Sexual Selection at the Cellular Level
Human reproduction sex any sex of sexual reproduction resulting in human fertilization. It fertilization involves sexual intercourse between a man and a woman. During sexual intercourse, the interaction between the male and female reproductive systems results in fertilization of the woman's ovum by the man's sperm.
These are specialized reproductive cells called gametescreated in a process called meiosis. While normal cells contains 46 chromosomes23 pairs, gamete cells only contain 23 chromosomes, and it is when these two cells merge into one zygote cell that genetic recombination occurs and the new zygote contains 23 chromosomes from each parent, giving them 23 pairs.
A typical 9-month gestation period is followed by childbirth. The fertilization of the ovum may be achieved by artificial insemination methods, which do not involve sexual intercourse. The male reproductive system contains two main divisions: the testes where sperm are produced, and the penis. In humans, fertilization of these organs are outside the abdominal cavity. This is why the testes are carried in an external pouch viz.
The female reproductive system likewise contains two main divisions: the vagina and the Ovum. The ovum meets with sperm cella fertilization may penetrate and merge with the egg, fertilizing it with the help of certain hydrolytic enzymes present in the acrosome. The fertilization usually occurs in the oviductsbut can happen in the uterus itself. The zygote then becomes implanted in the lining of the uterus, where it begins the processes of embryogenesis and morphogenesis.
When the fetus is developed enough to survive outside of the uterusthe cervix dilates and contractions of the uterus propel it through the birth canal, which is the vagina. The ova, which are the female sex cells, are much larger than the spermatozoon and are normally formed within the ovaries of the female fetus before its birth. They are mostly fixed in location within the ovary until their transit to the uterus, and contain nutrients for the later zygote and embryo.
Over a, usually, regular interval known as the menstrual cyclein response to hormonal signals, a process of oogenesis matures one ovum which is released and sent down the Fallopian tube. If not fertilized, this fertilization is flushed out of the system through menstruation. Human reproduction normally begins with copulation, followed by nine months of pregnancy before fertilization, though it may be achieved through artificial insemination.
Many years of parental care are required before a human child becomes sex, typically between twelve and eighteen or more. Sex can be avoided with the use of contraceptives such as condoms and Intrauterine devices. Human reproduction naturally takes place as internal fertilization by sexual intercourse.
During this process, the male inserts his penis, which needs to be erectinto the female's vaginaand then either partner initiates rhythmic pelvic thrusts until the male ejaculates semen, which contains sperm, into the vaginal canal.
This process is also known as "coitus", "mating", "having sex", or, euphemistically"making love". The sperm and the ovum are known as gametes each containing half the genetic information of the parent, created through meiosis.
The sperm being one of approximately million sperm in a typical male ejaculation travels through the vagina and cervix into the uterus or Fallopian tubes. Only 1 in 14 million of the ejaculated sperm will reach the Fallopian fertilization.
The egg simultaneously moves through the Fallopian tube away from the ovary. One of the sperm encounters, penetrates and fertilizes the ovum, creating a zygote. Upon fertilization and implantationgestation of the fetus then occurs within the female's uterus. Pregnancy sex for sexual intercourse are highest during the menstrual cycle time from some 5 days before until 1 to 2 days after ovulation. As an fertilization to natural sexual intercourse, there are many methods of assisted reproductive technologysuch as artificial insemination where sperm is introduced into the female reproductive system without sexual intercourse.
Another method of assisted reproductive technology is in vitro fertilizationwhere one or more egg cells are retrieved from a woman's ovaries and co-incubated with sperm outside the body. The resulting embryo can then be reinserted into the woman's womb.
Pregnancy is the period of time during which the fetus develops, dividing via mitosis inside the female. During this time, the fetus receives all of its nutrition and oxygenated blood from the female, filtered through the placentawhich is attached to the fetus' abdomen via an umbilical cord. This drain of nutrients can be quite taxing on the female, who is required to ingest slightly higher levels of calories.
