Download 2010 exams4u feedback to students

Level 2 Bio Genetics 2010
Feedback to students
OVERALL
• Very poor attempt by many students.
• LOTS OF REVISION NEEDED!
• Often you must answer all parts of a question
correctly to gain the achieved grade for that
question.
OVERALL
• Q1 generally completed well but without
getting an achieved or higher in a question
relating to gene pool you will not pass the
external exam. You MUST show knowledge
across all areas of the standard to pass (i.e.
mendelian genetics AND population genetics)
YOU MUST LEARN DEFINITIONS!!!
• Writing just the names of the terms should be
done only when the question states IDENTIFY
or NAME.
• DESCRIBE or DEFINE: means basically “give the
definition for the key terms”.
• N.B. If in doubt give the definition of the key
words in the question. This is often all that is
required for the Achieved grade.
DEFINITIONS YOU MUST KNOW
The following terms were often misused or
incorrectly
defined
student exam
answers:
N.B.
There are
more in
definitions
that you
should
topic.
• Allele know for this •genetics
Gene pool
However
ones that were
in the
• Gene these are just the
• Evolutionary
process
particular set of• questions
used
• Organism
Genetic Drift
in
this
school
exam.
• Species
• Natural Selection
• Population
• Test cross
• Community
• Inbreeding
QUESTION ONE
Question
ONE
Achievement
4A or better
Merit
Excellence
2M and 2A 1E, 2M
or better
and 2A or
better
N.B. Each question was made up of
parts. Each part was assigned a
grade and these grades were then
totalled for your overall grade for
each question.
QUESTION ONE a)
Achievement
Merit
Excellence
Duroc : bbww
Hampshire : BBWW
F1 : BbWw
• Most answered correctly
• Required genotype of parents
– NOT their gametes
therefore
needed 2 B/b alleles AND 2 W/w
alleles
QUESTION ONE b)
Achievement
Pure breeding means that the
individual has a homozygous
geneotype / can produce only one
type of allele
Merit
Excellence
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.
• Again learn your definitions!
• Many on the right track but what
was written was not correct.
• N.B. pure breeding is a term used to
describe an individual – it is not the
mating process!
QUESTION ONE c)
Achievement
Gametes correct
Merit
Excellence
Whole Punnet Square correct
• Most did this well
• If you did not get an M then you
must get some help to get this right
in the future.
• There will definitely be a dihybrid
cross to complete in the external.
QUESTION ONE d)
Achievement
One of bbWW; bbWw
Merit
Both bbWW and bbWw and no other
genotype given.
• Many repeated bbWw
Excellence
QUESTION ONE e)
Achievement
Merit
3/16 or 3 : 15
or correct decimal (0.1875) or
18.75%
• Most did this correctly
Excellence
QUESTION ONE f)
Achievement
Merit
Excellence
Gives genotype as
bbWW and describes
breeding suspect pigs
with recessive
genotype (bbww) pigs
i.e. test cross
AND check whether
offspring have white
bands or are solid red
only.
OR Good attempt at
Punnet Squares with
probabilities and linked
in answer
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 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.
• Many failed to identify that a TEST
CROSS was required
QUESTION ONE f) cont
• Red is recessive therefore only appears
when there is no B allele present.
Punnet squares can therefore be
simplified to monohybrid crosses of
W/w alleles.
• Many did not read the information
provided to recognise the desired
pure breeding phenotype for this
question was red with a white band.
QUESTION ONE f) cont
• Many failed to mention that lots of
crosses would be needed to make
“almost certain” that the unknown
individual was bbWW
• Many did not say that if only one
offspring of the test cross had
recessive “no band” phenotype then
the unknown parent was
heterozygous so should be kulled as
not pure breeding.
QUESTION TWO
Question
TWO
Achievement
2A or better
Merit
Excellence
1M for (c) 1E, 1M
and 1A or and 1A
better
QUESTION TWO a)
Achievement
Merit
Excellence
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 gametes.
