for excretory waste and reproductive systems.
Mammals have separate openings for the excretory and reproductive systems
Mechanisms influence the success of fertilization
SECTION 3: Reproductive organs produce and transport gametes
Female Reproductive Anatomy
Ovaries are female gonads that held by ligaments in the abdominal cavity
, which are filled with
which are partially developed eggs, surrounded by support cells
the support cells nourish and protect the cells during oogenesis, the formation and development of an ovum
Menstruation/ Ovulation is when 1 follicle is released and expels an egg
A primary female sex hormone is Estradiol
After ovulation, a tissue called the corpus luteum secretes estradiol with progesterone which helps form the uterine lining during pregnancy
Oviducts and Uterus
Oviducts (or fallopian tube) connect the ovaries to the uterus and the vagina
Cilia on the epithelial lining help when an egg is traveling down the oviduct.
The Uterus is the womb!
The richly supplied lining full of blood vessels is the endometrium
The Cervix is the opening to the vagina
Vagina and Vulva
is the muscular yet elastic chamber used for the insertion of the penis!
is just a collective term for the external female genitals
protects & encloses the vulva
is a cavity surrounded by slender skin folds
A thin piece of tissue called the
covers the vaginal opening until it is ruptured by physical activity or sex
AKA POPPING THEM CHERRIES
The Clitoris is a short shaft of with a rounded
(or head) that is covered by a small hood of skin called the prepuce
During sexual arousal, the clitoris, vagina, and labia minora all engorge with blood and secrete lubricating mucus, facilitating sex.
s are present in both sexes but produce milk in females.
Within the glands, small sacs of epithelial tissue secrete milk, which drain into a series of ducts at the nipple
Because of the low level of estradiol in males, male breasts remain small.
Male Reproductive Anatomy
Testes are male gonads which are coiled tubes surrounded by connective tissue
The tubes are
where sperm is formed
, located in seminiferous tubules, produce testosterone and androgens
Sperm is only produced when the testes are cooler than body temperature
achieves this by maintaining testis temperature about 2˚C below the abdominal cavity
Testis within a scrotum = testicle
In the seminiferous tubules, sperm passes into coiled tubes of the
During the passage, the sperm completes their maturation and become motile, but only fertilize when in the female reproductive system
sperm is propelled through a muscular duct called the vas deferens
extends around the urinary bladder, where it joins the seminal vesicle called the
The Urethra is the outlet tube for excretory and the reproductive system
There are 2 of them
contribute to 60% of semen
Semen: Thick, yellowish, and full of alkaline
contains mucus, fructose, enzyme, ascorbic acid, and prostaglandins
contains thin fluid made of anticoagulant enzymes and citrate
Cause of some of the most common medical problems in men aged 40+
Benign cancer occurs in half of the men and enlargement occurs in almost all men over 70+
secrete clear mucus that neutralizes acidic urine remaining in urethra before ejaculation
Contains the urethra & 3 cylinders of spongy erectile tissue
Erections= gorge of blood and sealing of pressure
alcohol, drugs, emotional issues, and aging can cause erectile disfunction
main shaft of the penis is thick skin
glans are mich thinner and sensitive to simulation
Human Sexual Response
Sexual response in Males and Females
: filling of tissue with blood
: increased muscle tension
Step One: Excitement
Vasocongestion is evident in breasts, penis, labia and mytonia may occur in arms and legs
Step Two: Plateau
Breathing and heart rate increases, and depression for receiving sperm occurs in the back of the vagina
Emission~ glands and duct contract
Ejaculation~ urethra contracts and semen is expelled
Orgasms only last 0.8 seconds
Step Four: Resolution
Vasocongested organs relax
SECTION 4: The timing and pattern of meiosis in mammals differ for males and females
is the production of gametes
Gametogenesis differs in males and females
occurs continuously in the testes (within the seminiferous tubules)
Spermatogonia are the stem cells that give rise to sperm
Sperm are small and motile
Spermatogonia produce spermatocytes that undergo meiosis to produce spermatids (There are four spermatids at the end of meiosis)
The head of the sperm consists of a haploid nucleus and acrosome, which contains enzymes that help the sperm penetrate the egg
The energy required for the movement of the flagellum, or tail, comes from the ATP provided by the mitochondria
occurs in the female embryo.
