Human eggs use chemical signals to attract sperm. New research from Stockholm University, Manchester University NHS Foundation Trust and The University of Manchester shows that eggs use these chemical signals to “choose” sperm. Different women's eggs attract different men's sperm – and not necessarily their partners..
There is ample evidence to show that as millions of human sperm cells swim towards a waiting ovum or egg, only one gets to fertilize it. Now, a new study shows that even though the fastest and most capable sperms reach the ovum first, it is the egg that has the final say on which sperm fertilizes it.
Finally, the egg can affect which sperm wins the race with the chemicals it releases in the follicular fluid that surrounds the egg. That's the part which contains the chemical breadcrumbs eggs use to attract and guide sperm to their goal.
We often have heard that sperm from semen race towards the egg to enable fertilisation, with the fastest and fittest sperm winning the lottery. However, a study from 2020 highlighted that it isn't the sperm that rushes to claim its first position, it's in fact the egg that chooses which one gets to win.
Sperm cells, bacteria and other microscopic organisms use varying concentrations of chemicals in their environment – concentration gradients – to approach or avoid something in a process called chemotaxis. Egg cells release an attractant chemical, which lures the sperm.
If one egg is fertilised by two sperm, it results in three sets of chromosomes, rather than the standard two - one from the mother and two from the father. And, according to researchers, three sets of chromosomes are "typically incompatible with life and embryos do not usually survive".
Occasionally, two sperm are known to fertilize a single egg; this 'double fertilization' is thought to happen in about 1% of human conceptions. An embryo created this way doesn't usually survive, but a few cases are known to have made it — these children are chimaeras of cells with X and Y chromosomes.
The Y chromosome, which makes boys, contains less DNA than the X chromosome for girls. That means sperm that bear a Y chromosome swim faster in viscous liquids.
They are also referred to as sex cells. Female gametes are called ova or egg cells, and male gametes are called sperm.
Sperm competition results in a sexual conflict of interest between males and females. Males have evolved several defensive tactics including: mate-guarding, mating plugs, and releasing toxic seminal substances to reduce female re-mating tendencies to cope with sperm competition.
Summary: Sperm in the first fraction of ejaculate are more numerous, move more and present better quality DNA than those lagging behind.
Sexual positions
Deep penetration, for example doggy style, means the male sperm that can swim faster start their race closer to the cervix and are more likely to reach the egg first, resulting in a boy. To try and conceive a girl, Shettles suggested avoiding deep penetration, favouring the missionary position.
Even though only one sperm is needed for fertilization, most sperm cells will not survive the journey from the testicle to the uterus. Of the 200 million sperm deposited near the cervix in an average ejaculation, only 100,000 make it to the womb. For this reason, it's important to have a healthy sperm count when TTC.
Dr Michael Thomas MD (fertility specialist) actually advises that there are no methods to affect the sex of your child, including sexual position.
This produced the largest dataset available on the sex ratio throughout the stages of pregnancy. A key result from this study was that the sex ratio at conception is equal: there is no difference in the number of males and females conceived.
Shettles. The basis for the Shettles method starts with the fact that X-chromosome sperm (female) are on average slightly larger and thus slower moving than Y-chromosome sperm (male). And X-chromosome sperm live longer.
Although this is quite rare it can happen and it's called superfetation. Two babies are conceived from separate acts in two different cycles. These babies can be from the same father or two different men. When heteropaternal superfecundation occurs, the babies are from different fathers.
However, for a given pregnancy, only the mother's genetics matter. Fraternal twins happen when two eggs are simultaneously fertilized instead of just one. A father's genes can't make a woman release two eggs.
Superfecundation twins: When a woman has intercourse with two different men in a short period of time while ovulating, it's possible for both men to impregnate her separately. In this case, two different sperm impregnate two different eggs.
To form identical or monozygotic twins, one fertilised egg (ovum) splits and develops into two babies with exactly the same genetic information. To form fraternal or dizygotic twins, two eggs (ova) are fertilised by two sperm and produce two genetically unique children.
But any forensics expert will tell you that there is at least one surefire way to tell them apart: identical twins do not have matching fingerprints. Like physical appearance and personality, fingerprints are largely shaped by a persons DNA and by a variety of environmental forces.
In 99.9% of cases boy/girl twins are non-identical. However, in some extremely rare cases resulting from a genetic mutation, identical twins from an egg and sperm which began as male (XY) can develop into a male / female pair.
There is no specific frequency with which a man should ejaculate. There is no solid evidence that failure to ejaculate causes health problems. However, ejaculating frequently can reduce the man's risk of getting prostate cancer. Ejacu-lation can be through having sex or masturbating a few times a day.
The concentration of sperm is what makes the semen cloudy and thick, so if your ejaculate is watery it is possible that you have a low sperm count. This doesn't mean you're infertile (so precautions to prevent pregnancy still need to be taken for couples that don't want to get pregnant).
Knowing that sperm live for 3–5 days in the female reproductive system, for example, means you could have sex several days before your partner ovulates and still result in a pregnancy.