Evolution/ chromosome fusion question?

Both of those sources are saying the same thing.

What is confusing you is the word "pair". That can mean any two chromosomes. When Miller says "a pair of chromosomes fused" he just means two chromosomes (2A and 2B) out of the 24.

He does NOT mean a "homologous pair". (2A and its homolog, the other chromosome 2A in the full diploid state of the cell.)

So here's what they are both saying:

1. An early primate ancestor had 48 chromosomes (24 homologous pairs), just as modern chimps do. (So that ancestor branched into two branches ... one the ancestor of modern apes, the other the ancestor of the human line. The following steps only apply to that second branch.)

2. Meiosis produces sex cells ... egg cells and sperm cells with 24 *unpaired* chromosomes.

3. In some individual, two of these chromosomes (2A and 2B) fused ... producing an egg cell or sperm cell with 23 chromosomes instead of the normal 24. No genes were lost or damaged in this fusion ... so all the necessary genes were contained in the 23-chromosome cell.

4. That 23-chromosome sperm or egg cell fertilized with the egg or sperm cell of another normal individual (with 24 chromosomes). This would have produced an offspring with 47 chromosomes.

5. You might think that an individual with 47 chromosomes would be fatal, or at least infertile ... but that is not necessarily true. (For example modern horses have 64 chromosomes, and the wild horse has 66 chromosomes ... but they can mate and produce *fertile offspring* having 65 chromosomes.)

6. That offspring with 47 chromosomes produces egg or sperm cells with either 23 or 24 chromosomes. Thus it can mate with others that have the normal 48 chromosomes (24 pairs) and produce either new individuals with 46 or 48 chromosomes.

7. In this way, the species can continue producing more members with either 46 or 48 chromosomes, and they can continue to mate with each other without serious problems. (Again, what matters is not the *number* of chromosomes, but whether the genes on those chromosomes are all present and undamaged.)

8. However, eventually some other advantage gets associated with the 46-chromosome individuals, and the new population stabilizes on 46 chromosomes as the new norm (replacing the old 48-chromosomes).

So I hope that explains it.

Summary: The fusion happened in a *gamete* (a haploid cell).

I think that when the evolutionary "event" happened, it was probably 2 chromosomes merging. Then replication lead to the second chromosome. This is speculation, because I find it difficult to believe that both chromosomes fused at the same time. Regardless, this is considered strong evidence for evolution because all primates have 24 pairs of chromosomes, while humans have 23. Chromosome #2 is an exact match of two separate chromosomes in all other primates, giving evidence for a fusion event sometime in human evolution that combined these two chromosomes into one.

In Colin's talk he means the ape pair (as in two non homologous chromosomes) fused: 2A fused with 2b.This non homologous pair fused to form what we now call Homo chromosome 2.

We are a diploid organism so it is usual to refer to the two homologous copies of the genome in each cell as pairs of chromosomes meaning the maternal and paternal homologous copies of the genome. Human Chromosome 2 has two homologous copies in the diploid so it is just a form of speech to say pairs to indicate diploidy.

This is the confusion of using pronouns rather than writing everything out in full.

That first sperm or egg with one fused Chr 2 A/B formed a zygote with a gamete without a fused Chr 2 but with no blockage to alignment of all the pieces. Chr A/B aligned with Chr A & Chr B in metosis for the organism to grow and develop.

Possibly the cell repair mechanisms 'fixed' the unfused Chr A to Chr B at some point in the synaptic alignment for meiosis' crossover so there were two copies of the Chr A/B. This ensured the pairs separated properly to daughter cells. These gametes again merged with 'unfused' gametes and the process repeated. Once the rearranged chromosome 2 became common in the population 'fused' gametes just met other 'fused' gametes as the frequency in the population increased.

Chromosomal rearrangements occur constantly and are a major form of genetic change. This is why whole genome syntenic homology studies are so important. The degree of rearrangement says much to how divergent to two species are but also to how critical gene groupings or gene linkages are. When we see two species with many rearrangements but one group of genes kept in the same order there must be selective pressure to preserve that order.

Shared synteny

http://en.wikipedia.org/wiki/Synteny

"i think Chromosome 2 fusion is in basic terms occurred with cutting-edge human beings..." Why do you think that? Miller's element is that human beings and apes are assumed to be heavily suitable yet apes have a various chromosome sort. If we gained't discover an evidence for the version then the thought we are heavily suitable will become much less probably. He then provides an evidence. "yet, why such chromosome fusions did not take place in different primates like Bonobos, Chimpanzees, Gorillas?" A chromosome fusion ensuing in a practicable offspring is a uncommon journey. "What approximately for different Homo Species like Neanderthals, Homo Erectus? have they have been given 40 8 or 40 six? " we gained't study the genomes of those species. "Did this journey take place in one individual or concurrently in an entire inhabitants? " It initially occurred in one individual. "i'm uncertain no rely if Chromosome fusion is empirical data for a difficulty-unfastened link between Apes and human beings." The data for the relatedness of apes and human beings is the stunning similarity of our anatomy and our genome. The remark of the fusion journey provides to this line of knowledge.

Both.

One human chromosome (2) is the result of the fusion of two ancestral chromosomes which are the 2A and 2B chromosomes of chimps. The original data was in the Wikipedia references.