Genetics Biology Worksheet ANSWERS

QUESTION ONE: DNA AND VARIATION
Genes determine many of the features of organisms, such as the
colour of the flowers on a plant.
A gene is a part of a DNA molecule.
The type of plant shown in the photograph below can have red or
white flowers.
ANSWER ONE: DNA AND VARIATION
For Achievement your answer should have TWO correct statements. E.g.
describes either a gene (a section of DNA that codes for a particular feature /
protein) OR an allele (an alternative form of the gene for the same feature)
a gene codes for a protein which then determines a feature
a different base sequence (alleles) results in differing plant features such as red
or white flowers
For Merit your answer should have TWO correct explanations. E.g.
explains the difference between a gene and an allele in terms of how they
impact on features
explains that the base sequence on a gene determines the appearance of a
particular feature
shows the relationship between DNA, a gene and an allele in a diagram (below)
Red flowers are due to a dominant allele and white flowers are due
to a recessive allele.
Discuss how information in DNA gives organisms (like the plant
above) their individual features, such as red and white flowers. In
your answer, you should:
explain the difference between a gene and an allele
draw a labelled diagram to show the relationship between a gene
and an allele and the structure of a DNA molecule
explain how the base sequence on DNA determines a particular
feature (eg, flower colour) and different forms (variations) of that
feature (eg, red and white flowers)
For Excellence your answer needs to link the explanation of the structural
relationship between DNA, genes and alleles with the explanation of the
production of a particular feature and variation within that feature.
Explanation of determination of feature and variation:
Along the DNA, base sequences provide the code for building different proteins,
which then determine particular features. Specific sections of the DNA determine
individual features such as flower colour. Variations in the feature (eg red or
white flowers) are due to (slight) differences in the sequence of the bases making
up a gene. The different variations of a particular gene are called alleles and they
cause the variations in the phenotypes. (The above diagram must also be shown)

QUESTION TWO: SEXUAL REPRODUCTION
Meiosis is a particular form of cell division that produces male and
female gametes.
(a)
Describe what gametes are and explain why they are needed
for sexual reproduction.
ANSWER TWO: SEXUAL REPRODUCTION
(a) For Achievement you need TWO statements describing gametes. E.g.
A gamete is a sex cell (e.g. an egg or sperm),
A gamete has half the normal number of chromosomes as body cells.
For Merit you need a correct explanation of the need for gametes:
It is required in sexual reproduction to ensure that when a sperm fuses with an
egg, the resulting first cell of the new organism has the correct number of
chromosomes.
Meiosis contributes to genetic variation.
(b)
Discuss how meiosis contributes to genetic variation, and why
genetic variation is important in a population. In your answer,
you should:
describe what is meant by genetic variation
explain how the process of meiosis leads to genetic
variation
explain why genetic variation is of benefit to a population
You could draw labelled diagrams to support your answer.
(b) For Achievement you need TWO statements describing genetic
variation. E.g.
Description of genetic variation:
Genetic variation refers to a variety of different genotypes for a particular trait
within a population.
That the separation of alleles/ chromosomes during meiosis results in new
combinations of alleles
That variation aids survival when conditions change.
For Merit you need a correct explanation of the need for gametes: E.g.
meiosis produces genetic variation in a population by the separation of alleles
which then allows new combinations of alleles to occur at fertilisation (this could
include a labelled diagram of the meiosis process
variations in a population might allow individuals to survive in changing
conditions (and to pass on the ability to their offspring)
For Excellence your answer needs to link the explanation of why genetic
variation within a population is important for the survival of the species
with the explanation of how inherited variation is constantly being
generated by the process of meiosis, through the reshuffling of alleles. E.g.
Meiosis produces gametes with half the number of chromosomes. This means
that pairs of alleles are separated at meiosis.
At fertilisation, which sperm fertilise which egg is due to chance and this results
in new combinations of alleles. These new combinations of alleles cause
variation
The advantage of variation to a species is that it may enable some individuals
to survive if some threatening event occurs. For example, if a new disease
arrives, not all individuals will be wiped out.

