If chromosones are altered or absent before conception what will be the result? Will conception take place?

Question

My question is really to determine if life, however viable, will occur if either the ova or the sperm has any variation of chromosonal defects? What if profound chromosonal abnormalities or absences thereof exist? Will conception take place?

Answer 1

It seems that conception often takes place with many chromosomal abnormalities, and even pregnancy, but such pregnancies seldom result in births, with a few notable exceptions.

Studies suggest that approximately 25% of all pregnancies result in a miscarriage - most before the mother is even aware that she is pregnant in the first place. Genetic problems in an embryo are 95% likely to result in a miscarriage, and are easily by themselves the largest cause of these spontaneous abortions.

Some chromosomal abnormalities are carried to term, however. Down's Syndrome and Kleinfelter's Syndrome just to name a few. Nor do these necessarily cause profound physical effects - many women with an extra X chromosome are completely unaware of it.

Answer 2

This is a really tough question to answer. It has nothing in particular to chromosome defect, and is more specific to which chromosome and where. There are defects that could be lethal (but this can happen even if genes are crossed and split in poor places during metaphase), and there are defects that can cause funky issues (like a man who is genetically a XX) or it could just mean that you have red hair instead of brown.

So, the issue is that it is very important to figure out what defect specifically you're talking about. If you are completely red/green colorblind and you're a man, then you have (at least) one defect on your X chromosome (that code for red and green receptors). There is also blue colorblindness, which means you would have at least one defect on "chromosome 2" (that codes for blue).

If you have a daughter with a woman who carries the X linked GREEN/RED colorblind gene on *one* X chromosome, (and here assume that by perfect mixing of XY and XX, you have four children in perfect ratio) your 2 daughters would both be carriers, you would have a colorblind son and a son with no problems. For basic situations like this, you can use a punnett square to figure out the odds.

Some crosses in nature (an example is with flies with red eyes and wrinkled wings - look it up. It's interesting, but I won't go into detail), lead to leathal combinations so often (%25 of the time) that they don't even make it to embryo stage.

In others, it is possible to be a carrier to no effect. It is still possible to pass the defect to future generations, and happens more often if the mate also has a mutation affecting the same gene.

Furthermore, there are even *MORE* cases where, depending on the severity of the mutation, different amounts of a defect or disease will be apparent. In huntingtons disease, the more repetitions of CAG (for cytosine, adenine, and guanine) a person has in the gene (which is on chromosome 4), the more profound the disease is (basically).

So there you have it. First, figure out if the trait you're looking for is sex linked or autosomal, recessive or dominant. Then, figure out if the parents, grandparents and great grandparents were carriers, or had the trait. From there, it's easier to determine what possible defects (if any) will happen. Good luck.

Answer 3

A chromosome can be missing (or in excess) in a gamete before of non-disjunction at meiosis II and (more rarely) at meiosis I. Abnormal chromosomes can also araise and they are generally due to problems at the "crossing-over" during meiosis II.
If the alteration is limited to one chromosome, fecondation canl still raise to a viable embryo, but the organism coming from it is likely to have severe defects in gorwth and development. Events of trisomy are more abundant than those of monosomy because only a few of these reach total development.
Examples of viability in spite of chromosomal defects are:
Down Syndrome (trisomy affecting the autosome chromosome 21), Turner syndrome (absence of an X chromosome) and Klinefelter syndrome (XXY syndrome)

Answer 4

It would but the fetus would have high complications. If chromosomes are missing part of its genetic structure is missing and what ever genetic material was contianed in those chromosomes will not form. i.e If the the chromosome was to form an arm, that arm would not form.

Answer 5

It will take place - but the outcome may be an unpleasant surprise.