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BIOLOGY
BIOLOGY
BIOLOGICAL IDEAS RELATING TO
GENETIC VARIATION
4 CREDITS(90948)
THE SKILLS YOU NEED TO KNOW:
DNA, GENES,
CHROMOSOMES
p 55
MITOSIS
p 59
MEIOSIS
p 61
•
•
•
•
DNA is the genetic code in the nucleus of cells
A Chromosome is a strand of coiled up DNA
DNA consists of sequences of bases: A, C, T & G
A Gene is a section of DNA that codes for a
particular trait (hair colour, eye colour etc.)
• A cell copies itself and splits in half, creating two
identical daughter cells
• Occurs in the body cells (all except sex and blood
cells). It is used for growth and repair
• Meiosis only occurs in the sex cells
• Gamete – male and female sex cells; the sperm
and eggs
• Zygote – The resulting one-celled organism, after
a female egg is fertilized from a male sperm
• There are two stages of cell division resulting
in four cells (gametes) that each have half the
number of chromosomes
• The male and female gametes combine to give a
zygote with the full number of chromosomes
• Pure Breeding – When parents on both sides are
homozygous dominant or homozygous recessive
PUNNET SQUARES
p 68
• Punnet squares show the possible genotypes of
offspring, based on the genotypes of the parents
• Phenotype ratio - compares the number of
offspring with different physical traits
• Genotype ratio - compares the number of
offspring with different alleles
PEDIGREE DIAGRAMS
ALLELES
p 57
GENETIC
VARIATION
p 64
• An allele is the expression of a gene
(e.g. either blue or brown allele for the
eye colour gene)
• The dominant allele is the one that is
always expressed (if it’s present)
• The recessive allele will only be
expressed if there are NO dominant
alleles present
• Genotype is the genetic code an
organism has for a particular trait (e.g.
TT, Tt, tt)
• The phenotype is the physical
appearance of that genotype (e.g.
brown eyes, blue eyes etc.)
• Homozygous is when two alleles are
the same (e.g. TT or tt)
• Heterozygous is when two alleles are
different (e.g. Tt)
• Allows a population to survive by
adapting to a changing environment.
Variation can come from:
• Meiosis – where four different cells are
produced
• Crossing over – where genes are
swapped between chromosomes
• Mutations – these are changes in DNA
sequence and can occur before or after
birth. Mutations can result from any
number of factors
p 73
• Punnett square (genotype/phenotype) information can be
shown on family trees
• This outlines ‘affected’ people (usually homozygous recessive)
Note: Problems may
rely on knowledge
from earlier biology
sections
PAGE 53
Exam Tip:
Answering Questions
A basic rule that’s often broken:
DON’T WASTE TIME ON DIFFICULT QUESTIONS.
By answering one question that you struggle with, you might be
missing out on five questions that you can do.
If it’s hard, move on and come back to it later if you have time.
PAGE 54
BIOLOGY
DNA, GENES,
CHROMOSOMES
SUMMARY
•
•
•
•
DNA is the genetic code in the nucleus of our cells.
A Chromosome is a strand of DNA that has been coiled up
DNA is made up of a sequence of bases; A, C, T and G
A Gene is a section of DNA that codes for a particular trait (hair
colour, eye colour etc.)
• An allele is the expression of a gene (e.g. either blue or brown
allele for the eye colour gene)
For a complete tutorial on this topic visit www.learncoach.co.nz
OLD NCEA QUESTIONS
1. 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.
PRACTICE QUESTIONS
2. What is a function of chromosomes?
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 shown) 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 (e.g. flower
colour) and different forms (variations) of that
feature (e.g. red and white flowers)
3. Genes, chromosomes and DNA are important in
inheritance. Describe is the relationship between
genes, chromosomes and DNA.
PAGE 55
ANSWERS
NCEA
PRACTICE
1. A gene is a section of DNA that codes for a particular
2. One of the following is required:
feature (protein) while an allele is the forms the gene
takes.
•
•
Chromosomes carry genetic information or DNA
Chromosomes control characteristics or traits
of organisms.
• Chromosomes control activities of cells.
• Chromosomes are code for proteins.
(Achieved)
3. A gene is a small part of a chromosome. A
chromosome is made up of a long, coiled strand
of DNA. Part of this DNA sequence, and therefore
part of the chromosome, codes for a particular
characteristic (e.g. eye colour). This section is called
a gene.
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 (e.g. red or white flowers)
are due to (slight) differences in the sequence of the
bases making up the gene. The different variations of
a particular gene are called alleles and they cause the
variations in the phenotypes.
(Excellence)
(Merit)
Study Tip:
Last Minute Study
If you are running out of time:
• Focus on topics that came up often in class
• Don’t bother studying topics that haven’t been covered in
class. They probably won’t be in the exam
• The LearnCoach summaries are a good place to start!
PAGE 56
BIOLOGY
ALLELES
SUMMARY
• An allele is the expression of a gene (e.g. either blue or brown allele for the eye colour gene)
• The dominant allele is the one that is always expressed (if it’s present). The recessive allele
will only be expressed if there are NO dominant alleles present
• Genotype is the genetic code an organism has for a particular trait (e.g. TT, Tt, tt)
• The phenotype is the physical appearance of that genotype (e.g. brown eyes, blue eyes etc.)
• Homozygous is when two alleles are the same (e.g. TT or tt)
• Heterozygous is when two alleles are different (e.g. Tt)
For a complete tutorial on this topic visit www.learncoach.co.nz
OLD NCEA QUESTIONS
1. One trait in squash plants is the colour of the fruit.
White fruit are due to a dominant allele (F) and
yellow fruit are due to a recessive allele (f).
a. Explain the difference between a gene and an
allele.
b. The alleles for the colour of squash fruit
combine to produce THREE different genotypes,
but only TWO phenotypes.
