100 Science Genetics

Year 11 100
Science
Genetics
Ms Gibellini

Achievement Standard
Biological concepts and processes relating to variation in phenotypes
as adaptive features will be selected from:
 inheritable and non-inheritable variations that exist within a group of
living organisms
 differing rates of survival by various members of a group may
depend on their phenotype
 the importance of variation within populations (population and
species survival) in a changing environment such as pest infestation,
disease, drought, or flood
 the advantages and disadvantages of sexual reproduction.
The student must be familiar with the following genetic language and
conventions: gene, allele, mutation, genotype, phenotype, gamete,
zygote, dominant, recessive, homozygous, heterozygous, pure
breeding, Punnett square, and pedigree chart.
Contexts may be drawn from animals or plants. Links between DNA and
variation of phenotypes may require simple understanding of DNA structure
(bases).

Introduction to Genetics
What is genetics about?
Why is it important? How might it affect
you in the future?
 Complete page 89 of Scipad

SLO
• Explain the relationship between cells, nuclei,
chromosomes and DNA
• Describe the relationship between DNA, alleles,
genes and chromosomes.

Alleles, genes and
chromosomes
Alleles:
– alternative form of a gene
eg blue eyes (b) or brown eyes (B)
- sequence of bases (A, T, G, C) that makes
the different between blue and brown eyes
Gene:
– section of DNA that codes for a
characteristic
eg eye colour
Chromosome:
– coiled length of DNA (deoxyribose nucleic
acid)
- Made up of base pairs A, T, G, C

SLOs
 Draw a labelled diagram of a DNA molecule
using the terms nucleotide, triplet, sugar,
phosphate and base.
 Outline the role DNA plays in carrying
instructions to the next generation and
determining phenotype
 Explain that DNA contains the code for
making proteins, and proteins are the building
blocks for most of your body

DNA
 Deoxy ribose nucleic acid
 Double strand
 Double helix shape
 Bases – A joins with T and G joins with C
 (At The G.C)

Function of DNA
 DNA (base sequence (A,T,G,C) tell the cells what to
do, how to function and what type of cell to become
 DNA has the instructions of how to make proteins,
proteins are the building blocks of organisms and
make up enzymes
 DNA is structure simple and easily replicated over
and over using base pairing
 Double helix can coil into tiny chromosomes that fit
into the nucleus and carry a huge amount of
information

Success Criteria
1. Complete Scipad pages 90 - 96
2. 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).
 Explain the difference between a gene and an
allele.
 Discuss the difference between a chromosome,
gene and allele
 Discuss the structure and importance of DNA

 Explain the difference between a gene and an allele.
A gene is a section of DNA that codes for a characteristic (eye
colour), an allele is the alternative forms of that characteristic or
trait can take (blue or brown eyes)
 Discuss the difference between a chromosome, gene and allele
Chromosomes are coiled up lengths of DNA, sections of DNA make
up a gene and code for a characteristic, that characteristic (trait)
can come in different forms, these forms are called alleles
 Discuss the structure and importance of DNA
DNA (deoxyribose nucleic acid) is a double helix, it has a repeating
unit that consists of a phosphate group, carbon sugar and
nucleotide bases. The bases pair up A-T and G-C. DNA controls
the functioning of the cell, carries instructions for making proteins
and enzymes and determines which type of cell will form.
The importance of this structure is that DNA can be copied, it is
simple and can carry a huge range of information, coiled up to
become small enough to fit into nucelus

SLO
 Use the ‘base paring rule’ to help explain
the process of DNA replication

DNA Replication
 Every cell MUST have a complete copy of
DNA,
so before new cells can be made all the
DNA must be replicated (copied)

DNA Replication
Step 1: DNA unzips
Step 2: Free nucleotides match up A-T, G-C
(complementary base pairing) on both sides of
exposed DNA strands
Step 3: Two new daughter strands are formed,
containing one old and one new strand

Semi Conservative
When DNA replicates and makes two new
daughter strands, both new strands contain
one side of the original parent strand.

Success Criteria
1. Complete Scipad pages 97
2. Describe the roles of DNA in both carrying
instructions to next generation and determining
phenotype
3. 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).
4. Complete Scipad pages 98-103

SLO:
Key words: gametes, sex cells, egg, sperm, zygote,
asexual, sexual, reproduction, variation,

SLO
 Define variation in terms of being
continuous or discontinuous

25/09/2014
Variation
Variation is a name given to differences in a species,
e.g. dogs:
Variation is due to each animal having different GENETIC
INFORMATION in their cells.

