1. Ch5_Oct_19_posted - 10/18/09...

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Unformatted text preview: 10/18/09 Transmission
of
alleles
 2
genes

each
located
on
a
different
chromosome
 A1 A2 • 4
different
allelic
combina<ons
 • independent
assortment
generates
 these
 B1 B2 •  What
are
the
genotypes
of
the
gametes
this
individual
can
produce?
 Transmission
of
alleles
 •  What
about
the
following
cross,
involving
2
different
genes,
located
on
the
 same
chromosome?
 A1 A2 B1 B2 1 10/18/09 Transmission
of
alleles
 •  What
about
the
following
cross,
involving
2
different
genes,
located
on
the
same
 chromosome?
 A1 A2 •  Genes
found
on
same
chromosome
=
LINKAGE
 (not
same
as
sex‐linkage
[means
that
gene
is
on
 X‐chromosome])
 B1 B2 •  New
nota<on
for
linked
genes
 • A1B1/A2B2
 • “/”
indicates
alleles
on
homologous
 chromosomes
 •  What
are
the
genotypes
of
the
gametes
this
individual
can
produce?
 Linked
Genes
 •  Genes
on
different
chromosomes
=
UNLINKED
 •  Alleles
of
unlinked
genes

independently
assort
 •  Genes
on
same
chromosome
=
LINKED
=
syntenic
 •  Alleles
of
linked
genes

independently
assort??
 •  Alleles
of
linked
genes

transmiVed
to
gametes
together
(co‐ segregate)?
 2 10/18/09 Sex‐Linked
Genes
 •  Gene
is
located
on
the
sex
chromosomes
 •  Females
homozygous
or
heterozygous
for
X‐linked
genes;
 •  Males
are
hemizygous
for
X‐linked
genes
 
 
SEX‐LINKED
GENES
vs.
LINKED
GENES
 Linked
Genes
 •  What
about
the
following
cross,
involving
2
different
genes,
located
on
the
 same
chromosome?
 Individual
1
 A 1B 1 A1 A2 Only
2
types
of
gametes?
 It
depends…
 B1 B2 A 2B 2 •  Genes
found
on
same
chromosome
=
LINKAGE
 3 10/18/09 Linked
Genes
 •  Will
genes
undergo
independent
assortment
if
they
are
on
the
same
 chromosome
(i.e.,
they
are
linked)?
 Informa<ve
individual
 Must
be
heterozygous
 Non‐informa<ve
individual
 Linked
Genes
 •  Genes
found
on
same
chromosome
=
LINKAGE
 4 10/18/09 Linked
Genes
 •  Two
X‐linked
traits:
 From
Mom…
 From
Dad…
 Recombina<on
of
Linked
Genes
 •  Further
apart
genes
are
on
same
chromosome
–
experience
 more
recombina<on
 •  Genes
closer
together
–
experience
less
recombina<on
 •  Use
this
to
map
genes
on
a
chromosome!
 5 10/18/09 Linked
Genes
 Linked genes •  Alleles
of
syntenic
(linked)
genes
 transmiVed
to
gametes
together.
 •  Get
only
2
of
the
4
possible
allele
 combina<ons
in
gametes.
 •  X.O.
breaking
up
gene<c
linkage.
 •  Get
all
4
possible
combina<ons
of
 the
alleles
of
the
2
genes
in
 gametes.

 Recombina<on
Frequency
 Recombina<on
 frequency
(Rf)
 =
 •  Further
apart
genes
are

more
recombina<on
 •  1
cen<Morgan
(cM)
=
1
map
unit
(m.u.)

 •  1
cM
=
physical
distance
produces
1
%
 recombinant
offspring
 Parental chromosome Parental chromosome 6 10/18/09 Gene<c
Maps
&
Recombina<on
Frequency
 •  1
cen<Morgan
(cM)
=
1
map
unit
(m.u.)

 •  1
map
unit
=
physical
distance
produces
1
%
recombinant
offspring
 •  If
have
3
or
more
genes
can
produce
a
gene<c
map
with
their
rela<ve
 loca<ons.
 260
km
 Toronto
 540
km
 Toronto
 Montreal
 Kingston
 Gene<c
Maps
&
Recombina<on
Frequency
 •  1
cen<Morgan
(cM)
=
1
map
unit
(m.u.)

 •  1
map
unit
=
physical
distance
produces
1
%
recombinant
offspring
 •  If
have
3
or
more
genes
can
produce
a
gene<c
map
with
their
rela<ve
loca<ons.
 7 10/18/09 Linked
Genes
 Linked
Genes
happen
to
autosomes
too…
 8 10/18/09 Linked
Genes
 • Frequency
of
recombina<on
is
independent
of
allelic
arrangement.
 Genes
assor<ng
independently?
 • Use
chi‐square
test
(p128‐129)
 9 ...
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