PRACTICE QUESTIONS
2. Describe the difference between the terms allele
and gene.
3. Kevin was interested in breeding mice. Genes control
the fur colour of these mice. They can have grey or
white fur. Grey mice are homozygous recessive for
this fur colour gene.
a. Discuss the relationships between chromosomes,
genes and alleles.
b. Show the symbols for grey and white fur that
could be used in a punnet square.
4. Yellow coated mice result from an allele N that is
present in the mice genotype. The n represents the
normal allele. The genotype NN is lethal so there
are no live homozygous yellow coated mice. Jane
crossed two mice with yellow coats and counted the
live offspring. These are her results:
Coat Phenotype
Number of Offspring
Yellow
40
White
20
a. What fraction of the mice have yellow coats?
b. What is the genotype of a white coated mouse?
5. Define the term homozygous.
Explain how the alleles combine to produce only
two different squash colours – white and yellow.
In your answer you should:
• Define genotype and phenotype
• State the three different genotypes
produced and the phenotype of each
6. When harvesting wheat it is easier if the plants have
short stems. Tall stems (T) are dominant over short
stems (s). What is the genotype of a plant with a
short stem?
7. Define the term heterozygous.
8. A certain breed of dog can have either a long tail or
no tail at all. The allele for the long tail is recessive
and is given the symbol t.
a. What is the phenotype of a dog with the alleles
tt?
b. What is the genotype of a dog which is
heterozygous for no tail?
9. A variety of flower produces either purple or blue
flowers. A botanist wants more blue flowers. The
allele for blue flowers is dominant over the allele for
purple flowers.
a. Define the word dominant as it is used in
genetics.
b. Give the genotype for a purple flower if the blue
flower is given the letter W.
10. In breeds of dog, there is a gene that produces an
extra toe or “dewclaw”. This is a dominant trait. State
the genotype of a dog that has the normal number of
toes and explain why this genotype results in normal
toes. In your answer you should use the terms allele
and recessive.
PAGE 57
ANSWERS
NCEA
1.
3.
specific sections of DNA, which carry instructions
for the characteristics of an organism. Alleles
are different expressions of the same gene. For
example, the gene for fur colour in mice has two
alleles: one for grey fur and one for white fur.
(Merit)
b. Grey fur = f
White fur = F
(Achieved)
a. A gene is a selection of DNA that codes for a
characteristic or trait such as hair or eye colour,
an allele is a different form of a gene, with a
different combination of bases; A, T, G and C.
Each gene has more than one allele and the
dominant one(s) will always be expressed if they
are present, for example brown or blue eyes.
(Excellence)
b. Genotypes Ff and FF give the phenotype of
white squash fruit.
Genotype ff gives the phenotype of yellow
squash fruit.
The genotype describes which alleles are
present and the phenotype is the expression of
these alleles, i.e. What a trait looks like. In this
case the fruit with the dominant allele (F) will be
white, and the fruit with both recessive alleles (f)
will be yellow.
When the dominant allele (F) is inherited the fruit
will always be white. This means homozygous
dominant will be white.
When one of each allele is inherited,
(heterozygous genotype Ff or fF) the dominant
allele will be observed in the phenotype.
It isn’t until both recessive alleles (ff) are present
that the yellow phenotype will be observed.
Hence, only two (white, yellow) phenotypes will
result from three different genotypes.
(Excellence)
PRACTICE
2. Genes encode specific instructions for the
characteristics of an organism. Alleles are a different
expression of the same gene and therefore express
different physical characteristics (phenotypes).
(Achieved) one definition correct.
(Merit) two definitions correct.
PAGE 58
a. Chromosomes are lengths of DNA. Genes are
4. a. 40/60=2/3 (Achieved)
b. Genotype = nn
(Achieved)
5. Homozygous means having two identical alleles for a
gene.(Achieved)
6. Genotype = ss
(Achieved)
7. Heterozygous refers to a situation when two genes
that an organism possesses for a trait are different, e.g.
Ff(which represents a dominant and a recessive gene).
(Achieved)
8.
9.
a. No tail(Achieved)
b. Genotype = Tt or tT
(Achieved)
a. A dominant allele produces the same phenotype
whether it is with a homozygous or heterozygous
allele. If the dominant allele is present, it is fully
expressed phenotype (even in a heterozygote).
(Achieved)
b. Genotype = ww.
(Achieved)
10. The genotype of a normal dog is tt. This results in
a normal number of toes because the dog has only
inherited the recessive alleles (t). There is no dominant
allele (T) present to inhibit the recessive allele, so
the trait of the extra toe cannot occur in the dog.
(Excellence)
BIOLOGY
MITOSIS
SUMMARY
• A cell copies itself and splits
in half, creating two identical daughter cells.
• Occurs in the body cells (all
except sex and blood cells).
It is used for growth and
repair.
For a complete tutorial on this topic visit www.learncoach.co.nz
PRACTICE QUESTIONS
1. The diagrams below show how a cell reproduces.
2. Mitosis is a type of cell division.
purpose of mitosis.
Describe the
3. After an embryo has been formed, either by cloning
or by sexual reproduction, it grows by cell division.
What is the name of this type of cell division?
a. The order is incorrect. Please place them in the
b.
c.
correct order. The first letter has been given to
you.
(1) ..D..
(2) .......
(3) .......
(4) .......
(5) .......
Name the objects labelled X, shown in image E.
In which part of a cow does this type of cell
division occur?.
Study Tip:
Evaluation
After Each Exam ask yourself:
• Where did most of the questions come from?
• Which parts ate up most of my time?
