2007-02-15 00:37:01 · 7 answers · asked by hedZy ♀ The Dancing Banana 4 in Science & Mathematics ➔ Biology
That depends on the genetic system of a taxon. In mammals including humans, there are sex chromosomes.
Each gamete (reproductive cell) has one sex chromosome, either X or Y (their names allude to their shape). At fertilization the male and female gametes fuse, a pair of sex chromosomes is constituted, and in that moment the sex of the embryo is determined: XX --> female, XY--> male.
Birds have a similar system, but with ZW --> females and ZZ --> males (some insects are like this too).
In contrast, the sex of 'reptiles' is determined by incubation temperatures. Other animals have different systems for sex determination.
2007-02-15 00:49:07 · answer #1 · answered by Calimecita 7 · 6⤊ 0⤋
In mammals sex is determined at conception. The embryo's sex is determined by whether the sperm is carrying the X chromosome or the Y chromosome. The eggs are all X. If an egg is fertilized by an X carrying sperm, the embryo will be female. If it's fertilized by a Y carrying sperm, the embryo will be male.
Sex determination in birds, reptiles, worms and probably alot of other things is different than for mammals.
2007-02-18 15:15:02 · answer #2 · answered by BP 7 · 0⤊ 0⤋
The second the sperm penetrates the egg is when the embryo's sex is determined. All of the sperm contain a sex chromosome - either a Y chromosome or an X chromosome. If one with a Y fertilizes the egg, the embryo will be a boy. However, we won't necessarily see visible sex differences for weeks or months when the sex differentiation occurs.
edit - This is referring to humans!
2007-02-15 00:48:12 · answer #3 · answered by Julie K 3 · 0⤊ 0⤋
As soon as a sperm penetrates the egg. The egg will always be 'female' (X), but a males sperm are either 'female' (X) and 'Male' (Y). So if a X sperm penetrates the egg the first embryo will be female - XX, and if a Y sperm penetrates it first it will be Male -XY. So males will always determine the sex of an embryo. Did you know that humans 'make' more males babies, but male babies have a higher mortality so it evens out. More male embryos and babies, but more of them die than female embryos and babies.
2007-02-15 00:49:43 · answer #4 · answered by Charlie 1 · 0⤊ 0⤋
In mammals sex is determined at fertilization. The male gamete (sperm) carries either a male or female chromosome (y or x in humans) which, when it unites with the female gamete (egg) will determine the sex.
In reptiles, fish, and plants a whole different set of rules apply...
2007-02-15 00:47:33 · answer #5 · answered by Anonymous · 2⤊ 0⤋
At some stage the ultrasound image could show a protrusion that might be a penis - a definite boy sign. On the other hand it might not show one because of the angle of the embryo with respect to the scanner or it might show some other thing (like a part of the cord or some other temporarily-enlarge part ) that is mistaken for a penis.
The longer you wait the easier it is to tell.
2007-02-15 00:44:18 · answer #6 · answered by Rich Z 7 · 0⤊ 3⤋
God determines it before conception ever even occurs...remember?
2007-02-15 00:44:48 · answer #7 · answered by Anonymous · 0⤊ 3⤋