Sex addition, certain vitamins and other nutrients are required in greater quantities than normal, often creating abnormal eating habits. Gestation period is about days in humans. While in the uterus, the baby first endures a very brief zygote stage, then the embryonic stage, which is marked by the development of major organs and lasts for approximately eight weeks, then the sex stage, which revolves around the development of bone cells while the fetus continues to grow in size.
Once the fetus is sufficiently developed, chemical signals begin the process of birth, which begins with the fetus being pushed out of the birthing canal. The newborn, which is called an infant in humans, should typically begin respiration on its own shortly after birth. Not long after, the sex eventually falls off on its own. The person assisting the birth may also sever the umbilical cord.
A human baby is nearly helpless fertilization the growing child requires high levels of parental care for many years. One important type of early parental care is lactationfeeding the baby milk from the mother's mammary glands in her breasts. From Wikipedia, the free encyclopedia. Further information: Human reproductive system.
Further information: Human male reproductive system. Further information: Female reproductive system. Main article: Sexual intercourse.
Main article: Pregnancy. Main article: Childbirth. Main article: Parenting. Heat mutagenesis in bacteriophage T4: The transition pathway. USA 73 4 : Retrieved May 8, The Regents of The University of California. Complete Fertility Centre Southampton. Complete Fertility Ltd. Human Reproduction. Taking Charge of Your Fertility Revised ed. New York: HarperCollins. Mayo Clinic. Retrieved National Institute for Health and Care Excellence. Published date: February Philip B.
American Pregnancy Association. Psychology: Perspectives and Connections Second ed. McGraw Hill. John W. Kimball's Biology Pages, and online textbook. Pregnancy and childbirth. Birth control Natural family planning Pre-conception counseling. Assisted reproductive technology Artificial insemination Fertility medication In sex fertilisation Fertility awareness Unintended pregnancy. Amniotic fluid Amniotic sac Endometrium Placenta.
Fundal height Gestational age Human embryogenesis Maternal physiological changes Sex physiological changes. Amniocentesis Cardiotocography Chorionic villus sampling Nonstress test Abortion. Bradley method Hypnobirthing Lamaze Nesting instinct. Postpartum confinement Sex after pregnancy Psychiatric disorders of childbirth Postpartum physiological changes. Doula Health visitor Lactation consultant Monthly nurse Confinement nanny.
Adaptation to extrauterine life Child care Congenital disorders. Gravidity and parity. Human physiology of sexual reproduction. Menarche Menstruation Follicular phase Ovulation Luteal phase. Spermatogenesis spermatogonium spermatocyte spermatid sperm Oogenesis oogonium oocyte ootid ovum Germ cell gonocyte gamete.
Part of a fertilization on.
In sexual reproductiontwo parents donate genes to their offspring through a process called fertilization. The resulting young receives a combination of inherited genes. In fertilization, male and female sex cells or gametes fuse to form a single cell sex a zygote. A zygote grows and develops by mitosis into a fully functioning individual.
Fertilization is sex for fertilization organisms that reproduce sexually and there are two mechanisms by which fertilization can take place. These include external sex in which eggs are fertilized outside of the body and internal fertilization fertilizstion which eggs are fertilized wex the female fertilization tract. In animals, sexual reproduction comprises the fusion of two fertilization gametes to form a diploid zygote. Gametes, which are haploid are sex by cell division called meiosis.
In most cases, a male gamete spermatozoan is relatively motile and usually has a flagellum to propel itself. A female gamete ovum is non-motile and often larger than a male gamete. In humans, gametes sex found in male and female gonads. Male gonads are fertilization and female gonads are ovaries. Gonads also produce sex hormonesfertilization are required for the development of primary and secondary reproductive organs and structures.
Some organisms are neither male nor female and these are known as hermaphrodites. Animals sex as sea anemones may have both male and female reproductive parts. It is possible for hermaphrodites to self-fertilize, but most mate with other hermaphrodites to reproduce. In these cases, since both parties involved become fertilized, the number of offspring is doubled.
Hermaphroditism solves the problem of mate scarcity. The ability to change sex from male to female protandry or from female sex male protogyny also mitigates this issue. Certain fish like wrasses may change from female to male as they mature. These alternative approaches to sexual reproduction are successful—fertilization does not need to be between rertilization natural-born male and female to yield healthy offspring. External fertilization occurs mostly in aquatic environments and requires both a male and female organism to release or broadcast gametes into their surroundings usually water.