• Was I anxious during the exam? If so why?
• What could I do differently next time?
PAGE 59
ANSWERS
PRACTICE
1.
a. (1)D
(2)A
(3)E
(4)B
(5)C
(Merit)
b. Chromosomes or chromatids
(Achieved)
c. This type of cell division occurs everywhere in
the cow except for the ovaries or testes and
blood.(Achieved)
2. The purpose of mitosis is to produce identical
daughter cells. These cells are used for growth and
repair in the body.
(Achieved)
3. Mitosis(Achieved)
Study Tip:
Motivation
When you study well for an exam:
• Treat yourself for giving it your best shot
• Watch a movie with friends or get some takeaways
Small rewards motivate you to try your best in whatever you do.
PAGE 60
BIOLOGY
MEIOSIS
(SEXUAL REPODUCTION)
SUMMARY
• Meiosis only occurs in the sex cells
• There are two stages of cell division resulting in four cells (called gametes) that each have half
the number of chromosomes
• The male and female gametes with half the number of chromosomes combine to give a zygote
(fertilized egg) with the full number of chromosomes
• Gamete – male and female sex cells; the sperm and eggs
• Zygote – The resulting one-celled organism, after a female egg is fertilized from a male sperm
• Pure Breeding – When parents on both sides are homozygous dominant or homozygous
recessive
For a complete tutorial on this topic visit www.learncoach.co.nz
OLD NCEA QUESTIONS
1. Meiosis is a particular form of cell division that produces male and female gametes.
Describe what gametes are and explain why they are needed for sexual reproduction.
PRACTICE QUESTIONS
2. There are 94 chromosomes in the body cell of a
8. A kangaroo has 16 chromosomes in each of its cells.
3. The normal chromosome number for toucans is 106.
a. How many chromosomes would there be in a
9. A wolf has 39 chromosomes in each egg cell. How
goldfish. How many are found in the gamete?
b.
sperm cell of a male toucan?
What is the name of the process that produces
gametes?
How many chromosomes will there be in its gamete?
many chromosomes will this wolf have in each of its
skin cells?
10. A scientist wanted to produce a hybrid crayfish
by mating a fast growing crayfish with a different
crayfish that had good flavour. He injected the
sperm from a crayfish that had 202 chromosomes
in each body cell into the egg of a crayfish
which had 96 chromosomes in each egg cell.
How many chromosomes would there be in
a fertilized egg resulting from this technique?
Show your working to explain your answer.
4. Philip has two pedigree great Danes that he is
breeding. A dog has 78 chromosomes.
a. How many chromosomes are in each sperm cell
and also in each cell of an embryo?
b. What does the term pedigree mean as it is used
above?
5. Fur colour in mice is determined by the allele B
(grey fur) and the allele b (white fur). Barry is a
pedigree white mouse. He escapes and breeds
with a wild grey mouse. Barry’s white fur b is
recessive to the grey fur B of the wild mouse.
Some of Barry’s offspring were then collected.
Explain whether the white offspring will ever show
their wild ancestry through coat colour.
6. There
are 23 pairs of chromosomes in
each human body cell. One of these pairs
of chromosomes is the sex chromosomes.
Discuss why sex cells have 23 chromosomes,
whereas body cells have 46. Refer to the cell division
processes involved.
7. A mule, which is created when a horse and a donkey
mate has 63 chromosomes. Explain why the mule
would not be able to produce sex cells.
11. Why do cells produced by meiosis have fewer
chromosomes than their parent cells
12.
a. Name process A on the diagram above.
b. Name the cell labelled B, which forms as a result
of process A.
c. What type of cell division occurs when cell B
forms an embryo?
d. Explain what happens to the number of
chromosomes in each cell during cell division for
growth.
PAGE 61
ANSWERS
7. The mule will not be able to produce sex cells
NCEA
because it has an odd number of chromosomes.
Meiosis cannot occur in this case.
(Merit)
1. A gamete is a sex cell (e.g. an egg or sperm) which
has half the normal number of chromosomes as body
cells. 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.
(Merit)
8. 8 chromosomes(Achieved)
9. 78 chromosomes(Achieved)
10. The number of sperm will have half the number of
body cells (202 / 2 = 101). The 101 chromosomes
from the sperm + 96 chromosomes from the egg
gives a total of 197 chromosomes.
(Merit)
PRACTICE
2. Half of 94 = 47. Therefore, there are 47 chromosomes
3.
in the gamete.
(Achieved)
a. 5 3 chromosomes.
b. Meiosis.
(Achieved)
(Achieved)
4. a. 39 chromosomes.
(Achieved)
b. It means that the parents are known and are
homozygous.
(Achieved)
5. It won’t because for the mouse to be white it needs
to be homozygous recessive and so there is no grey
gene left to bring out.
(Merit)
6. Gametes have only 23 chromosomes so that when
the male and female sex cells combine their 23
chromosomes, there is a full set of 46 chromosomes
in the zygote. The 23 chromosomes are produced
via meiosis. The parent cell is divided twice giving
four resulting cells each with half the number of
chromosomes. However, mitosis is used in the body
for growth and repair, therefore, both the parent and
daughter cells must contain the full 46 chromosomes
to function.
(Excellence)
11. Gametes have fewer chromosomes because in
meiosis a cell undergoes two cell divisions, producing
four cells each with half the number of chromosomes
as the parent cell. This allows male sex cells to
be combined with female sex cells and produce
offspring with the correct number of chromosomes.
(Merit)
12.
a. F ertilisation/conception
(Achieved)
b. Cell B is a zygote or fertilised egg
(Achieved)
c. Mitosis(Achieved)
d. During growth mitosis occurs. Therefore, the
total number of chromosomes remains the
same.(Achieved)
Study Tip:
Pre-Exam
Before an Important Exam:
Don’t: spend a lot of time talking with classmates who haven’t
studied.