Variation
 There are two types of variation
 Continuous – range eg height
 Discontinuous – either or, you have it or you
don’t, eg tongue roller

Discontinuous Variation
Characteristic Yes No
A B
Male Female
Widows peak Straight edge
Free ear lobe Attached ear
lobe
Straight
thumb
Hitch hikers
thumb
Tongue roller Non tongue
roller

Continuous Variation
 Complete Scipad pages 104-107
What shape is your graph?
 If your graph does not show a bell shaped
curve why not?
What is the biological importance of
variation?

SLO
 Discuss the advantages and
disadvantages of asexual reproduction in
terms of producing offspring that are
genetically identical (clones)

Reproduction
 Reproduction is the purpose of life!
Two methods of reproduction:
1. Sexual Reproduction
2. Asexual Reproduction

Chromosome Number
 Meiosis helps keep the chromosome number
constant, generation after generation.

Chromosome Numbers
 Chromosome numbers must be halved
during meiosis so that when an egg and
sperm join they only have 46
chromosomes (not 92, then 184, then 368!)
 If a problem occurs and there is an
uneven number of chromosomes then
division cannot occur and the individual is
usually sterile (cannot create offspring)
 Complete pages 154-155, 113 of
Workbook

Asexual Reproduction
 Involves one parent, that produces both
gametes which form a zygote
 Large numbers of off spring
 Identical offspring (clones)
 No variation – susceptible to changes in
environment
 Complete Scipad page 109

Why have sex?
What are the advantages of asexual
reproduction?
 Safer (less chance of predation during intercourse)
 Uses less energy (so energy can be used for growth
and repair)
 Faster
 Makes identical copies of organism that is currently
surviving well
 So why do most organisms carry out sexual NOT
asexual reproduction?

SLO
 Outline the process of mitosis and
understand the importance of making
daughter cells that do not show variation

Mitosis
 In order for an
organism to grow and
repair itself it needs to
make new cells
 Mitosis is cell division
which makes new cells
 Each new cell must
have a complete set
(46) of DNA in order for
the cell to function
properly (made via
DNA replication)

Mitosis
Step 1: First the DNA replicates, so that each cell has
an identical copy of DNA
Step 2:The Chromosomes line up at the equator
Step 3: Chromosomes are pulled apart by spindles to
opposite poles of the cell
Step 4: The cell membrane pinches in (cytokinesis) and
two new identical cells are formed (46 chromosomes
or 2n, diploid)

Success Criteria
 Explain why any body cell from an individual can
be used to establish their DNA profile.
Because every body cell has a complete set of DNA,
when new cells are made via Mitosis, DNA is
replicated creating two identical cells with complete
copies of DNA. Every cell requires a complete set in
order for the new cell to know how to function and to
be able to make more new cells

SLO
 Discuss the advantages and
disadvantages of sexual reproduction
 Describe the process of meiosis and
explain why it is important in generating
gametes.

Sexual Reproduction
 Requires male and female gametes from
separate parents
 Small numbers of offspring
 Large variation
 Complete Sci pad page 112

Sex gives rise to
Variation!!!!
Variation increases
chances of
Survival!!!!

Meiosis
 Meiosis is cell division which creates sex cells
(egg and sperm)
 Meiosis only occurs in testes and ovaries
 The new cells have half (haploid) the number
of chromosomes
 Involves two cell divisions, creating four cells
 The new cells are different from the parent cell

Success Criteria
 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.

SLO:
• Explain how sexual reproduction
produces new combinations of alleles
Key words: crossing over, recombination, recombinants,
homologous pairs

Crossing Over
 Crossing over occurs during meiosis when
chromosomes are lined up
 Crossing over creates new combinations of genes
(blue eyes and brown hair rather than blue eyes
blonde hair)
 New combinations, creates variation

Success Criteria
Meiosis contributes to genetic variation.
2. 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 may draw labelled diagrams to support your
answer.