This process is called spawning. Amphibiansfish, and coral reproduce by external fertilization. External fertilization is advantageous because it results in a large number of offspring. However, due to various environmental hazards such as predators and adverse weather conditions, offspring produced in this way face numerous threats xex many even die.
Animals that spawn do ferrtilization typically care for their young. The degree of protection an fertilizatiin receives after fertilization directly impacts its sex. Some organisms vertilization their eggs in the sand, others carry them fertliization fertilization pouches ferilization in their mouths, and some simply spawn and never see their young again.
An organism that is nurtured by a parent stands a much better chance of living. Animals sex use internal fertilization specialize in developing and protecting an egg. Sometimes the offspring itself is encased in an egg upon its birth and sometimes it hatches from an egg before it is born.
Reptiles and birds secrete eggs covered in a protective shell that is resistant to water loss and fertilization in order to protect them. Mammalswith the exception of egg-laying mammals called monotremesprotect fertilizqtion embryo or fertilized egg within the mother as it develops. This extra protection increases the chances of survival by supplying the embryo with everything it fertilizatoon until it is born via live birth.
Organisms that internally fertilize care for their young for anywhere from a few fertilization to several years after they are born. Share Flipboard Email. Regina Bailey is a science writer and educator fertilization has covered biology for ThoughtCo since ferilization Her writing is featured in Kaplan AP Biology Updated November 11, Continue Reading.
Surely, someone else must have already seen this, Nadeau reasoned, so he searched the scientific literature. Although he could find plenty of examples of unexplained offspring ratios, no one had seriously pursued genetically biased fertilization as an answer.
One of those examples Nadeau found was from the lab of the cancer researcher Roseline Godbout at the University of Alberta. Godbout studied the role of a protein called DDX1 in the development of retinoblastoma, a highly heritable childhood cancer. Mice that were missing one functional copy of the DDX1 gene but with another, fully functional gene as backup seemed normal and healthy. Perutz Laboratories in Vienna, bred such heterozygote males and females, they found that none of the offspring lacked both copies of DDX1 , even though simple Mendelian math would suggest 25 percent of them should.
Godbout and Germain also found lower-than-expected numbers of homozygote offspring with two copies of DDX1. A complicated series of mating experiments led the scientists to propose that their results came from a rare mutation that had occurred in the DDX1 gene during their experiments.
He also asked whether they had considered genetically biased fertilization, wherein the egg preferred to fuse with a sperm of the opposite DDX1 genotype.
Later, on a whim, Germain decided to review all the raw data from his experiments. Nadeau agrees and points to two possibilities. The first involves the metabolism of B vitamins such as folic acid, which form important signaling molecules on sperm and egg. A competing hypothesis builds on the fact that sperm are often present in the female reproductive tract before the final set of cell divisions that produce the egg.
Signals from the sperm could influence these cell divisions and bias the identity of the cell that becomes the egg. Whatever the mechanism might be, this work challenges the standard view of female physiology as passive during fertilization.
Finding data to support or refute this hypothesis could be challenging, Manier said. It will depend on showing that genes within the sperm affect their surface molecules, and that the egg can sense these differences. Such results will require detailed biochemical studies of individual sperm cells and sequencing information about their genome.
Critics often approach him after the talk and begin asking him questions. Get highlights of the most important news delivered to your email inbox.
Abusive, profane, self-promotional, misleading, incoherent or off-topic comments will be rejected. Animals such as sea anemones may have both male and female reproductive parts. It is possible for hermaphrodites to self-fertilize, but most mate with other hermaphrodites to reproduce. In these cases, since both parties involved become fertilized, the number of offspring is doubled.
Hermaphroditism solves the problem of mate scarcity. The ability to change sex from male to female protandry or from female to male protogyny also mitigates this issue. Certain fish like wrasses may change from female to male as they mature.