Do: Avoid negative vibes and focus on your own preparation
and goals.
PAGE 62
BIOLOGY
Study Tip:
Study Enhancement
If you are spending long hours studying or
working remember to:
• Drink fluids
• Eat well
• Sleep well
• Do regular exercise and move around occasionally while
studying
It’s the basics that can make some of the biggest differences.
PAGE 63
GENETIC VARIATION
SUMMARY
• Genetic variation allows a population survive by adapting to a changing environment.
Variation can come from:
• Meiosis – where four different cells are produced, any of which could be passed on to
different offspring
• Crossing over – where genes are swapped between chromosomes (in the first stage of
meiosis)
• Mutations – these are changes in DNA sequence and can occur before or after birth.
Mutations can result from any number of factors (some examples include: radiation, random
errors in DNA replication, insertion, deletion, repeats, substitutions )
For a complete tutorial on this topic visit www.learncoach.co.nz
OLD NCEA QUESTIONS
1. Genetic variation is important in a population.
a. Describe what is meant by the term genetic
b.
variation, and explain its importance to a
population.
One process that produces genetic variation is
mutation. Explain what mutations are and how
they contribute to genetic variation. In your
answer you should include:
• What a mutation is
• The effect of mutations on genes, alleles and
DNA
• Whether all mutations are passed on to the
next generation
4. Mutations can occur in DNA during cell division.
a. Explain whether a mutation could be inherited if
b.
it occurred in a skin cell of an individual.
In your answer, you should:
• Describe a mutation
• Explain what determines whether a
mutation is able to be inherited or not
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.
2. One of the parents of a baby is a teacher who developed
deafness last year as a result of having noisy classes.
Discuss the likelihood of this type of deafness being
inherited by their new baby.
In your answer you should consider:
• The reason for the parent’s deafness
• What types of characteristics are inherited
• The effects of genetics and the environment on
deafness in offspring
3. Meiosis contributes to genetic variation. 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
PAGE 64
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
BIOLOGY
PRACTICE QUESTIONS
5. Maize has 20 chromosomes in each of its cells. Cells
can divide in one of two ways: mitosis or meiosis.
Study the information in the table below:
Mitosis
Meiosis
Number of daughter
cells produced
2
4
Chromosome
number in daughter
cells
20
10
Variation
Nill
Yes
Purpose
Growth
Reproduction
Discuss why meiosis is used for reproduction, rather
than mitosis. In your answer, consider:
• The processes of mitosis and meiosis
• How variation occurs in meiosis
• The chromosome number in daughter cells
6. Originally dogs looked very different to the modern
breeds we have today. How, with the help of humans,
have different breeds of dog originated from a single
ancestral dog type? Please discuss.
7. A common trait of fruit flies is curly wings. Even
though it is dominant they don’t occur often in
nature. Why is this?
9. A New Zealand kiwifruit marketer is developing a
red kiwifruit. The vines, which have a particular
genetic mutation, were bred for this trait.
A whole orchard with the red fruit trait can be
obtained by either selective breeding or by cloning/
taking cuttings. The genetic characteristics of the
plants obtained via these two methods will be
different.
Discuss the reasons for the differences in the genetic
characteristics of the plants produced by selective
breeding and cloning/cuttings. Consider the type of
cell division involved in each breeding technique.
10. In July 1996 the first successful cloning of an animal
occurred, Dolly the sheep. Discuss the genetic
advantages of producing a sheep by cloning, rather
than from sexual reproduction. In your answer you
should:
• Explain the cloning process, including the type
of cell division involved
• Explain the sexual reproduction process,
including the type of cell division involved
• Identify the differences in the offspring
produced by cloning and sexual reproduction
• Discuss the advantage of cloning compared to
sexual reproduction
8. Cloning is where plants or animals are copied exactly.
Cloning makes genetically identical plants or animals
to their parents. Normally only cuttings of plants, or
identical twins in animals, are identical.
a. Explain why cloning only involves mitosis while
sexual reproduction involves meiosis and
mitosis?
b. Plants and animals can be created through either
sexual reproduction or cloning. Please compare
the biological advantages and disadvantages of
these two different methods of reproduction.
Study Tip:
Cramming
Cramming helps some people.
But don’t lose sleep. Getting your normal sleep will ensure you
are your best physically and mentally for the exam.
PAGE 65
ANSWERS
NCEA
1. a. Genetic variation is important in populations
b.
to ensure the survival of a species when an
environment changes. Genetic variation refers
to the different DNA sequences of offspring,
caused through mutations, crossing over and
meiosis. These differences in DNA sequence
can cause individuals to have a different
phenotypes. This variation of phenotype means
that some individuals are better equipped for
survival than others. If these variations occurred
in the gametes (sex cells) then individuals that
are better equipped to survive would produce
offspring that also have higher survival rates than
others. In this way the population will slowly
produce offspring that is increasingly suited to
the new environment.
(Excellence)
A mutation is a change in genetic material / DNA
/ genes of an organism. When a mutation occurs,
the base sequence of the gene changes; this
results in completely new alleles. If mutations
occur in the gametes, these new alleles have
the possibility of being passed on to offspring.
If mutation occurs in body cells, only the one
individual will show variation – the change will
not be passed on. Mutations do not always result
in variation, but when they do, the variation is
often in the form of entirely new alleles.
(Excellence)
4. a. 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. If the mutation occurs in a
gamete, then it would be inherited. As a skin cell
is not a gamete, a mutation in a skin cell cannot
be inherited.
b. The variation in plants of species A may be due
to differences (mutations) in the sequence of
bases in a particular gene and due to the process
of meiosis.