Success Criteria
 Make a
poster/animation
showing Meiosis and
Mitosis, include
crossing over in
Mitosis

SLO
 Explain the importance of mutations in
forming new alleles

Mutations
 Mutations are a permanent change in the base
sequence of DNA
 Mutations are the ultimate source of variation as
they give rise to NEW phenotypes

Mutagens
 Mutations (changes in base sequence of DNA
are caused by:
 UV A rays
 Radio waves
 Some chemicals
 Heavy metals
 Problems during meiosis or DNA replication

Passing on Mutations
 Mutations can occur in the body cells or
the sex cells
 Mutations in the body cells only affect
that individual (skin cancer)
 Mutations in the sex cells are passed onto
the next generations (breast cancer)

Establishing mutations…
 Mutations can lead to phenotypes that
give an individual an advantage in
survival and therefore is selected for
mating and passes on the mutation to the
next generation
 Eg disease resistant, stronger muscles
 Mutations can also be disadvantageous
and lead to the organism being less fit
and therefore not reproducing and
passing on

Success Criteria
1. 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
2. Complete Scipad 114-115

SLO
 Discuss that individuals in a population
may have differing probabilities' of survival
based on their phenotype
 Explain the importance of variation within
a population in a changing environment
such as pest infestation, disease, drought,
or flood

Natural Selection
=
Survival of the fittest
=
EVOLUTION!

Natural Selection
Step 1: Variation; A variety of genes causes variation
in characteristics
Step 2: Differential Success; Some variations are
better at surviving
Step 3: Differential Fitness; The best survivors make the
best and most offspring
Step 4: Gene Pool Changes; Varieties that make
more offspring pass on more genes
Step 5: Evolution; Over time the population changes
towards one variety (the fittest)

25/09/2014
Evolution
My key observations:
1) All living things produce more
offspring than survive to adulthood
2) In spite of this, population sizes
remain roughly constant
3) Variation exists among species
4) Characteristics can be passed on
from one generation to the next.
These observations led me to the
conclusion that species evolve
over a along period of time by a
mechanism called “Natural
Selection”. The main evidence for
this is from fossil records.

25/09/2014
Natural Selection
1) Each species shows variation:
2) There is competition within each
species for food, living space,
water, mates etc
4) These survivors will pass on their
better genes to their offspring who
will also show this beneficial variation.
Get off
my land
Gutted!
Yum
3) The “better adapted” members of
these species are more likely to
survive – “Survival of the Fittest”

Genetic Variation
Variation within your genes can arise during:
 Fertilization
Sexual recombination (egg and sperm joining)
 Meiosis:
 Independent assortment (Mixing of mother and fathers
genes – random alignment of homologous pairs during
metaphase)
 Crossing over
Mutations

Independent Assortment
 Mixing of mother and
fathers genes
 Random alignment of
homologous pairs
during metaphase
(independent
assortment)
 Creates new
combinations

Types of Variation
 New combinations
 Meiosis – Independent assortment (mixing of
mothers and fathers genes)
 Crossing over
 Totally new trait (characteristic)
 Mutations
 Ultimate source of variation

Success Criteria
Genetic variation is important in a
population.
(a) Describe what is meant by the term
genetic variation
(b) How does genetic variation arise
(c) Explain its importance to a population.

Selective Breeding
 Video

Selective Breeding
 Over many generations farmers select
organism with desirable traits and mate
them
 Along the way the organisms without the
desirable trait are discarded
 Eventually all the population carry the
desirable trait

Nature or Nurture
 Is variation caused by differences in
genes or the environment?
 Types of variation:
 Physical – what an organism looks like
 White fur or brown fur
 Physiological – how an organism works on the
inside
 Rate of metabolism
 Psychological – how an organism thinks
 intelligence

Nature or Nurture?
Genetic Environmental Both
Hair colour(if dyed), eye colour, intelligence, height, weight,
blood group, scars, skin colour, number of fingers, metabolism,
religion, language, nose shape, tongue rolling, strength

Success Criteria
 Complete Scipad pages 105, 116-125
 List all the different words that mean
nature and nurture
 Describe what is meant by the term
genetic variation, and explain its
importance to a population.

Success Criteria
 Nature
 Born with it
 Inherited
 Innate
 Genetic
 Nurture
 Get it over time
 Acquired
 Environment
 Learned
 Not inherited

Success Criteria
A teacher developed deafness last year as
a result of having noisy classes.
 Discuss the likelihood of this type of
deafness being inherited by the 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

SLO:
Key words: dominant, recessive, homozygous,
heterozygous, genotype, phenotype, gametes

SLO
 Distinguish between the terms genotype
and phenotype
 Distinguish between the terms
heterozygous and homozygous
 Distinguish between the terms dominant
and recessive