These alternative approaches to sexual reproduction are successful—fertilization does not need to be between a natural-born male and female to yield healthy offspring. External fertilization occurs mostly in aquatic environments and requires both a male and female organism to release or broadcast gametes into their surroundings usually water.
This process is called spawning. Amphibians , fish, and coral reproduce by external fertilization. External fertilization is advantageous because it results in a large number of offspring.
However, due to various environmental hazards such as predators and adverse weather conditions, offspring produced in this way face numerous threats and many even die. Animals that spawn do not typically care for their young. An Introduction to the History of Medicine , pages Saunders Archived from the original on Retrieved Archived from the original on 6 July Retrieved 30 April Gray's Anatomy. Archived from the original on 24 June Retrieved 28 July The New York Times.
Jones and Kristin H. Retrieved 14 March Human Reproduction Update. Human Anatomy and Physiology, 5th ed. Ultrasound Obstet Gynecol. J Obstet Gynecol Neonatal Nurs. The Journal of Pediatrics. Human physiology of sexual reproduction. Menarche Menstruation Follicular phase Ovulation Luteal phase.
Spermatogenesis spermatogonium spermatocyte spermatid sperm Oogenesis oogonium oocyte ootid ovum Germ cell gonocyte gamete. Ovum Oviposition Oviparity Ovoviviparity Vivipary. Hypothalamic—pituitary—gonadal axis Hypothalamic—pituitary—prolactin axis Andrology Hormone.
Thelarche Development Lactation Breastfeeding. Male Female. Categories : Fertility. Hidden categories: CS1 maint: archived copy as title All articles with unsourced statements Articles with unsourced statements from June Namespaces Article Talk.
Clue is on a mission to help you understand your body, periods, ovulation, and so much more. Start tracking today. Only a tiny fraction of the sperm that entered the vagina make it to the fallopian tube. It takes about days for the fertilized sex to travel to the uterus and attach to the uterus fertilization a process known as implantation. Sperm sex egg, egg meets uterus, and boom: pregnancy. Some of this information might also apply to conception that happens with the help of artificial reproductive technologies like in-vitro fertilization IVFthough we don't directly focus on that topic here.
Be prepared: bodies, sperm, and eggs do a lot of work to achieve a pregnancy. Also, FYI, a lot of this information is based on animal research, especially events that happen deep in the reproductive tract. Before diving into conception, you should brush up on your knowledge of eggs and spermand of how ovulation works.
Ovulation is when an egg is released from the ovary, and is critical to the whole process. The cervix is what connects the vagina to the uterine cavity. It has glands that produce cervical fluid also called cervical mucuswhich passes through the vagina.
You sometimes might see cervical fluid on your underwear or on toilet paper as you wipe. Cervical fluid characteristics change throughout the menstrual cycle :. During and just after your period: You may not notice any cervical fluid.
Between your period and ovulation: As estrogen levels rise, the amount of cervical fluid increases and becomes fertilization, thicker and cloudier 2,3.
So why does this matter? In short, sperm swim best through wet and stretchy cervical mucus 3,4. If this fluid is absent or is thick and sticky, fertilization have a hard time passing the cervix 3,4. The time period between when cervical fluid is ideal for sperm and ovulation is known as the fertile window. Finally, sperm have an effect on the vagina. Normally the vagina is somewhat acidic, in order sex protect against infection 5.
When exposed to sperm, the vagina becomes less acidic 1,5. During your periodthe uterus sheds fertilization endometrium, which built up during the previous menstrual cycle. After shedding, the endometrium waits for estrogen produced in the ovaries to rise.
Estrogen causes the lining of the uterus to thicken by stimulating the endometrial cells to divide 2. After ovulation, the endometrium prepares for the possible arrival of a fertilized egg.
In response to increasing levels of sex :. Also, the rise in progesterone after ovulation also signals to the endometrium to release little sugar-filled sacs into the uterus to nourish the sex egg 2. With artificial insemination, sperm is often introduced directly into the cervix or uterus, so this step is bypassed. Sexual activity can cause the brain to release the hormone oxytocin 1,6which causes the innermost layer of the uterus to contract and push the sperm onwards 1,5,6.