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.
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.
(Merit - either a or b correct)
(Excellence - a and b correct)
PRACTICE
5. Meiosis is used for reproduction, whereas mitosis
noises related to teaching. Deafness was caused by
‘environment’, not genetics. (The question makes
no reference to him having inherited deafness, nor
was he born with it). Only genetic characteristics
can be inherited, not those acquired as a result of
environment. It is unlikely any of his children will
be born deaf, as it appears the deafness was caused
by environment, not genetics. However, we cannot
determine whether they will be deaf at any stage
in their life, as deafness can be work- related and it
depends on the job they have later in life.
(Excellence)
is used for growth and repair. This is because
meiosis causes variation in the offspring. Meiosis
halves the chromosome number so that when two
gametes come together at fertilisation a full number
of 20 are restored. Meiosis randomly causes one
chromosome from each of the 10 pairs to pass into
the daughter cell. As each member of a chromosome
pair carries different alleles, each daughter cell will
receive different combinations of alleles to pass on
to their offspring. This means that offspring will show
genetic variation from each other, and from their
parents. Mitosis cannot be used for reproduction,
as it produces two identical cells in the plants. The
identical nature of the daughter cells means that
mitosis cannot produce variation in offspring. Also,
because mitosis doesn’t halve the chromosome
number to 10, there would be double the number
when the two gametes met, producing maize with
40 chromosomes.
(Excellence)
3. Genetic variation refers to a variety of different
6. Different modern breeds of dog have all come from a
2. The parent / teacher became deaf because of loud
genotypes (different DNA sequences) within a
population. Meiosis produces gametes with half
the number of chromosomes. This means that pairs
of alleles are separated at meiosis. At fertilisation,
the sperm which fertilises the egg is purely due to
chance. This results in new combinations of alleles.
The advantage of variation to a species is that it may
enable some individuals to survive if a threatening
event occurs. For example, if a new disease arrives,
not all individuals will be wiped out, as some may
randomly be immune due to genetic variation.
(Excellence)
PAGE 66
single ancestral dog type through selective breeding.
Selective breeding means that breeders choose from
the natural variation present in the dogs. Different
breeds have come about through selecting for
certain desirable traits, such as hair colour, texture,
or nose lengths. Dogs that share desirable traits are
then mated together to produce similar offspring. If
the mating is carried out over generations, then all
undesirable traits can be bred out and a new dog
breed will result.
(Excellence)
BIOLOGY
7. If there are only a few curly winged flies, then curly
wings must not be a favourable trait for survival. If
curly winged flies cannot easily get food or escape
predators, then they will die quickly without a
chance to breed and pass on their dominant genes
to their offspring.
(Merit)
8.
a. With cloning, the entire parent cell is used for
the daughter cell and mitosis is then used for the
reproduction of that cell. Sexual reproduction
uses meiosis first to split up the chromosomes
and then recombine them in fertilization. Mitosis
can then be used for cell duplication once a
zygote has been formed. (Merit)
b. Cloning is an advantage if the parent has
favourable traits but is not good if the parent has
any genetic weaknesses. Cloning is preferable
when a parent has traits that are desirable.
A negative effect is that cloning reduces the
diversity of a population and hence its ability
to adapt to unexpected events such as climate
change or an epidemic. If sexual reproduction
is used, the traits of the offspring are unknown.
This is good as it allows a population to adapt to
changing environments.
(Excellence)
10. There are several advantages for a commercial
farmer to clone sheep. The major advantage of using
a cloned lamb is the selection of desirable traits each clone would have exactly the same traits as its
parent and these would be known. Desirable traits
might include fast wool growth and a good colour.
Similarly, undesirable traits can be avoided. Cloning
means that offspring are produced via mitosis, where
identical daughter cells are produced. This ensures
that the clone is genetically identical to the parent.
If the lamb was to be born through sexual reproduction,
it would inherit genetic material from both parents.
This would occur by meiosis, when the gametes (egg
and sperm) join to restore the chromosome number.
Once these have fused, the cell would replicate by
mitosis as it grows into an embryo. This would give
genetic variation in the offspring, rather than the
identical offspring produced through cloning. There
are some disadvantages to using cloning over sexual
reproduction. Over time genetic variation in the flock
decreases, which leaves the flock more vulnerable to
disease or other adverse events that could be avoided
with selective breeding. This is because selective
breeding produces variation, which could allow the
population to adapt to a changing environment. (Excellence)
9. Cloning/taking a cutting from a vine involves taking
cells from the existing plant and creating new plants
via mitosis. The plant will grow up having exactly the
same genotype as the existing vine. Cloned plants
are usually genetically identical to their parent,
getting their entire DNA from that parent.
Selective breeding involves pollinating the vine of
the red kiwifruit with pollen from another vine.
Meiosis will produce zygotes some of which will have
the allele for red kiwifruit. The offspring will inherit
a mixture of genes from both parent vines; getting
their DNA from two different sources means that the
offspring will have a unique set of genes. Vines that
show the red kiwifruit phenotype will be saved for
further breeding. By continually doing this eventually
the whole orchard can be built up all producing red
kiwifruit.(Excellence)
PAGE 67
PUNNETT SQUARES
SUMMARY
• A punnet square shows the possible
genotypes of offspring, based on the
genotypes of the parents
• Phenotype ratio compares the ratio of
offspring with different physical traits
e.g.In the example to the right the ratio is 3:1
3 expresses B (BB, Bb and Bb) and 1
expresses b (bb)
• Genotype ratio compares the ratio of
offspring with different alleles
e.g.In the example to the right the ratio is
1:2:1
1 expresses BB, 2 express Bb, and one expresses bb
For a complete tutorial on this topic visit www.learncoach.co.nz
OLD NCEA QUESTIONS
1. A couple are expecting their third child. They already
have one boy and one girl.
