Many that lager yeast was different from other

Many
types of beer exist, but the majority can be put into one of the two categories
ale and lager, reflected on the type of yeast used. The ale type is made
fermentation happens on the temperature from twenty to twenty-five degrees
Celsius by using “top-fermenting” and has a low aging cycle. The lager, on the
other hand, happens on the temperature from eight to fifteen degrees Celsius by
using “bottom-fermenting” and has a long aging cycle. More on that later.

From the very beginning of brewing history, it was known
that lager yeast was different from other types. The first noticeable thing was
that brewing yeast strains did not produce any meiotic offspring. Today, we
have learned that a hybrid was formed from S.
cerevisiae and is now closely related Saccharomyces
species. Of all the genes researched, two of them appeared almost exclusively
of which one invariably showed a restriction and hybridization pattern
identical to that found in the corresponding S. cerevisiae gene, while the
other showed diversity. The finding of these two genes suggests that lager
yeast contains two types of chromosomes Sc- and Non-Sc-. The chromosomes
derived from lager brewing yeast fell in one of the three categories homologous
— two chromosomes, one of paternal
origin, the other of maternal origin — chromosomes, which recombined normally
with S. cerevisiae chromosomes, homoeologous–same genetic constitution– chromosomes,
which rarely recombined with S. cerevisiae chromosomes, and mosaic –many
different combinations– chromosomes that were composed of homologous and
homoeologous segments.

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The hybrid nature of lager brewing yeast has also been
confirmed by hybridization of radioactive probes to chromosome-sized DNA
separated by pulsed-field electrophoresis (Casey 1986b; Tamai et al. 1998;
Yamagishi and Ogata 1999). Experiments indicated at an early point that the
lager brewing yeast Sc-type of any given gene is identical to the corresponding
S. cerevisiae gene (Holmberg 1982; Nilsson-Tillgren et al. 1986; Petersen et
al. 1987). The complicated genetic nature of lager brewing yeast makes it
difficult to the breeding process. The deficiency in production of offspring would
seem to destroy classical breeding efforts. However, in the early 1980s, a
method to select for the few viable spores formed by lager brewing yeast and to
reconstruct functional brewing yeast from such offspring was devised (Gjermansen
and Sigsgaard 1981). Such spores could be used to form a heterogeneous
population for potential brewing strains, but these strains (Johannesen and
Hansen 2002; Hansen et al. 2002; Hansen and Kielland-Brandt 1996, 1996b;
Nilsson-Tillgren et al. 1986; Petersen et al. 1987) could be used for the
selection of recessive mutants (Gjermansen 1983). Out of many, none of the
techniques of analyzing genomes has been found, however times are changing.
With a rapid increase in DNA sequencing technology, such projects are now
achievable. The whole genome sequence of one strain of lager brewing yeast has
been obtained. A combination of different kinds of sequencing were used to
perform a total of 348,001 sequence reads of the genome of lager brewing yeast.
This sequence also consists of 160 million base pair of DNA. The sequences were
assembled into contigs. It was found that lager brewing yeast’s genome was 23.2
million base pairs, which is twice the size of S. cerevisiae genome
(Saccharomyces Genome Database; SGD). Contigs are classified into two groups those
with DNA and those with identities around 85%. It is now evident that two yeast
species came together to make a lager brewing yeast hybrid. One of these ORFs
(Open Reading Frame) has reported a gene consisting of a specific fructose
(Gonçalves et al. 2000). Fructose transport is one of the markers tha
distinguish S. pastorianus and S. bayanus from other Sacchromyces sensu stricto
species (Rodrigues de Sousa et al.

1995). S. bayanus is
generally isolated from oenological environments, rich in fructose. Although
this sugar does not play a major role in brewing, the gene for has stayed
around in the lager brewing yeast. In contrast to the protein-encoding regions,
the non-Sc-type intergenic regionsin the lager brewing yeast are diverged from
the Sc-type. In fact, such differential expression of homoeologues in lager
brewing yeast has been reported for the BAP2 gene (encoding a branchedchain
amino acid permease) homoeologues (Kodama et al. 2001), and for MET2 (encoding
homoserine O-acetyl transferase) and MET14 (encoding adenosylphosphosulphate
kinase) (Johannesen and Hansen 2002). “These findings tell us that the