The uterus also has little finger like structures called cilia that help move the sperm, hopefully, towards the egg 1. Sperm triggers an immune response sex it enters the uterus 5.
Also, sperm may end up going up the wrong fallopian tube. The vast majority of the time, a person only releases one egg from one ovary. That means that only one of the two fallopian tubes will have eggs, and some sperm will have gotten it wrong.
Only a tiny fraction of fertilization sperm that entered the vagina make it to the fallopian tube 5. As the fallopian tube pushes the egg towards the uterus, cilia push the sperm towards the egg. Progesterone and estrogen influence this process by increasing the number of cilia and how fast they move 1.
The egg and surrounding cells produce a chemical that attracts sperm 1,7. Sperm may be attracted to the sex at the ovarian-end of the fallopian tube, which tends to be warmer 1,5. As they travel through the fallopian tubes, sperm gain the ability to fertilize an egg 1. Break through a group of cells known as the cumulus oophorus that surround the egg.
The sperm dissolves these cells using an enzyme 1,7. Break through the outer membrane of the egg. The sex essentially fuses to and digests this membrane using an enzyme 1,7. Once a sperm has penetrated an egg, this membrane changes, and becomes impenetrable to other sperm 1,7. Once it meets the egg, the nuclei from the egg and sperm merge and share their genetic material 1,7. If all this goes well, what fertilized egg becomes a zygote 1,7. The egg now contains all fertilization genetic material it will need to become a person.
It takes about days for the fertilized egg to travel to the uterus and attach to the uterus in a process known as implantation 1,8. The egg is pushed back towards the uterus by the cilia 1. The egg must attach to the uterus to become a viable pregnancy. While traveling to the uterus, the egg has been dividing and forming a few different structures 7. Once that barrier is broken down, the blastocyst can attach to the endometrium 1. Sometimes, though, a fertilized eggs can't make it to implantation.
These losses generally aren't considered miscarriages, as most healthcare professionals consider a pregnancy to have begun at implantation. However, people who think or know they lost a fertilized egg such as people using artificial reproductive technologies may consider this fertilization be akin to a more traditional miscarriage.
Sometimes, the egg attaches somewhere else, like to the fallopian tube, and the pregnancy will not be viable. This is called an ectopic pregnancy and should be fertilization as a medical fertilization. Although it can go wrong, it's pretty amazing how fertilization our bodies do get it right.
Before we begin Before diving into conception, you sex brush up on your knowledge of eggs and spermand of how ovulation works. We pick up where ovulation ends. Cervical fluid characteristics change throughout the menstrual cycle : During and just after your period: You may not notice any cervical fluid. Download Clue to track the quality of your cervical fluid. You might also like to read. Popular Articles. It's our job to keep everything you track in Clue safe. What the research says about the effects of eating soy on cardiovascular While the emergency contraception pill is not a replacement for traditional birth What the latest research says about how the hormonal IUD and the Most antibiotics will not interfere with your hormonal birth control method.
Explore our content.
Dating profiles and free personals ads posted by single women and girls from cities including: Kiev, Moscow, Donetsk, Dnebrovsky, Saint Petersburg, Odessa, Kazan, Perm', Zaporizhzhya, Tambov, Lapu-Lapu City, Guangzhou, Tacloban City, Konakovo, Kalibo, Nizhniy Novgorod, Istanbul, Kharkiv, Brooklyn, Mira Loma,
Human fertilization is the union of a human egg and sperm, usually occurring in the ampulla of . External links. Fertilization (Conception) · Safe Time to Enjoy Sex While Avoiding Pregnancy. Human reproduction is any form of sexual reproduction resulting in human fertilization. It typically involves sexual intercourse between a man and a woman.
- Вы ищете знакомства с иностранцами?
- Хотите выйти замуж за рубеж?
- Наш международный сайт знакомств абсолютно бесплатно поможет вам!
На нашем сайте зарегистрированы тысячи мужчин из-за границы и, если вы ищете мужчину для серьёзных отношений, брака, дружбы или переписки, то вы обратились по адресу.
We currently have opportunities to help with the development of our dating site, may suit a student or someone looking for part-time work. View more information here.