Originally Posted by Michael
I'll help you with the medical aspect of this question but not trangress the Islamic aspect of this..
first let's go over a few terms
Autosomal dominant-- is one of several ways that a trait or disorder can be passed down through families. If a disease is autosomal dominant, it means you only need to get the abnormal gene from one parent in order for you to inherit the disease. One of the parents may often have the disease.
Autosomal Recessive-- individuals who have received two copies of an autosomal gene, one copy from each parent. The gene is on an autosome, a nonsex chromosome. The parents are carriers who have only one copy of the gene and do not exhibit the trait because the gene is recessive to its normal counterpart gene.
If both parents are carriers, there is a 25% chance of a child inheriting both abnormal genes and, consequently, developing the disease
Mitochondrial inheritance: The inheritance of a trait encoded in the mitochondrial genome. Because of the oddities of mitochondria, mitochondrial inheritance does not obey the classic rules of genetics. Persons with a mitochondrial disease may be male or female but they are always related in the maternal line and no male with the disease can transmit it to his children.
X-linked dominant-- is mode of inheritance in which a gene on the X chromosome is dominant. Females can be more frequently affected than males since they have two X chromosomes that could potentially carry the abnormal gene, whereas a male has only one. However, the Lyon hypothesis states that X-inactivation renders only one copy of the X chromosome active in each cell hence on average one would expect only one half of the cells to express the abnormal gene. The chance of passing on an X-linked dominant disorder differs between men and women.
X-linked recessive is a mode of inheritance in which a mutation in a gene on the X chromosome causes the phenotype to be expressed only (1) in males (who are necessarily hemizygous for the gene mutation because they have only one X chromosome) and (2) in females who are homozygous for the gene mutation (i.e., they have a copy of the gene mutation on each of their two X chromosomes).
X-linked inheritance-- means that the gene causing the trait or the disorder is located on the X chromosome. Females have two X chromosomes, while males have one X and one Y chromosome. Carrier females who have only one copy of the mutation do not usually express the phenotype, although differences in X chromosome inactivation can lead to varying degrees of clinical expression in carrier females since some cells will express one X allele and some will express the other
just a brief summary of how some traits and/or disorders are passed down.. there is also such thing as
Penetrance - the frequency of expression of an allele when it is present in the genotype of the organism (if 9/10 of individuals carrying an allele express the trait, the trait is said to be 90% penetrant)
Not all phenotypes that are expressed are manifested to the same degree. For polydactyly, an extra digit may occur on one or more appendages, and the digit can be full size or just a stub. Therefore, when the P allele is present it expresses variable expressivity.
Expressivity - variation in allelic expression when the allele is penetrant.
why am I giving you a brief analysis of all of this? It is simple, though we might know the science behind these phenomenon we can only PREDICT the chances of something happening but not whether or not it will actually happen-- for instance and please pay special attention because this is where your answer lies, and we'll go to what we actually know beyond expressivity and Penetrance which in and of itself is in the realm of the almighty . Say you know a lady who has cystic fibrosis, cystic fibrosis is an autosomal recessive trait, she marries a man who also carries this trait what are the chances they will have a child with that trait? will you can draw your Punnett square and your answer will be very apparent...say this couple has 4 children with cystic fibrosis, does that mean it is an Autosomal dominant trait and will affect every child? absolutely not. we can't predict who will be affected we can only use the terms when counseling such patients, you'll have a 25% chance with eery pregnancy of having a child with cystic fibrosis...
let's use another example-- say you have a coin with two sides heads and tails. there will always be a 50% chance when you flip a coin that it will be heads or tails correct? say I pick tails and the first 898 times you tossed it always landed on heads, does that mean my chances of having heads the next time you toss that coin is 100% guaranteed heads given your previous 898 attempts? absolutely not the chances don't change they will always be 50/50.. you can't predict in a toss which side it will land on, but it is a guarantee it will be one or the other..I hope you understand what I mean by this insha'Allah and hope it answers your question... science can't predict and tell you 100% fool proof when you've sex on a Monday you'll be guaranteed a male child.. this is simply beyond the realm of science.. they can tell you, there is a chance of male/female, there is no chance of fertility at all, there is a chance your child might end up with this 75% guarantee or 25% guarantee, there is a chance your child will be born with a disomy, a trisomy, might end up a hydatid mole, there is a chance it will look like you, like the mother or like the paternal uncle, they can't tell you which genes are going to combine in what sort of combination to predict the final phenotype of your conception-- .. since it is all a matter of the almighty...
sperms don't have just the assigned role we tend to think of them, which is to swim and fertalize, there is a whole life going on there, some sperms play guard to prevent other sperms from passing through, there is behavioral and chemical tactics to this microscopic cells, each having assigned roles that are beyond the purposes of this discussion here and go well beyond the reason for the question, and the same goes for eggs by the way.. so it could very well be certain maneuvers predict a particular outcome.. we can't tell since we haven't run a study to see what sort of genes mix on what pattern to form what, under some circumstances, and I don't see couples volunteering themselves to such a study... bottom line is 'genetics' has no way to invalidate the hadith..
Allah knows best.. this is my knowledge based on science not Islamic jurisprudence and pray that it was of help to you insha'Allah?