OR both correctly identified and
1½ reasonable descriptions
• DESCRIBE does NOT mean “only name”
• A Mutation does NOT make a new
GENE – it makes a new allele
• Source = where it comes from
QUESTION TWO b)
Achievement
Mutation with brief description of
how it shows in individual or in
gene pool
OR
Migration with correct description
(as question states gene pool – not
species)
Merit
Excellence
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.
• Question was flawed as a) was
regarding a species and b) was
regarding a gene pool hence alteration
in italics above.
QUESTION TWO c)
Achievement
Describes Natural selection as
causing :
•mutations that are helpful /
favourable to become established
in the gene pool / produce more
offspring
OR
•mutations that are helpful /
unfavourable to not become
established in the gene pool
OR
•Correct definitions of NS and
links to gene pool e.g. increase in
allele frequency of favourable
alleles (or vise versa for
unfavourable alleles)
Merit
Explains ONE of ;
•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
Excellence
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
• NS acts on PHENOTYPE (NOT
genotype/allele/gene). This leads to
increase/decrease of the ALLELES for
that phenotype in the next generation
QUESTION TWO c) cont
• Most answers lacked link to gene
pool
• NS is NOT mate selection
• NS still occurs even in a stable (i.e.
non-changing) environment
QUESTION THREE
Question
THREE
Achievement
2A or 1M
or better
Merit
Excellence
1M and
1E, and 1A
1A or better
QUESTION THREE a)
Achievement
Merit
Excellence
Any three with correct (or
reasonable attempts at)
descriptions for each of :
Bottleneck effect
Founder effect
Genetic drift
Mutation
Natural selection
• Majority of students did not know
what an evolutionary process was.
• Many did not read the question so did
not give three processes or only named
them and did not give a description.
QUESTION THREE a) cont
Descriptions for this example include:
• Bottleneck effect – eg numbers of
robins were greatly reduced so likely
loss / reduction in allele frequency
with likely a reduction in genetic
diversity.
QUESTION THREE a) cont
• 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 genetic diversity.
QUESTION THREE a) cont
• 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.
• Mutation – changes to genetic code
creating new alleles. If occurring in
gamete producing cells will enter
gene pool as inherited.
QUESTION THREE a) cont
• 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.
QUESTION THREE b)
Achievement
Merit
Excellence
Describes 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
•Mutations that are favourable
will become established / increase
in frequency in the gene pool
more rapidly with inbreeding.
•Favourable alleles selected for in
NS will increase in frequency
more rapidly with inbreeding.
Or gives a comprehensive
explanation of inbreeding (as per
merit column)
Explains inbreeding eg
•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
•Inbreeding will reduce the genetic 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.
•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.
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.
QUESTION THREE b) cont
• Definition of inbreeding often too
basic or poorly worded. Many did
not recognise that the main problem
with inbreeding is that it increases
the chances of (harmful) recessive
alleles coming together in offspring
and being expressed thus reducing
the fitness of the individual.
• Others, because of lack of recall on
evolutionary processes, failed to
achieve second part of question.
QUESTION ONE
• Lorem ipsum dolor sit amet,
consectetuer adipiscing elit.
Vivamus et magna. Fusce sed sem
sed magna suscipit egestas.
• Lorem ipsum dolor sit amet,
consectetuer adipiscing elit.
Vivamus et magna. Fusce sed sem
sed magna suscipit egestas.
JUDGEMENT STATEMENT
Achievement
Achievement with
Merit
Two questions
answered correctly.
Minimum of 2 x A.
All questions
answered correctly
including TWO at
Merit level.
Minimum 2 x M + 1
xA
Achievement with
Excellence
All questions
answered correctly
including TWO at
Excellence level.
Minimum 2 x E + 1
xA
REMEMBER:
• READ THE INFORMATION PROVIDED
• READ THE QUESTION – underline the key
terms
• ATTEMPT ALL PARTS OF ALL QUESTIONS! If
you are not sure then simply put the
definitions of the key terms.
QUESTION ONE
Achievement
Two questions answered
correctly.
Minimum of 2 x A.
Achievement with Merit
All questions answered
correctly including TWO at
Merit level.
Minimum 2 x M + 1 x A
Achievement with
Excellence
All questions answered
correctly including TWO at
Excellence level.
Minimum 2 x E + 1 x A