QUESTION THREE: MONOHYBRID CROSSES
The allele for a cleft chin (D) is dominant over the allele for a
smooth chin (d).
ANSWER THREE: MONOHYBRID CROSSES
For Achievement you need THREE statements (from of a), b), and c) E.g.
In (a) describes what a dominant allele OR relevant punnet square linked to
pedigree diagram
in (b), gives a reason for the presence of one of the alleles of the genotype
in (c), completes the Punnett Square correctly
D
d
D DD Dd
The pedigree diagram below shows the chin types in a family.
d Dd dd
in (c), gives the correct probabilities for cleft chin and smooth chin.
Probability of cleft chin = ¾ or 75% or 3 out of 4
Probability of smooth chin = ¼ or 25% or 1 out of four
(a)
(b)
Explain how evidence in the pedigree diagram shows that the
cleft chin allele (D) is dominant over the smooth chin allele (d).
In your answer, you should:
Describe what the term dominant allele means
draw a Punnett square(s) to show your reasoning.
Explain why the genotype of male A in generation 2 of the
pedigree diagram must have the genotype Dd.
For Merit you need TWO explanations
in (a), explains the evidence that shows that cleft chin allele is dominant. E.g.
A and B who both have a cleft chin produce a smooth chin child. If the cleft chin
allele was recessive (d) they would not be able to produce a child with a
smooth allele (as they would both have to be dd and would have no D allele to
pass on), so the cleft chin allele must be dominant OR other correct evidence
from chart.
In (b), explains why individual A must have a dominant and a recessive allele
using evidence from the pedigree diagram. E.g. As male A has a cleft chin this
must mean that he carries at least one cleft chin allele (D). Male A and female
B have a smooth chin boy, which means that A must have passed on a smooth
chin allele (d) to the boy as to be smooth chinned the boy must have two
recessive alleles, one from each parent.
In (c), gives the correct probabilities based on the completed Punnet square
parent alleles AND indicates that these can’t be used to predict what an
individual will be. E.g.
Probability of cleft chin = ¾ or 75% or 3 out of 4
Probability of smooth chin = ¼ or 25% or 1 out of four
However these are only probabilities and cannot be used to
predict the genotype of individuals

(c)
Individuals A and B, as shown on the pedigree diagram,
decide to have another child. They draw a Punnett square to
find what type of chin their child might have.
Explain why the result predicted by the Punnett square may
not accurately tell them what type of chin their child will have.
In your answer, you should:
draw a Punnett square to show the cross between
individual A and individual B
determine the probabilities of the child having a cleft chin
and having a smooth chin
explain why the ratio of children born into the family with
cleft and smooth chins may not match the probabilities.
For Excellence you need to have at least ONE Merit explanation from a) and
b) and for c) your answer needs to link the theoretical probabilities derived
from the correctly completed Punnett Square for with the explanation of
why the actual outcomes for families will not necessarily match the
predicted outcomes, especially when dealing with small population
samples.
Explanation of discrepancy:
Random fertilisation of eggs by sperm means that number of offspring showing
a particular variation will not always match the probability predicted by a
Punnett square, unless the number of offspring is quite large. Each child is a
unique and random genetic event.

QUESTION FOUR: SURVIVAL
Mutations can occur in DNA during cell division.
Explain whether a mutation could be inherited if it occurred in a skin
cell of an individual. In your answer, you should:
describe what a mutation is
explain what determines whether a mutation is able to be
inherited or not.
ANSWER FOUR: SURVIVAL
For Achievement you need ONE statement E.g.
Correctly defines or describes a mutation: A mutation is a change to the base
sequence of a gene along the DNA of an organism or a change in the genetic
code.
States that a skin cell mutation is not inheritable (or similar)
For Merit you need ONE explanation E.g.
If the mutation occurs in a gamete (or a cell that undergoes meiosis), then it
would be inherited. As a skin cell is not a gamete, a mutation in a skin cell
cannot be inherited.
QUESTION FIVE: GENETICS
Explain how two parents who don’t show a particular characteristic
can have a child who does show that feature.
In your answer include:
The nature of the characteristic
What causes a feature to be expressed (shown)
What is different (genetically) between the parents and the child
ANSWER FIVE: GENETICS
For Achievement your answer should talk about 2 – 3 points from:
The characteristic must be recessive
For a recessive feature to show a person must have two alleles for that feature
For a dominant feature to be shown (or a recessive feature to be hidden) the
person must have at least one allele for that feature
The parents must be heterozygous
The child is homozygous recessive for that feature
The parents must have at least one allele each for the (recessive) characteristic
in order to pass it on to the child
The child must have both alleles for the (recessive) feature for it to be shown
For Merit a reasonable explanation covering all the bullet points must be
given
The feature is linked to a recessive allele. Recessive alleles are only expressed if
a dominant allele is not present. Both parents would have to be heterozygous for
that characteristic. This means that they would have the dominant allele and the
recessive one and only show the characteristic represented by the dominant
allele. The child inherits one allele from each parent and if they inherit the two
recessive alleles then they will exhibit the recessive characteristic.

