Download Assessment Schedule 2010 AS 90459 (Biology 2.3) Describe

Assessment Schedule 2010
AS 90459 (Biology 2.3) Describe Genetic variation and change
Question
ONE
(a)
Achievement
Merit
Sufficiency: Describes any As for Achieved and
four of (a), (b), (c), (d), (e), explains two of (b), (c),
(f).
(d), (f).
Duroc : bbww
Hampshire : BBWW
F1 : BbWw
(b)
Pure breeding means that
the individual has a
homozygous geneotype /
can produce only one type
of allele
(c)
Homozygous parent can
pass on only one type of
allele (for that trait) to
its offspring (there is
NO variation in the
alleles) so offspring
have same alleles and
phenotype as parent.
BW
Bw
bW
bw
BW
BBWW
BBWw
BbWW
BbWw
Bw
BBWw
BBww
BbWw
Bbww
bW
BbWW
BbWw
bbWW
bbWw
bw
BbWw
Bbww
bbWw
bbww
Gametes correct (A):whole Punett Square correct (M)
(d)
One of bbWW; bbWw
(e)
3/16 or 3 : 15 or correct
decimal or correct %.
Both bbWW and bbWw
and no other genotype
given.
Excellence
Discusses (f); explains (b)
and (c); describes (a) and
(e).
(f)
TWO
(a)
Gives genotype as bbWW
and describes breeding
suspect pigs with recessive
genotype (bbww) pigs and
check whether offspring
have white bands or are
solid red only.
Sufficiency: Describes
mutation and one other
source of variation in (a)
and describes (b) and (c).
Describes TWO of eg

Mutation(s) in DNA
creates new alleles.

Independent assortment
of homologous
chromosomes produces
genetically varied
gametes.

Crossing over and
recombination between
non sister chromatids in
meiosis produces new
allele combinations in
As for Achieved and
explains that

Solid red offspring
indicates suspect pig
is bbWw; all white
banded offspring
indicates suspect pig
(may be) bbWW.

if any offspring do
not have white band
/ are solid red
(bbww) then adult is
heterozygous
(bbWw) and not
pure breeding for
white banded
offspring.
As for Achieved and
explains ONE of (b) of
(c).
As for Merit and includes
explanation of the need for
several breedings eg if no
solid red (bbww) pigs
occur in the large numbers
of offspring, then the
suspect pig is (almost
certainly) bbWW so pure
breeding.
Answer supported with
correct Punnet Squares of
crosses (bbWw x bbww
and bbWW x bbww) to
show the probability of
getting white banded and
solid red offspring.
As for Merit and explains
both (b) and (c)
gametes.
(b)
Mutation must occur in
gamete producing cells
[not somatic cells] for it to
enter gene pool.
If the gamete with the
mutation is fertilized
and the offspring
produced is viable, then
the mutation will enter
the gene pool of the
population.
(c)
Describes Natural selection
as causing :
Explains ONE of ;

mutations that are
helpful / favourable to
become established in
the gene pool

mutations that are
helpful / unfavourable
to not become
established in the gene
pool

Selection pressures
will cause
individuals with
favourable alleles to
survive and
reproduce (increased
fitness) so
establishing and
increasing the
frequency of these
alleles in the gene
pool.

Selection pressures
will cause
individuals with
unfavourable alleles
to not survive / have
reduced chance of
surviving (reduced
fitness) so these
alleles will not get
established in the
gene pool or be
present in low
frequencies in the
gene pool
Discussion explains the
role of NS in determining
the presence of both
favourable and
unfavourable alleles in the
gene pool linked into a
comprehensive answer.
THREE
(a)
Sufficiency : Describes
three evolutionary
processes in (a) and
describe inbreeding and its
effect on one of these
evolutionary process in (b).
Any three of :

Bottleneck effect – eg
numbers of robins were
greatly reduced so
likely loss / reduction
in allele frequency with
likele reduction in
genetic diversity.

Founder effect – eg
only 6 breeding pairs
introduced to Ulva so
alleles present in their
gene pool not liely to
be representative of the
mainland / ancestral
population so likely
reduced gentic
diversity.

Genetic drift – loss /
reduction in specific
alleles due to chance
which is likely to be
more pronounced in the
small robin population
so corresponding
[increased] loss of
genetic diversity.
As for Achieved and
explains inbreeding and
its effect on one
evolutionary process.
As for Merit and explains
the effect of inbreeding on
three evolutionary
processes linked to the
decrease of diversity in the
gene pool and the rapid
increase in frequency of
favourable alleles in the
gene pool of the robins on
Ulva island.
(b)

Mutation – changes to
genetic code creating
new alleles. If
occurring in gamete
producing cells will
enter gene pool as
inherited.

Natural selection –
changes in the
environment cause
change in selection
pressures on robins so
favourable alleles will
be selected for and
increase in frequency in
gene pool.
Describes inbreeding eg
Explains inbreeding eg


the breeding of closely
related individuals eg
siblings, children to
parents; grand children
to grandparents in the
robin population.
and its effect on one
evolutionary process eg


Inbreeding in the small
robin population is
likely to further reduce
the genetic diversity of
the population that has
occurred in bottleneck
effect / founder effect /
genetic drift
The small size of the
population increases
the occurrence of
inbreeding occurring
by chance so that
the degree of
relatedness between
all members of the
population is high.
This increases the
chances of harmful
recessive alleles
coming together in
any individual so
reducing its fitness.
and explains its effect
on one evolutionary
process eg
Mutations that are
favourable will become 
established / increase in
Inbreeding will
reduce the genetic
Explains inbreeding and its
effect on three
evolutionary processes
linked to the decrease of
diversity in the gene pool
and the rapid increase in
frequency of favourable
alleles in the gene pool.
frequency in the gene
pool more rapidly with
inbreeding.

diversity of the small
population that has
already occurred in
bottleneck effect /
founder effect /
genetic drift as the
breeding of closely
related individuals
increases the
chances of the loss
of alleles from the
gene pool.
Favourable alleles
selected for in NS will
increase in frequency
more rapidly with
inbreeding.

Closely related
individuals have
alleles in common.
A mutation that
creates a new allele
will be more
common in related
individuals.
Inbreeding will
therefore increase
the chances of a
mutation spreading
through the
population and so
becoming
established /
increasing in
frequency in small
gene pool.

Favourable alleles
are selected for so
increases in
frequency in the
gene pool.
Inbreeding will
increase the spread
of these favourable
alleles through the
small gene pool so
further increasing
their frequency.
Judgement Statement
Achievement
Two questions answered
correctly.
Minimum of 2 x A.
Achievement with Merit
Achievement with
Excellence
All questions answered
correctly including TWO at
Merit level.
All questions answered
correctly including TWO at
Excellence level.
Minimum 2 x M + 1 x A
Minimum 2 x E + 1 x A