Discuss the likelihood of their third child being a girl.
In your answer you should:
• Explain how sex is determined in humans
• Complete a Punnett square showing sex
inheritance
• Explain the relevance of the couple already
having children
PRACTICE QUESTIONS
2. A variety of plant produces red or yellow flowers.
The allele for yellow flowers is dominant over the
allele for red flowers.
a. Draw a Punnett square showing a cross between
a pure-breeding, yellow flowered plant (Y) and a
pure-breeding, red flowered plant (y).
b. How could a plant with red flowers appear as
a seedling from plants that had only produced
seedlings with yellow flowers for several
generations? Use Punnett squares.
3. Pea colour is determined by a single gene. Yellow
peas (P) are dominant over green peas (p). A green
pea plant is crossed with a yellow pea plant. There
is a mix of both green and yellow pea plants as
offspring. Jeremy buys some yellow peas from the
local seed merchant. Explain what he could do to
determine whether the peas were homozygous or
heterozygous. You may use Punnett squares as part
of your answer.
PAGE 68
4. When harvesting wheat it is easier if the plants
have short stems. Tall stems (T) are dominant over
short stems (s). Complete a Punnett square using
heterozygous parents for this trait.
5. A certain breed of dog can have either a long tail or no
tail at all. The allele for the long tail is recessive, and
is given the symbol t. A male dog is heterozygous.
The dog is crossed with a female dog that has the
same genotype.
a. Complete a Punnett Square for the offspring of
the cross.
b. Give the phenotype ratio of the offspring of the
cross.
c. The cross resulted in eight puppies, two of which
had no tail. Explain why this differs from the ratio
in (b) above.
d. Discuss how you could determine whether a no
tailed dog was homozygous or heterozygous.
You may use Punnett squares to help answer the
question.
BIOLOGY
6. One of the genes in cats is responsible for tabby
markings. Cats without this marking are homozygous
recessive for this gene (tt). Two cats without
markings are mated.
a. Complete the diagram at the bottom of the page
to show the possible genotypes of the offspring.
b. A female offspring from the mating described
in part (a) is crossed with a tabby male. Some
of their kittens have tabby markings and some
don’t. Explain why 50% of the offspring produced
from this cross would be expected to have tabby
markings. A Punnett square could be included in
your answer.
8. Yellow coated mice result from an allele N that is
7. A guinea pig had a litter of six babies. The babies
were all females.
a. Complete a Punnett square to show the expected
sex of the babies.
b. If the guinea pig had another litter, what
percentage of the babies would you expect to be
male? Explain your answer.
present in the mice genotype. The n represents the
normal allele. The genotype NN is lethal and the fetus
does not develop so there are no live homozygous
yellow coated mice. Jane crossed two mice with
yellow coats and counted the offspring. These are
her results:
a.
Coat Phenotype
Number of offspring
Yellow
40
White
20
i. Complete a Punnett square for the cross of
the heterozygous parents.
ii. In the Punnett square, what fraction of the
mice carries at least one N allele?
b. Explain why the fraction of yellow coated mice in
Jane’s experiment is different from the fraction
in (a)(ii) above.
Study Tip:
Music
• Can enhance learning for some
• Be a distraction for others
Find what works for you!
PAGE 69
ANSWERS
3. Jeremy could perform a cross with homozygous
NCEA
recessive (green) peas. If only yellow peas result
then the yellow seeds are homozygous. If green also
occurs then the seeds are heterozygous, as shown in
the Punnett square below.
1. Women are XX, so when they create eggs with half
the number of chromosomes, both eggs will have an
X chromosome. A male is XY so when they create
sperm, half will have the X chromosome and half will
have the Y chromosome. When the gametes come
together (egg is fertilised), there is a 50% probability
they will have a baby girl. The sex of the baby is
determined by whether it is an X or a Y (sperm) that
fertilises the egg. If it is X it will be female; if it is Y
it will be male. The fact that they already have one
girl and one boy has no effect on what the next baby
will be. Fertilisation is random at each event, and
previous fertilisations have no effect.
green pea
yellow
pea
4.
p
p
P
Pp
Pp
p
pp
pp
(Merit)
T
T
t
TT
Tt
t
Tt
tt
(Achieved)
5. a.
T
t
T
TT
Tt
t
Tt
tt
(Achieved)
b. 3:1 - three have no tail (TT, Tt and Tt), and one
has a long tail (tt)
(Excellence)
PRACTICE
sample. 3:1 is the expected ratio, however, a
different result can occur due to chance.
(Achieved)
d. Cross a known homozygous recessive dog
(genotype tt) with the dog being tested. An
analysis of the offspring of the test cross will
confirm the genotype of the no tailed dog. The
no tailed dog will be heterozygous if any of its
offspring turn out to have long tails. This can be
seen in the Punnett squares below.
2. a.
b.
Y
Y
y
Yy
Yy
y
Yy
Yy
(Achieved)
This could occur if two heterozygous yellow
flowered plants were crossed.
Homozygous
TT x tt
T
The parents of the crossed plants would both
have yellow flowers, but they would not
necessarily produce any red flowering plants.
They could still pass on the recessive allele to the
next generation. E.g. A homozygous dominant
(YY) and a heterozygous dominant (Yy):
(Excellence)
PAGE 70
(Achieved)
c. Natural variation occurs and in such a small
6.
a.