QUESTION SIX: VARIATION
A population of plants, species A, living in a certain area shows a
lot of variation in its leaf size, from very small to very large as
shown in the graph below.
Leaf size of plants of species A
ANSWER SIX: VARIATION
For Achievement you need ONE statement E.g.
For Merit you need ONE explanation E.g.
explains what causes variation (e.g. The variation in plants of species A may be
due to differences (mutations) in the sequence of bases in a particular gene)
Explains how variation aids the survival of the species. E.g.
Plants of species A have different sized leaves, and when the environment
becomes more shaded some plants will be better adapted to the new
conditions and therefore will survive).
Explanation of effect of reduced light:
Those individuals of plant species A whose leaves are large will be better
adapted to live under lower light levels. They will survive better and produce
more offspring, increasing the number of larger leaves plants in the
population.
Explanation of fate of poorly adapted plants:
Plants with average or small leaves will not be able to absorb enough
sunlight and make sufficient food. In time these plants might die off.
Leaf size affects the ability of a plant to absorb sunlight and make
food. Plants with larger leaves can live in areas with lower light
levels.
A new plant, species B, starts growing in the same area as
species A. Species B plants grow taller than species A plants,
which reduces the light available to plants growing below species
B.
Discuss how variation in leaf size occurs in the starting population
of species A and explain how this might help species A to survive
when species B starts growing in the same area.
In your answer, you should consider:
what causes variation within a population
the effect of reduced light on different individuals of plant
species A
For Excellence your answer needs to link the explanation of how genetic
variation arises within a plant species with the explanation of how that
genetic variation aids survival of the species in a changing environment
(eg, when environmental conditions are changed to lower light levels, the
larger leaves of some plants of species A, means that they are better
adapted to survive and reproduce, thus ensuring the survival of some
individuals, and hence the species).
Explanation of causes of variation: The variation in plants of species A may be
due to differences (mutations) in the sequence of bases in a particular gene.
AND
Explanation of effect of reduced light:
Those individuals of plant species A whose leaves are large will be better
adapted to live under lower light levels. They will survive better and produce
more offspring, increasing the number of larger leaves plants in the population.
OR
Explanation of fate of poorly adapted plants:
Plants with average or small leaves will not be able to absorb enough sunlight
and make sufficient food. In time these plants might die off.

QUESTION SEVEN: GENETICS
Cloning involves making an exact copy of an organism. Selective
breeding involves the breeding together of organisms that possesses
highly desirable characteristics.
Compare and contrast selective breeding and cloning.
Your answer should include
How the offspring compare to their parents
Their relative advantages and disadvantages
ANSWER SEVEN: GENETICS
For Achievement your answer should talk about 3 – 4 points from:
Cloned offspring have the same DNA as the parent (No variation)
Selective breeding means that the offspring have differences to their parents
(variation)
Advantages of selective breeding: All offspring are slightly different so there is an
increased chance that some will survive changes in the environment / diseases
It more likely that wanted characteristics will be passed on
Selective breeding can enhance a particular characteristic (I.e. make cows
bigger)
Disadvantages of selective breeding: There is no guarantee that the desired
features will be passed on (random process);
If the breeding group is too small inbreeding may occur with undesirable
characteristics being passed on
Advantages of cloning: Unlike selective breeding, which is a random process,
with cloning you know exactly what you will get
There is a 100% chance that any desired feature will be passed on
Disadvantages of cloning:
As there is no variation (change) you cannot improve on the original
As there is no variation a disease that will affect one will affect all
The cloned organism may develop “old age conditions” earlier than they should
For Merit you need to give a definition of what cloning and selective
breeding are and at least 2 advantages or disadvantages explained in detail
Selective breeding involves the breeding together of organisms that possess
highly desirable characteristics. This increases the chances of the desired
characteristics being passed onto the offspring. It is a random process and the
outcome / offspring are not guaranteed to possess the desired characteristic.
Therefore a number of the offspring will not have the desired characteristic.
Offspring will have a range of characteristics, inherited from both parents (I.e.
there is genetic variation) and will be different in multiple ways (Possibly superior
or inferior).
Cloning is also about getting desired characteristics in offspring. However,
cloning produces offspring that carry the DNA of only one parent, making
offspring genetically identical to that parent. This means there is a 100% chance
that the offspring will have the desired features. (No variation) This means that
there is no chance the offspring will be superior or inferior to the parent in some
way.
In summary while both methods are about increasing the chances of offspring
having desired characteristics; selective breeding gives variation but no certainty,
while cloning gives certainty but no variation.
For Excellence as for Merit but 3 advantages / disadvantages explained

