7. Chapter_summaries_1-4_

7. Chapter_summaries_1-4_ - USE
 THE
 LEARNING
...

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Unformatted text preview: USE
 THE
 LEARNING
 GOALS
 POSTED
 IN
 THE
 LECTURE
 SECTION
 TO
 HELP
 GUIDE
 YOU
 WITH
 RESPECT
 TO
 WHAT
 YOU
ARE
EXPECTED
TO
KNOW.

 Ch1
Summary
 • This
material
was
simple
enough
that
you
should
be
able
to
provide
your
own
summary.

Making
chapter
 summaries
is
useful
and
is
good
review
of
the
materials
and
concepts
that
you’ve
studied.

 Ch
2
Summary
 • • • Remember
 there
 are
 2
 alleles
 of
 each
 gene,
 when
 describing
 the
 genotype
 of
 an
 individual.
 
 If
 you
 are
 describing
gametes,
there
is
only
1
allele
of
each
gene
per
gamete.
 Recognize
if
a
trait
is
dominant
or
recessive
by
considering
the
phenotype
of
the
F1
generation.

 Recognize
ratios:
 o Monohybrid
–
involves
1
gene
and
a
cross
between
2
individuals
heterozygous
for
that
gene.

The
 genotypic
ratio
of
the
offspring
(F2)
is
1:2:1.
(This
is
regardless
of
the
type
of
inheritance
 –
 e.g.,
 dominant/recessive,
 codominant.
 
 In
 a
 simple
 dominant/recessive
 relationship
 of
 the
 alleles
 involved
you
obtain
a
3:1

 o Dihybrid
 –
 involves
 2
 genes
 &
 a
 cross
 between
 2
 individuals
 heterozygous
 for
 both
 genes.
 This
 cross
results
in
4
genotypic
classes
(A‐B‐;
A‐bb;
aaB‐;
aabb)
in
a
9:3:3:1
ratio.
Again,
if
the
alleles
 are
in
a
dominant/recessive
relationship
then
you
will
get
a
phenotypic
ratio
of
9:3:3:1
as
well.
 A
test
cross
can
be
used
to
establish
the
genotype
of
an
individual
expressing
a
dominant
phenotype.

 Probabilities
for
all
potential
outcomes
must
add
up
to
1
 If
 2
 outcomes
 must
 occur
 together,
 the
 probability
 of
 one
 outcome
 AND
 the
 other
 occurring
 is
 the
 product
 of
 the
 2
 individual
 probabilities.
 
 (The
 final
 outcome
 is
 the
 result
 of
 two
 independent
 events.)
 (E.g.,
probability
of
getting
a
4
on
one
die
AND
a
4
on
the
second
die
is
the
product
of
the
two
individual
 probabilities.)
 If
there
is
more
than
one
way
in
which
an
outcome
can
be
produced,
the
probability
of
either
one
OR
the
 other
 occurring
 is
 the
 sum
 of
 the
 individual
 probabilities.
 
 In
 this
 case,
 the
 outcomes
 are
 mutually
 exclusive.
 Pedigrees
–
you
should
be
able
to
draw
and
interpret
pedigrees
(Fig.
2.20
&
2.21;
Table
2.2)
 Determine
 the
 gametes
 produced
 by
 the
 parents
 in
 a
 mating
 and
 the
 probabilities
 of
 the
 potential
 offspring.
 Use
 branched
 diagrams,
 or
 the
 method
 indicated
 by
 branched
 diagrams,
 which
 is
 that
 in
 a
 question
 involving
multiple
genes
you
can
look
at
each
gene
independently
and
then
multiply
all
the
probabilities
 (for
the
various
genes
involved).
 • • • • • • • Ch
3
Summary
 • Novel
phenotypes
arise
when
there
is
codominance
or
incomplete
dominance.
The
novel
phenotype
will
 appear
in
the
F1
generation.

In
the
F2
generation,
this
same
phenotype
 must
be
the
largest
component
 (i.e.,
half)
of
the
1:2:1
monohybrid
ratio.
 For
 a
 series
 of
 crosses
 involving
 different
 phenotypes
 for
 a
 certain
 trait
 (e.g.,
 coat
 colour),
 where
 each
 individual
cross
gives
a
monohybrid
ratio,
then
all
the
phenotypes
are
controlled
by
one
gene
with
many
 alleles
(an
allele
series
 –
see
Fig.
3.6).