Terms;Terms;Terms;Terms
Term Definition
Phenotype Physical characteristic, blue eyes
Genotype Letters representing alleles, Bb
Homozygous Same letters (alleles) BB, bb
Heterozygous Different letters (alleles) Bb
Alleles Alternative form of a gene
Dominant Always expressed if present, capital letter, B
Recessive Requires two alleles to be present to be
expressed, lower case letter, b
Pure breeding Homozygous for the desired trait

Success Criteria
 Complete Scipad page 126, 128, 143, 144

SLO
Describe how gender is determined

Boy or Girl
Parent Phenotype: Male X Female
Parent Genotype: XY x XX
Gametes: X Y x X X
Punnet Square: X X X
X XX XX
Y XY XY
F1 Genotype: 1 XY : 1 XX
F1 Phenotype: 1 Male : 1 Female

Boy or Girl
 Sex is determined by the male,
 if a sperm carrying a Y chromosome fertilizes an egg the
baby is a _______________
 if a sperm carrying an X chromosome fertilizes an egg
the baby is a _______________
 There is a 50% chance of a baby being a boy or
girl, no matter how many boys in a row are born
there will always be a 50% chance the next one
will also be a boy

Success Criteria
 A couple are expecting their third child. They already
have one boy and one girl.
(a) 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

SLO
 Carry out genetic crosses using Punnett
Squares.
 Determine genotypic and phenotypic
ratios

Predicting Offspring
Parent Phenotype: Brown x Brown
Parent Genotype: Bb x Bb
Gametes: B b x B b
Punnet Square: X B b
B BB Bb
b Bb bb
F1 Genotype: 1 BB : 2 Bb : 1 bb
F1 Phenotype: 3 Brown : 1 Blue

Punnet Square Rules
 Heterozygous x Heterozygous cross
= 3 dominant phenotype: 1 recessive phenotype
 Homozygous dominant cross
= All dominant phenotype
 Heterozygous X recessive cross
= 1 dominant phenotype: 1 recessive phenotype
 Recessive X recessive cross
= All recessive phenotype

Success Criteria
 Complete worksheets
 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).
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.

1) In mice, white fur is dominant. What type of
offspring would you expect from a cross between a
heterozygous individual and one with grey fur?
Explain your answer with a genetic diagram.
2) A homozygous long-tailed cat is crossed with a
homozygous short-tailed cat and produces a litter of
9 long-tailed kittens.
Show the probable offspring which would be
produced if two of these kittens were mated and
describe the characteristics of the offspring (hint:
work out the kitten’s genotype first).

SLO:
• Use pedigree charts to determine
genotype and phenotype
Key words: dominant, recessive, homozygous,
heterozygous, genotype, phenotype, gametes

Pedigree Questions
I
II
III
1. What is the genotype of individual I2? Justify your answer
2. What is the genotype of individual III3? Justify your answer
3. What is the genotype of individual III4.?Justify your answer.
4. What is the genotype of individual III 1? Justify your answer
5. Complete Scipad page 138-141

Test Cross
 Test crosses are used to
determine whether an
organism is homozygous or
heterozygous dominant
 Cross the unknown organism
with a recessive organism
 If the offspring show the
recessive trait then the parent
must have been
heterozygous,
 both parents must supply a
recessive trait in order for
offspring to be recessive

Success Criteria
 Complete Worksheets

Revision
 Complete worksheets
 Complete all activities on the workbook cd
 Complete revision summary notes
 Create a mind map of this topic
 Complete practice test, on moodle, and mark it

Achievement Standard
Biological ideas relating to genetic variation are limited to concepts and processes
connected with:
 the continuity of life based on the inheritable nature of DNA
 links between DNA and variation in phenotypes
 variation in phenotypes as adaptive features.
Biological concepts and processes relating to the inheritable nature of DNA will be selected
from:
 the roles of DNA in both carrying instructions to the next generation and determining
phenotype
 the relationship between DNA, alleles, genes, and chromosomes
 the way in which genotype determines phenotype
 the way chromosomes exist as pairs so that individuals inherit two copies of each gene.
Biological concepts and processes relating to variation in phenotype will be selected from:
 the significance of an allele as an alternative version of a gene
 the role of mutations in forming new alleles
 the role of meiosis in generating gametes (students are not required to provide the
names of the stages of meiosis)
 the significance of sexual reproduction (in producing a new mix of alleles)
 the patterns of inheritance involving simple monohybrid inheritance showing complete
dominance, sex determination, possible genotypes, and phenotype ratios.

100 Science Genetics

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