Oogonia are produced from the primordial germ cells
Eggs, however, are large and not motile
Eggs hold the initial food stores for the embryo
These germ cells divide into primary oocytes, which are arrested in prophase I before birth
During puberty, FSH stimulates the oocytes to undergo meiosis, and the oocystes are allowed to complete meiosis I. These oocytes are known as secondary oocytes and are arrested in metaphase II
In humans, meiosis II is completed only when a sperm penertrates the oocyte
Meiotic cytokinesis is unequal, which produced one large ovum and three smaller haploid polar bodies that disintegrate
SECTION 5: The interplay of tropic and sex hormones regulates mammalian reproduction
LH and FSH regulate gametogenesis directly through target tissues in the gonads and indirectly by regulating sex hormones production
principal sex hormones are steroid hormones
In males, androgens such as testosterone
In females, estrogen such as estradiol and progesterone
Androgens promote the development of the primary sex male characteristics, such as structures involved in reproduction.
causes the voice to deepen, facial and pubic hair to develop, and muscles to grow
increases general aggressiveness
At puberty estradiol stimulates breast and pubic hair
induces fat deposition in the breasts and hips, increases water retention, and changes calcium metabolism
Hormonal Control of the Male Reproductive System
FSH and LH are both required for normal spermatogenesis.
FSH promotes the activity of Sertoli cells, which nourish developing sperm
LH promotes Leydig cells secrete testosterone in the tubules.
Two negative-feedback mechanisms control sex hormone production in males.
GnRH, FSH, LH effects on the hypothalamus and pituitary.
Inhibin, hormone that is produced by Sertoli cells, acts on the anterior pituitary gland to reduce FSH secretion.
The Reproductive Cycles of Females
The cyclic shedding of the endometrium from the uterus is called
Cyclic events that take place in the ovaries is called the
Growing of the follicle
Maturing of the follicle
FSH and LH increases until ovulation begins to happen
Estradiol is secreted by growing follicle in increasing amounts.
Development of the corpus luteum
Degeneration of the corpus luteum.
Progesterone and estradiol is secreted by corpus luteum.
Changes that define changes in the uterus is
, also known as
endometrium regenerates and thickens.
endmetrium continues to thicken, becomes vascularized, and develops glands that secrete a fluid rich in glycogen.
Menstrual flow phase:
menstrual bleeding occurs
, a disorder in which some cells of the uterine lining migrate to an abdominal location that is abnormal, or
End to ovulation and menstruation
Usually around the ages of 46 and 54
lose their responsiveness to FSH and LH, resulting in a decline in estradiol production by the ovary.
Menstrual Versus Estrous Cycles
Only humans and certain primates have menstrual cycles
Other mammals have
cycles, in the absense of a pregnancy, the uterus reabsorbs the endometrium and no extensive fluid flow occurs.
Estrus, a period of sexual activity is the only time a female is receptive to mating.
Estrus is also called heat and the female's body temperature increases slightly.
Length and frequency of reproductive cycles vary widely among mammals.
SECTION 6: In placement mammals, an embryo develops fully within the mother's uterus.
Conception, Embryonic Development, and Birth
2-5 mL of semen is transferred with 70-130 million sperm in each milliliter.