It
is
important
in
case
such
as
this
to
write
a
dominance
hierarchy
 for
the
alleles
of
the
gene,
e.g.,
a
=
b
>
c.
Thus,
a
is
codominant
to/incompletely
dominant
to
b
and
both
a
 and
b
are
completely
dominant
to
c.
 Lethal
mutations
are
almost
always
recessive
alleles
(Fig.
3.9).
If
there’s
a
recessive
lethal
allele
present
in
 a
 cross,
 you
 can
 never
 make
 that
 allele
 homozygous.
 Therefore,
 the
 cross
 must
 have
 involved
 parents
 heterozygous
for
the
lethal
allele.

Instead
of
the
expected
1:2:1
ratio
in
the
progeny,
one
of
the
¼
classes
 (one
of
the
homozygous
classes)
is
lethal,
so
the
monohybrid
phenotypic
ratio
will
be
2/3
heterozygous
 • • • phenotype.

The
recessive
allele
may
be
pleiotropic
and
show
a
different
 dominant
phenotype
(e.g.,
Fig.
 3.9).
 Epistasis
 involves
 two
 genes.
 In
 epistasis,
 none
 of
 the
 progeny
 die.
 All
 are
 present,
 but
 instead
 of
 4
 phenotypic
classes
in
a
9:3:3:1
phenotypic
dihybrid
ratio,
 there
is
an
epistatic
variation
where
2
or
3
of
 the
genotypes
have
been
summed
together
(e.g.,
9:3:4
or
12:3:1).
 Ch
4
Summary
 • • The
purposes
of
mitosis
and
meiosis
differ
and
thus
they
have
unique
outcomes.
 Chromosome
 alignments
 differ
 between
 mitosis
 and
 meiosis
 (though
 metaphase
 II
 of
 meiosis
 is
 almost
 identical
to
metaphase
of
mitosis).
Homologous
chromosomes
line
up
at
the
metaphase
plate
(as
pairs)
in
 meiosis
I.

After
meiosis
I,
homologous
chromosomoe
pairs
are
separated
(so
alleles
become
separated).
 During
 meiosis
 II,
 chromosomes
 line
 up
 along
 the
 metaphase
 plate
 and
 sister
 chromatids
 of
 each
 chromosome
end
up
in
each
daughter
cell.

 Chromosome
 behaviour
 during
 meiosis
 explains
 (or
 provides
 the
 basis
 of)
 Mendel’s
 principles
 of
 segregation
(alleles
of
the
same
gene
segregate
 
this
is
because
of
the
separation
of
the
homologous
 chromosomes
during
meiosis
I)
and
independent
assortment
(various
combinations
of
the
alleles
of
2
or
 more
genes
located
on
different
chromosomes).
 Determining
whether
or
not
a
gene
is
sex‐linked
can
sometimes
be
difficult.

Typically,
X‐linkage
is
seen
as
 a
 clear
 phenotypic
 difference
 between
 the
 sexes
 in
 one
 generation’s
 progeny
 of
 a
 cross.
 This
 is
 NOT
 a
 difference
in
the
absolute
numbers
of
males
and
females
of
a
certain
phenotype,
but
instead
a
phenotype
 that
is
present
in
one
sex
and
totally
absent
in
the
other
sex.

This
difference
between
the
sexes
will
be
 seen
 either
in
the
F1
 or
F2
generation,
but
 not
in
both
generations
of
the
same
cross.

It
isn’t
possible
to
 make
a
definitive
conclusion
about
X‐linkage
based
 on
just
one
generation
of
a
cross
 –
you
 must
see
the
 data
from
both
the
F1
and
the
F2.
If
the
sex
difference
is
seen
in
the
F1
generation,
then
the
female
parent
 had
the
X‐linked
phenotype.
If
the
sex
difference
is
seen
in
the
F2
 generation,
then
the
male
 parent
had
 the
X‐linked
trait.

 You
 can
 tell
 whether
 nondisjunction
 occurred
 in
 meiosis
 I
 or
 meiosis
 II
 based
 on
 the
 genotype
 of
 the
 resulting
child/offspring.


 Sex
determination
in
humans
is
genetically
determined,
however,
it
is
not
like
this
for
all
organisms.
 • • • • ...
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This note was uploaded on 01/10/2010 for the course BIOLOGY biol2040 taught by Professor Tamarakelly during the Fall '09 term at York University.

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