Evolution__3rd_Edition

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Study and review questions
1 (a) How can we estimate the date when a gene
duplicated? (b) What evolutionary events are thought to
be associated with major rounds of gene duplication?
2 Some genes are present in the genomes of bacteria
and of humans, but not in the genomes of worms and
fruitflies. What are the two main hypotheses to explain
this observation, and how could they be tested between?
CHAPTER 19 / Evolutionary Genomics 571
chromosome evolution in human history, see Burt et al. (1999). In addition to the
work of Lahn & Page (1999) that we looked at in the text, several other hypotheses have
been posed specifically about sex chromosomal genomics. Ohno (1970) put forward
his hypothesis of the evolutionary conservation of the X chromosome (in mammals):
that genes will move on and off the X chromosome less than for autosomes, because of
the peculiar gene regulatory difficulties. Lahn & Page (1999) might lead to a fourfold
complication of Ohno’s hypothesis. Other classic material is covered in White (1973).
In the evolution of repetitive DNA, a further topic is “concerted evolution.” Elder &
Turner (1995) is a review.
3 In the human genome, pairs of genes on the X
and Y chromosomes fall into four regions down the
chromosome, according to the sequence similarity of
the genes in the pair. The same is not true for pairs
of genes on pairs of autosomes. Why is there this
difference between sex chromosomes and
autosomes?