2006-12-22 01:53:00 · 3 answers · asked by lil l 2 in Arts & Humanities ➔ Genealogy
It depends on what your genotypes are.
If you are both + +, then ALL of your children will be + +.
If you are both + -, then your children have a 1/2 chance of being + -, a 1/4 chance of being + +, and a 1/4 chance of being - -.
If one of you is + + and the other + -, then your children have a 3/4 chance of being + + and a 1/4 chance of being + -.
There is no "maximum." You could be a + -/+ - couple and have twenty children that are - - although that is quite unlikely.
By the way, positive genotypes are considered + + and + -. The negative genotype is - -. The + gene is dominant.
2006-12-22 02:00:25 · answer #1 · answered by chad5871 2 · 1⤊ 0⤋
There is no maximum. If both parents are Rh positive and ANY child is Rh negative, then this means that probability of ANY child being Rh negative is exactly 25%. Although probability can be a difficult science to understand, please take my word for it that the chances do not change just because there are previous children - each child has precisely a 25% probability of being Rh negative, and a 75% chance of being Rh positive.
Obviously the chances OVERALL of having four Rh negative children are fairly small - 1 in 256, but if there are already 3, then the chances for the fourth child remain 1 in 4.
Incidentally, Tham's answer is incorrect. Each of us carry two copies of each gene, one inherited from our father and one from our mother. For each gene, our children will inherit only ONE of these, since they need to inherit the other half of their genes from the other parent. For ANY child of two Rh + parents to be Rh -, it means that BOTH parents must have one + gene and one - gene. Since the + gene is dominant, anyone in this situation will be Rh +, but the version of the gene they pass on can still be either of the two they carry, which in this case can be either + or -. For the child to be Rh -, both parents must pass on the - copy of the gene, and there is a 25% chance of this occurring,
2006-12-22 02:10:34 · answer #2 · answered by Graham I 6 · 2⤊ 0⤋
You are speaking about odds. There is nothing that enforces the odds of a certain event. You could flip a coin ten times with it coming up heads every time. Not probable but certainly possible.
2006-12-22 02:04:13 · answer #3 · answered by know_it_all_NOT 3 · 0⤊ 0⤋