When first ejaculated, semen coagulates and helps the sperm reach the cervix
Anticoagulants liquefy the semen and sperm begin swimming though the uterus and oviducts
Fertilization- also called
- occurs when a sperm fuses with an egg in the oviduct
The following then occurs...
is implanted into the endometrium, the embryo secretes a hormone that signal its presence and regulates the mother's reproductive system
A hormone is called
Human Chorionic Gonadtrophin (hCG)
In the absence of hormonal override, the corpus luteum would deteriorate, resulting in menstruation
Levels of hCG in maternal blood is so high, some is excreted into urine, a signal of
Human pregnancy averages 266 days from fertilization/ 40 weeks from start of last menstrual cycle
Pregnancies are terminated though chromosomal or developmental abnormalities
If a fertilized egg is lodged in the oviduct, serious internal bleeding may occur.
Human fertilization is divided into three trimesters of three months each
The embryo's body structures begin to differentiate
during the first 2-4 weeks of development, the embryo obtains nutrients from the endometrium
The outer layer of the blastocyst, the
, grows outward and mingles with the endometrium, forming the placenta
is a disk shaped organ made of blood vessels that provides immune protection, exchanges respiratory gases, and disposes metabolic wastes
splitting embryo during first month can result in identical twins (monozygotic) or fraternal twins (dizygotic)
First Trimester is the main period of
, the development of body organs
most susceptible to damage from radiation or drugs
The fetus grows to be about 5 cm long
High levels of progesterone initiate changes in the reproductive system
Uterus grows enough to be obvious
fetus grows to 30 cm
Corpus luteum deteriorates
placenta takes over the production of progesterone
fetus grows 3-4 kg in weight and 50 cm in length
the mother's organs become compressed and displaced, leading to urination, digestive blockages, and strain in back muscles
Prostagladins and hormones induces and regulates
Uterine contractions bring about birth, or parturition
Stage 1: opening and thinning of cervix
Stage 2: delivery of baby
Stage 3: delivery of placenta
is the postnatal care unique to mammals
Maternal Immune Tolerance of the Embryo and Fetus
Contraception and Abortion
Contraception is the deliberate prevention of pregnancy
Contraception can be achieved through abstinence
temporary abstinence, or the
rhythm method / natural family planning
depends on refraining from intercourse when conception is likely
timing ovulation include factors such as changes in cervical mucus and body temperatures during the menstrual cycle.
a 10-20% of pregnancy is reported for couples using natural family planning
withdrawal of the penis before ejaculation is unreliable and sperm from previous ejaculations may be transferred
is one barrier method that leaves pregnancy rates less than 10%
is a dome shaped rubber cap inserted into the upper portion of the vagina before intercourse
Hormonal contraceptives in the form birth control pills have pregnancy rates of 1% or less
the most common
birth control pills
have a combination of synthetic estrogen and progestin
Another hormone based contraceptive contains only progestin which blocks a woman's cervical mucus preventing sperm from reaching the uterus
Progestin is administered several ways: time-release, capsules, injections, and tablets
Cardiovascular problems, abnormal blood clotting, high blood pressure, stroke, heart attack are all risks
however, women on birth control bills have morality rates of half of those of pregnant women.
the pill can also reduce ovarian and endometrial cancers
sterilization is the permanent prevention of gamete release
in women is to tie a section of oviduct, while a
in men is tying or cutting off the vans deferens
is the termination of a pregnancy in progress
Modern Reproductive Technologies
Detecting Disorders during pregnancy
ultrasound can generate images using sound frequencies above the normal hearing range
Aminiocentesis and chorionic villus sampling are techniques where a needle is used to obtain fetal cells from fluid or tissue surround the embryo
all detectable disorders remain untreatable in the uterus
Detecting Diseases and other Disorders
Sexually Transmitted Diseases
Treating Infertility and Disorders
Infertility- an inablility to conceive offspring is common in 1 to 10 couples worldwide
reproductive technology can help with fertility problems
Hormone therapy can increase sperm/egg production
Assisted reproductive technologies involve removing eggs from hormonal stimulation and returns them into the woman's body
in in vitro fertilization oocytes are mixed with sperm from culture fishes and are implanted in the woman's uterus
intracytoplasmic sperm injection is drawn up into a needle and is injected directly into an oocyte to achieve fertilization
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