Heterozygous
Tt x tt
T
t
t
Tt
t
Tt
(Merit)
tt
(Achieved)
BIOLOGY
b. The genotype of the female offspring (from a)
must be tt. As some of the kittens don’t have
tabby markings, the genotype of the male must
be Tt (if the male was TT the kittens would all
have tabby markings). The Punnett square
below shows why 50% of the kittens would be
expected to have tabby markings.
t
t
T
Tt
Tt
t
tt
tt
(Achieved)
7. a.
X
Y
X
XX
XY
X
XX
XY
8. a.
i.
N
n
N
NN
Nn
n
Nn
nn
ii. 3/4
b. The fraction of yellow coated mice in the
experiment is less than the Punnett square
because ¼ of the offspring are NN yellow coated
mice. These NN mice don’t survive and are not
counted in the statistics. Also, the expected ratio
is only a theoretical expectation. In reality results
may vary, particularly if the sample is small.
(Merit - b correct)
(Excellence - a and b correct)
b. We would expect 50% of the babies to be male
as can be seen in the Punnett square above.
It is irrelevant that it is her second litter when
determining outcomes as it doesn’t rely on
previous results. This shows a phenotype ratio
of 2:2, meaning that we can expect 50% males.
(Merit - b correct)
(Excellence - a and b correct)
Study Tip:
Study Groups
Can help with exchange of ideas and with
motivation.
More isn’t always merrier.
The larger the study group, the more likely you are to get
distracted.
Small study groups (up to 4) work better.
PAGE 71
Study Tip:
Understand NCEA
You are sitting NCEA so:
UNDERSTAND the marking system
• Each question is marked out of 8 so attempt all three
questions in each topic.
• You can get up to 4 marks with Achieved parts. Merit parts
give 5 - 6 marks and Excellence gives 7 - 8.
• If you are aiming for Excellence, do the Excellence parts of the
question first. This gives you the full 7 - 8 marks straight away
for each question. Easier parts of the question do not give you
any extra marks (but they are a safety net if you’ve made a
mistake)
PAGE 72
BIOLOGY
PEDIGREE DIAGRAMS
SUMMARY
• Punnett square (genotype/phenotype) information can be shown on a
family tree
• This outlines ‘affected’ people (usually homozygous recessive)
• Homozygous recessive parents (‘affected’) will always pass on their
genes, producing homozygous recessive or heterozygous (carrier)
children
For a complete tutorial on this topic visit www.learncoach.co.nz
OLD NCEA QUESTIONS
1. Gorillas show an inherited recessive condition called
2. The allele for a cleft chin (D) is dominant over the
a. Explain how the pedigree chart can be used to
a. Explain how evidence in the pedigree diagram
albinism. This results in white fur. The pedigree chart
below shows the inheritance of albinism in a family
of gorillas. Normal fur is the dominant allele (N),
while albino fur is recessive (n).
show that albinism is a recessive trait. In your
answer you should:
• Define the terms dominant and recessive
• State the genotypes of albino and normal
gorillas
• Complete a labelled Punnett square to
support your answer
• Explain how your Punnett square shows that
albinism is a recessive trait
Note: Refer to the pedigree chart above.
b. Explain whether the genotype of the 3 normal
fur offspring in Generation IV can be determined,
based on the evidence in the pedigree chart and
your Punnett square from part (a)
allele for a smooth chin (d).
The pedigree diagram below shows the chin types in
a family.
b.
c.
shows that the cleft chin allele (D) is dominant
over the smooth chin allele (d).
In your answer, you should:
• Explain 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 shown above must
have the genotype Dd.
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
PAGE 73
PRACTICE QUESTIONS
3. A variety of plant produces red or yellow flowers.
5. A pedigree chart for a particular trait of parrots is
a. Which characteristic, yellow or red, is the
Determine the genotype of the parrots labelled A
and B. Support your answer with:
• Reference to specific parrots from the pedigree
diagram
• Reasons for which allele is dominant and which
is recessive
• A Punnett square.
The allele for yellow flowers is dominant over the
allele for red flowers. The following is a pedigree
chart showing the inheritance of flower colour in
their descendants.
b.
c.
recessive characteristic? Give a reason for your
answer.
Give the probable genotype of flower 1 and
explain why.
Give the probable genotype of flower 2 and
explain why.
4. Dogs have been domesticated for thousands of years.
During this time some characteristics have become
popular and selected by dog breeders to form new
breeds. A certain breed of dog can have either a long
tail or no tail at all. The allele for no tail is dominant,
and is given the symbol T.
a. Two dogs were selected by a breeder to be
mated. The male had a long tail and the female
had no tail. They had four puppies between
them, all with similar tails. Complete the
pedigree chart below by showing the genotypes
of the male and the puppies.
shown below.
6. Jamie likes to breed goldfish. In one breeding cycle
she mated two goldfish and had three resulting fish:
two gold and one black. The gold colour allele G is
dominant over the black.
a. Complete the pedigree chart with the genotype
of each fish. One gold coloured offspring has
been completed for you.
b. Jamie wants to breed black goldfish from the
b. The breeder chose two dogs, both heterozygous
c.
no tails to breed. Predict what the puppies from
their mating would be, by making a Punnett
square.
What proportion (or percentage) would you
expect to have a long tail?
PAGE 74
c.
d.
same parents. Complete a Punnett square to
predict the genotypes and phenotypes of the
offspring.
What proportion (or percentage) of the offspring
are expected to be black?
Explain why the predicted results in part (c)
are different to the actual results of the mating
shown in (a).
BIOLOGY
7. The pedigree chart below shows the inheritance
of a disease. White boxes show the creatures that
don’t have the disease. Use the chart to answer the
following questions.
