Discussion of everything related to the Theory of Evolution.
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There are a few things I am trying to ensure I understand correctly so wanted to ask a few questions.
I read that species which are closely related can impregnate each other but the viability of the pregnancy depends on how similar their DNA is. I also read that when the species are too disimilar the sperm will not be able to fertilise the egg at all.
If I recall there is something which prevents the sperm from reaching the important part of the egg in order to initialise the fertilisation. My questions are
A: What is this barrier
B: How does it identify the fact that the DNA within the sperm is too disimilar?
2: Combination of male/female DNA
If I recall correctly my sperm has a full double-helix copy of my DNA. I believe I read that upon fertilisation the DNA from the make and the DNA from the female splits along its length and attempts to connect to the half of the partner's DNA. Is that correct so far?
I think I also read that the DNA breaks up into smaller pieces and basically floats around until it finds a site on the target DNA to which it can connect strongly (where most nucleotides match their complementary nucleotide in the partner's DNA.) Is that also correct? If so then is it only the male/male DNA that gets split up? If both get split up then how to they reassemble into the correct order?
If this is all wrong then an explanation would be appreciated, or a plan-English link
3: Endogenous retro viruses
I've read about retro viruses becoming endogenous and then becoming common enough to exist in two or more species (humans/chimps for example.)
My question is, should I expect to see some of these ERVs in only some groups of human/chimp? It doesn't make sense to me that they would be in ALL humans/chimps unless there was a point where there was a massive population bottleneck.
Thanks for your time!
2: completely wrong. The DNA keeps the hereditary information, so it MUST stay intact and correct at all costs and times! If not, that can lead e.g. to cellular death, cancer or other serious stuff.
However, the homologous chromosomes are paired during the meiosis.
Cis or trans? That's what matters.
1: Zona pellucida is the gelatinous extracellular matrix that surrounds the egg, that the sperm has to encounter. The zona pellucida contains 3 glycoproteins, ZP1,2,and 3, which are important in the recognition of the sperm. ZP3's sugar molecules are recognized and bound by a GalT that is on the sperm's surface membrane, which then produces the acrosomal reaction. The binding of these sugar molecules to the beta-1,4-galactosyltransferase-I is species specific. Hopefully the DNA of the organism that made the sperm has produced the right GalT enzyme to recognize the specific sugar molecules of the egg's zona pellucida.
2. is completely wrong as pointed out.
hmm you have mixed up a few ideas.
what happens during fertilisation is that the females DNA gets ligned up with the males. so end result we will have 46 DNA moecules. all of them undergo replication as a result we get 92 DNA moecules = 46 chromosomes or 96 chromatids.
now what can happen is that the DNA 1 one of the man will have formed a chromosome. similarly even for the female.
now a part of the chromosomes MAY get cut off and exchanged. this is called crossing over.
hmm i dont know how much this would help
i guess i may have confused you. though if you dont understand get back. i will try harder
it isn't what you do that matters but it is how you do it
Recognition of Egg and Sperm
I think you are confused here.
Each of your body cells has two copies of each chromosome - except if you are male the X and Y make up the sex chromosome pair.
When sperm and eggs are created they end up with only one set of chromosomes.
When egg and sperm come together in fertililization there are again two sets of chromosomes.
You are probably thinking about the production of eggs and sperm where the chromosomes line up as pairs and parts are exchanged between the two chromosomes. Look up recombination and meiosis.
AFAIK the double helix only zips open when it is being 'read' to make the proteins.
I should dig out "The language of the Genes" and re-read it. There was a section which (if I recall correctly) talked about how two halves of the helix split apart and then recombine.
Could anyone recommend any videos, maybe on youtube?
Thanks very much!
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