. In 2015, an international team of scientists assembledthe complete genome sequences of two differentwoolly mammoths. Both specimens were discoveredburied in the permafrost of Siberia, the coldest inhabited place on earth. Through radiocarbon dating, itwas determined that one of the mammoths, found onWrangel Island off the Siberian coast, died about4000 years ago; the other mammoth, found in thetown of Oimyakon, died about 45,000 years ago.Analysis revealed that the genome sequences ofthese two animals differed significantly in the distribution of base pairs at which they are either homozygous or heterozygous. The Wrangel Island woollymammoth had an extreme excess of runs of homozygosity (ROHs), regions in which the animal was homozygous for all of the base pairs. About 23.4% ofthe Wrangel Island animal’s genome was composed ofROHs that were greater than 500 kb in length; someof these ROHs were in excess of 5 Mb long. In contrast, only 0.83% of the Oimyakon animal’s genomeconsisted of ROHs longer than 500 kb.a. Explain how polymorphisms are detected when sequencing a genome. How would researchers know,for any particular base pair, whether a genome ishomozygous or heterozygous?b. What does the extreme excess of ROHs in theWrangel Island mammoth genome suggest aboutthat animal’s parents?c. The Wrangel Island woolly mammoth is thought tohave belonged to the last population on earth before the species went extinct about 4000 years ago.The answer to part (b) suggests one possible reasonfor the woolly mammoth’s extinction. Explain.
. In 2015, an international team of scientists assembled
the complete genome sequences of two different
woolly mammoths. Both specimens were discovered
buried in the permafrost of Siberia, the coldest inhabited place on earth. Through radiocarbon dating, it
was determined that one of the mammoths, found on
Wrangel Island off the Siberian coast, died about
4000 years ago; the other mammoth, found in the
town of Oimyakon, died about 45,000 years ago.
Analysis revealed that the genome sequences of
these two animals differed significantly in the distribution of base pairs at which they are either homozygous or heterozygous. The Wrangel Island woolly
mammoth had an extreme excess of runs of homozygosity (ROHs), regions in which the animal was homozygous for all of the base pairs. About 23.4% of
the Wrangel Island animal’s genome was composed of
ROHs that were greater than 500 kb in length; some
of these ROHs were in excess of 5 Mb long. In contrast, only 0.83% of the Oimyakon animal’s genome
consisted of ROHs longer than 500 kb.
a. Explain how polymorphisms are detected when sequencing a genome. How would researchers know,
for any particular base pair, whether a genome is
homozygous or heterozygous?
b. What does the extreme excess of ROHs in the
Wrangel Island mammoth genome suggest about
that animal’s parents?
c. The Wrangel Island woolly mammoth is thought to
have belonged to the last population on earth before the species went extinct about 4000 years ago.
The answer to part (b) suggests one possible reason
for the woolly mammoth’s extinction. Explain.
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