9. Hundreds of years ago before cloning was around
farmers used selective breeding to make their herds
better. In cows, the traits of milk volume, hide colour
and meat quality have all been bred for.
a. A farmer with a herd of brown cows observes
two black calves. The parents are both brown.
If B represents the gene or allele for brown coat
colour which is dominant, complete the pedigree
chart to show the genotypes of both parents and
their two black offspring.
a. Is the allele for this disease dominant or
recessive?
b. Explain your answer to (a) above.
c. What is the expected genotype of the male with
the asterisk.
8. Barry is a pedigree white mouse. He escapes and
breeds with a wild grey mouse. Fur colour is
determined by the alleles B and b. Barry’s white fur
b is recessive to the grey fur B. Give the genotypes of
individuals A and B.
b. The farmer next chooses two cows to breed that
c.
are both heterozygous for high milk production.
High volume (l) is recessive to low volume (L).
Predict the genotype of the calves from this
cross by completing a Punnett square.
What percentage of the calves from the cross in
(b) would be expected to have a low volume of
milk?
Exam Tip:
Proofreading
• Only takes a few minutes
• Finds the silly mistakes
• Gives you extra marks (especially if your teacher is supermeticulous)
SO many people miss out on Extra Marks by not proof-reading
PAGE 75
ANSWERS
NCEA
1. a. Dominant means the trait will be expressed,
even if only one allele is present in a pair
(heterozygous). Recessive means the trait will
be expressed only if two alleles are present
(homozygous). It will be masked in the presence
of one dominant allele (heterozygous). Albinism
is a recessive trait. This can be established using
Generation III and Generation IV. In Generation
III, two normal individuals have three normal
offspring and one albino offspring. The only way
this is possible is for Generation III to both be Nn.
When two n alleles come together, a homozygous
recessive nn (albino) offspring forms. If normal
was recessive, Gen III individuals would be nn.
There is no way of forming an individual with N
in its genotype.
b. As male A has a cleft chin this must mean that
c.
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, to be smooth chinned
the boy must have two recessive alleles, one
from each parent.
D
d
D
DD
Dd
d
Dd
dd
Probability of cleft chin = ¾ or 75% or 3 out of 4
Probability of smooth chin = ¼ or 25% or 1 out
of 4
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.
(Achieved - one of a, b or c)
(Merit - two of a, b or c)
(Excellence - all of a, b and c)
PRACTICE
3. a. Red flowers are recessive. This is because two
b.
(Excellence)
b. All three Normal fur offspring are either Nn or
c.
2. a. A dominant allele is the form of a gene that
4. a.
NN. Because their parents must have both been
Nn to produce albino offspring, there is a 25%
chance they are NN and a 50% chance they are
Nn. Their genotype cannot be established until
they produce offspring. (Excellence)
is always expressed whether the individual
has one or two copies of that allele.
A and B, who both have a cleft chin, produce
a smooth chin child. If the cleft chin allele was
recessive they would not be able to produce
a child with a smooth allele as can be seen in
the punnet square below, so the cleft chin allele
must be dominant.
PAGE 76
yellow flowers can have either yellow or red
offspring, while two red flowers have only red
flowers.
Yy (where Y is yellow and y is red) because there
are both yellow and red flowers in its offspring
so it must have one of each (heterozygous).
YY as even though it is reproducing with a
homozygous recessive plant it produces only
yellow flowers so it is likely to be homozygous
dominant.
(Achieved - one of a, b or c)
(Merit - two of a, b or c)
(Excellence - all of a, b and c)
b.
d
d
T
d
dd
dd
t
d
dd
dd
T
t
TT
Tt
Tt
tt
c. 25% would be expected to have a long tail.
(Achieved - one of a, b or c)
(Merit - two of a, b or c)
(Excellence - all of a, b and c)
BIOLOGY
5. A and B are heterozygous, or Pp. The trait is the
recessive characteristic. This is because the A
and B have offspring with the trait, even though
they themselves don’t have it. As the dominant
trait appears in them they must have at least one
dominant gene and because they produce offspring
with the (recessive) trait, they must also have a
recessive gene each. This is shown in the punnet
square below:
P
p
P
PP
Pp
p
Pp
pp
(Excellence)
6.
7. a. Dominant
b. Parents that are both recessive will result in
c.
a.
only recessive children, while parents with the
dominant trait can end up with any combination
of homozygous dominant, heterozygous and
homozygous recessive depending on the
genotype of the patents (DD or Dd). By looking
at the second generation, it can be seen that
two diseased mice mate and two without
disease mate. The parents without disease only
produce similar offspring, while the diseased
parents produce both diseased and without
disease offspring. This means that the diseased
is dominant.
Dd as it has both diseased and without disease
offspring.
(Achieved - one of a, b or c)
(Merit - two of a, b or c)
(Excellence - all of a, b and c)
8. A = bb (because he is white)
B = Bb (there must be B for the dominant grey fur
and a b from the white father).
(Achieved)
9. a.
b.
G
g
G
GG
Gg
g
Gg
gg
c. 25% of the offspring would be expected to be
black.
d. Each fish has a 25% chance of being black. This
probability doesn’t depend on what colour the
other siblings are as with sexual reproduction
egg and sperm fertilisation is random.
(Achieved - two of a, b, c or d)
(Merit - two of a, b, c or d)
(Excellence - all of a, b, c and d)
b.
L
l
L
LL
Ll
l
Ll
ll
c. 75% would be expected to have a low volume of
milk.
(Achieved - one of a, b or c)
(Merit - two of a, b or c)
(Excellence - all of a, b and c)
Study Tip:
Rewards
Reward yourself for passing a tough year!
Small achievements (e.g. topping a quiz) also deserve small
rewards
Maybe you could remind your parents about this one!
PAGE 77