QUESTION EIGHT: GENETICS
There are many genes used by pedigree cat breeders to get a range of
colours, fur length and body shapes. Several genes can control coat
colour in cats.
One of these produces the Agouti pattern, where each hair has a black tip
but bands of light and dark towards the hair root. This causes a cat to
have a striped appearance. This pattern is dominant, and denoted by the
letter A. The recessive allele for this trait gives plain black hairs.
(a)
A breeder wishes to have a pure breeding group with the Agouti
coat colour. He has a group of the Oriental breed pictured above,
some of which are black and some of which are Agouti.
Discuss how he would go about developing a pure breeding
Agouti group. Include punnet square(s) in your answer.
In the future it may be possible for breeders to simply sell copies of a
cloned Agouti cat rather than rely on selective breeding. Cloning involves
taking a cell from the parent and making an identical copy of the parent.
The genetic characteristics of the animals obtained by these two breeding
techniques will be different.
(b) Discuss the reasons for the differences in the genetic characteristics
of the cats produced by selective breeding and cloning. In your
answer you should:
Consider the type of cell division
involved in each breeding technique.
Variation (or lack of it) in the offspring
ANSWERS EIGHT: GENETICS
(a) For Achievement your answer should have ONE correct statement.
Eg:
He needs to do a test/back cross to find AA cats to breed together / AA are pure
breeding for agouti (a)
Breed agouti with black to find out which are AA
AND punnet/s (a)
For Merit your answer should explain process of test / back cross (m)Eg:
He needs to do a test/back cross to find AA cats to breed together/AA are pure
breeding for agouti. This means breeding the agouti with the black, if any black
kittens result, the agouti parent must be Aa and not pure breeding (m)
OR
appropriately annotated punnets ie
Punnet 1 – all agouti
A A
a Aa Aa
a Aa Aa
Punnet 2 – ½ agouti. ½ black
A a
a Aa aa
a Aa aa
For Excellence your answer should discuss the process of test cross to
establish pure breeding group (e) Eg:
The breeder first needs to find the AA agouti cats to breed from. By breeding the
agouti cats he has with the black ones, he can see this as AA x aa will only
produce Aa agouti kittens as in punnet 1. Quite a large number are needed to
ensure no black kittens will result. If a single black kitten is born, the agouti
parent must be Aa as in punnet 2, it must have given an a allele. When the
breeder is certain he has AA individuals he can breed only these, as all offspring
will be AA true breeding agouti, as no recessive alleles are present.
AND
Correct Punnett squares.
(b) For Achievement you need to describe a difference between cloning
and selective breeding or describe the processes of cloning and
selective breeding. (a) Eg
Cloning is a mitotic division but selective breeding is meiosis. OR
Cloning means there is no variation in the offspring whereas in selective breeding
there is variation in offspring. OR
Only one parent contributes all the genes/ genetic material / chromosomes in
cloning but two parents do in selective breeding.

For Merit you should give a reason for the difference in the genetic
characteristics based on the type of cell division in EITHER selective
breeding OR cloning. (m) Eg
Cloning means there is no variation in the offspring because they are produced
by mitosis
Or
In selective breeding there is variation in offspring. This is due to meiosis.
For Excellence you should give a reason for the difference in the genetic
characteristics based on the type of cell division in BOTH selective
breeding AND cloning. Eg
Cloning means there is no variation in the offspring whereas in breeding there is
variation in offspring. This is due to meiosis being used in normal breeding. In
meiosis, the homologous pairs line up and genetic material is exchanged
(causing variation) They are pulled apart, ie the alleles are separated. Each
gamete receives one allele for each gene, ie 1/2 the genetic material of the
parent. This combines randomly at fertilization with another gamete to give the
various different outcomes.
Cloning would lack variation as it uses mitosis. In mitosis the chromosomes line
up along the equator of the cell and an exact copy of each chromosome is made.
The chromosomes are then pulled apart and the cell splits in two leaving two
identical chromosomes (no variation)