How are rungs added to DNA through evolution? Wouldn't you need the same mutation for both male and female?

Question

All organisms don't have the same number of rungs in their DNA. If they all evolved from the same source, how are the rungs added? During reproduction, one side of the DNA comes from the male and the other from the female (at least for the more advanced organisms). Wouldn't you need the same mutation on both sides for it to be passed down to the next generation?

The answers so far don't seem to comprehend that it takes two sets of DNA for reproduction. They zipper together to make the entire DNA strand. You can have mutations on either strand or add a rung. For the mutation to be passed down -- does it have to be on both sides --- stop reciting and think about this for a minute before replying

I'm referring to adding rungs not mutations on existing rungs

I never said I was an expert on this stuff, that's why I'm asking questions. Some of the answers are demeaning --- looks like evolution still has a ways to go when it comes to our level of civilization

Answer 1

Your question is actually asking about two different things: evolution and DNA replication.

DNA replication is the process by which DNA is copied so that it can be passed on to daughter cells: a cell divides into two daughters, and as a part of the process it makes two copies of its DNA - where there was only one - so that each cell can have its own full copy of all the genes. The process is very complicated and is organized so that mutations are repaired before they are transmitted to the daughters. No process is perfect, though, and so mutations sometimes arise and are not repaired.

Mutations can be of several types: missense (resulting in the replacement of an amino acid with a different one), nonsense (resulting in a shortened protein), or alteration of the number of basepairs (i.e. 'rungs') in the DNA molecule (insertions add bases, deletions remove bases, indels insert new bases where others were deleted). On a larger scale, whole genes or even larger segments of chromosomes can be inserted or deleted. These events are rare, but happen often enough so that they can be observed.

This can happen in cell division in the cells of your body, called somatic mutation, or in the cells that give rise to your gametes (egg and sperm cells), called germline mutation. When the mutations are 'somatic' they affect only the daughter cells and are not passed on to any offspring you may have later. For example, someone may have childhood leukemia (due to mutations in the blood producing cells of the bone marrow) and survive to have their own healthy children because their gametes were unaffected by the somatic mutations that caused the cancer.

Alternately, if mutations arise in the germline, these can be passed on to later generations. The red/green colorblindness that some men have is an example of this: a mutation may occur in the mother's germline cells as the DNA is replicated and so some of the eggs that are made are missing the gene that allows one to see the color green. If a boy is conceived with one of those eggs, then they never have the appropriate gene and so can never properly discriminate between shades of red and green.

I brought up this example because it suits your question: the mother can have a proper arrangement of 'red' and 'green' genes, but occasionally - by a process known as 'unequal crossing over' - she can lose the 'green' gene on one of her X chromosomes. Thus, her two X chromosomes end up having different numbers of basepairs and different numbers of genes, but she is still able to have children - it is just that half her boys will be red/green colorblind.

As I mentioned above, these events are rare, but not too rare: for the most part, we all have the same set of genes (although males have the additional genes of the Y chromosome), but our genes vary in their sequences. That is, mutations have occured during the formation of the gametes of our ancestors. Thus, although we all have the same set of genes, we are all quite different from each other both externally (i.e. appearance) and internally (i.e. physiology, responses to medicines, etc.) because our genes not exact copies of each other, but are variable sequences of basepairs. And these variations arose because the DNA replication was not quite perfect.

Over vast amounts of time - and vast numbers of cell divisions and generations of parents and offspring - these variations can contribute to the formation of new species. That is how DNA replication is related to evolution. But, as noted by the other answerers, the premise that the DNA of both parents must have exactly the same number of 'rungs' is not correct.

I hope this makes sense, but it is awfully complex to try to sort it out in a short answer format like this. If you are really interested, a high school general biology book would probably cover the basics clearly.

Answer 2

It is true that you need one piece of DNA from each parent ... that piece of DNA is called a 'chromosome.'

But a chromosome is NOT an unzippered piece of DNA. The male and female DNA do NOT "zipper together to make the entire DNA strand". That is NOT how sexual reproduction works.

A chromosome is an intact (fully zippered) piece of DNA. The corresponding male and female chromosomes can have different number of rungs without any problem. Most of the rungs (actually called 'base-pairs') are actually ignored anyway (called 'junk DNA'). A surprisingly small percentage of these are actual genes.

And so NO, you do not need the same mutation in both the male and female chromosome.

As a trivial example, every boy is XY. The X and Y chromosomes are corresponding chromosomes ... one from the mother the other from the father. They do NOT zipper together. And the X and Y chromosomes are *quite* different and have a very different number of rungs.

Seriously, zefram. Your last questions indicate that you have *just* enough biological knowledge to be dangerous. Could it be that the reason you don't accept evolution is because you don't quite understand it?

---- { edit} ----

I hope my answer was not construed as demeaning. I was indeed reacting to the wording "The answers so far don't seem to comprehend that it takes two sets of DNA for reproduction. They zipper together to make the entire DNA strand." I believe all the answerers here DO comprehend that the first sentence is true and the second sentence is false ... but that you seemed quite confident of both.

I was also reacting to this and several previous questions that seem to be not asking a question, but making an argument against evolution based on faulty understanding of biology. Some of us are very testy about this because it is extremely common in this Biology forum.

My apologies if you are asking genuine questions, rather than just asking rhetorical questions to attack evolution. Genuine questions are *great*! That's how we all learn.

Answer 3

The mutations would be passed from cell to cell via DNA replication. If the mutation is passed through to the next generation via reproduction, the offspring would be carriers of the mutation. Move it down some generations and if a make and female who are both carriers of the mutation (having that same common ancestor where the mutation began) some of their offspring may have the mutation on both chromosomes. If this mutation become advantageous for survival or reproduction, those who have it will produce more offspring than those who don't and the percentage of those with the mutation will increase. This can eventually be part of the entire population.

Answer 4

Your terminology is vague. I'm going to assume that "rung" means base pair. On of the major factors in evolution is gene duplication. These random events add functional copies of genes. If the extra gene creates a survival advantage, over many generations, the extra gene will become the predominant allele. The X and Y chromosomes are not balanced. The Y chromosome carries a small set of genes. The X chromosome carries the complements to many of the genes that do not determine male sex. Lastly, there are chromosomal events known as balance translocations.

Answer 5

There are different types of mutations. Chromosomal mutation and gene mutation. I hope you know what i mean.
Well
1+1=2
2+2=4
1+2=3 and not immposible.
Even if it is from one side of parent's, A difference in genetic information brings diffrence in the Phenotype (or genotype incase of reccesive genes) of an offspring. So the argument is the offspring will belong, Most likely, to different species, hence might lack a partner to reproduce with i.e to have another fertile offspring) What do you think?

Answer 6

Holy moley. Where do you start? Your question indicates a remarkable lack of knowledge of basic biology. Were you paying attention in school or did you learn it all at church.