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REVISION NOTES: SUMMARY OF B1 TOPIC 1:
Classification and genetics.
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Classification
1.1 Describe how biologists classify living organisms according to how closely they are
related to one another including:
a Species b Genus c Family d Order e Class f Phylum g The Five Kingdoms
As you go down
the levels the
organisms will
have more in
common and will
be more closely
related.
Animal cell and Plant cell
………………………………… cell
nucleus
…………………………… cell
Cell wall
Cell
membrane
Cytoplasm
Starch
grain
Chloroplast
Cytoplasm
Vacuole
nucleus
Plant cells have chloroplasts (containing chlorphyll) and animal cells
don’t.
Plant cells have a cell wall – animal cells don’t.
Cell Parts you need to know
Nucleus – controls the cell and contains DNA. (Same
for both plant and animal cells).
Cell wall – gives strength and support to plant cells.
Chloroplasts – contain chlorophyll which absorbs light
for photosynthesis so the plant cell can make glucose.
Kingdoms (See next slide)
1.2 Describe the main characteristics of the five kingdoms including
a Animalia
b Plantae
c Fungi
d Protoctista
e Prokaryotae
1.2 Describe the main characteristics of the five kingdoms including
a Animalia – are multi celled, have cells with a nucleus but no cell
wall or chlorophyll. They feed heterotrophically.
b Plantae - are multi celled, have cells with a nucleus, also have a
cell wall and chlorophyll. They feed autotrophically.
c Fungi - are multi celled, have cells with a nucleus and cell wall but
no chlorophyll. They feed saprophytically.
d Protoctista – single celled and have a nucleus.
e Prokaryotae – single celled and have no nucleus.
Kingdom:
Animalia
Kingdom:
Plantae
Kingdom:
Fungi
Kingdom:
Protoctista
Multi-celled
Multicelled
Multicelled
Single (uni) celled Single (uni) celled
Have nucleus
Have nucleus
Have nucleus
Have nucleus
No nucleus
Example:
euglena
Example:
bacteria
Have cell walls,
Have no cell wall , Have cell walls,
have chlorophyll do not have
no chlorophyll
chlorophyll,
Eat other
Use light from
the sun to make
organisms (feed
heterotrophically) own food (feed
autotrophically)
Examples:
Examples:
trees, flowers,
Fish, human
Absorb nutrients
from other
organisms or
dead and
decaying matter
(feed
saprophytically)
Example:
mushrooms,
Kingdom:
Prokaryotae
Euglena
Euglena
Euglena is difficult to classify as it has features of several kingdoms. It has
chloroplasts and so can feed autotrophically, which puts it in the plantae
kingdom. It has a gullet to take in food which puts it in Animalia. It can move
using a flagellum – putting it in the Animlia kingdom.
However, it is unicellular (single-celled) and has a nucleus. Therefore it is placed in
the Protoctista kingdom. It cannot be placed in prokaryotae as this kingdom has
no nucleus.
Grade
E: Canbe
youProkaryotae
recall the Grade
D:
Grade
Can you
discuss the
main
featuresdoes.
of all of
It cannot
as Prokaryotae
do
notC:have
a nucleus
and
Euglena
names of the kingdoms
and give examples of each.
Can you explain the
cell features of each
kingdom.
the kingdoms.
Grade B Extension: Classify euglena and justify your
decision.
Viruses
1.3 Explain why scientists do not classify viruses in any of the five kingdoms
and regard them as non-living.
The kingdoms consist of all the living organisms.
Viruses are not classified into any of the 5 kingdoms because
viruses are non-living and the kingdoms only contain living
organisms.
Viruses are classed as non-living because they do not fulfil all of
the 7 life processes. They can only reproduce.
They take over a host cell, injecting its DNA which makes the cell
make multiple copies of the virus. The viruses then explode
out of the cell, destroying it, and then go to destroy other
cells.
Vertebrates
1.5 Explain how scientists place vertebrates into groups
based on
a oxygen absorption methods – lungs, gills and skin
b reproduction – internal or external fertilisation,
oviparous or viviparous
c thermoregulation – homeotherms and poikilotherms
d body covering – fur / hair, feathers, dry scales, moist
skin, and wet scales.
Ready to learn starter:
Recall the 5 groups of vertebrates. Mammals, birds, reptiles, amphibians, fish.
What do all vertebrates have in common? They all have a backbone
(supporting rod running the length of the body)
What phylum do all vertebrates (including humans belong to?) Chordata (have
spinal cord)
Then give the characteristics of each vertebrate group.
Mammals use internal fertilisation and are viviparous. They are
homeothermic, have fur and obtain oxygen using lungs.
Birds use internal fertilisation and are oviparous. They are homeothermic, have
feathers and obtain oxygen using lungs.
Reptiles use internal fertilisation and are oviparous. They are poikilothermic,
have dry scales and obtain oxygen using lungs.
Amphibians use external fertilisation and are oviparous. They are
poikilothermic, have moist skin and obtain oxygen using gills, lungs and
through their skin.
Fish use external fertilisation and are oviparous. They are poikilothermic, have
wet scales and obtain oxygen using gills.
Thermoregulation
Body
covering
Oxygen
absorption
method
Internal fertilisation
Give birth to live
young (Viviparous)
and feed milk to them
Warm blooded
(Homeotherms)
Constant body
temperature
Have hair or fur
Have lungs to breathe
Internal fertilisation
Lay eggs (Oviparous)
Warm blooded
(Homeotherms)
Constant body
temperature
Have feathers
Have lungs to breathe
Have dry scales
Have lungs to breathe
Have moist, soft skin
Gills when young
Lungs when adults
Also absorb oxygen
through their skin
Have wet scales
Have gills to take in
oxygen from the water
Features
Reproduction
methods
Mammals
Birds
Reptiles
Amphibians
Fish
Internal fertilisation
Lay eggs
(Oviparous)
External Fertilisation
Lay eggs
(Oviparous)
External fertilisation
Lay eggs
(Oviparous)
Cold blooded
(Poikilotherms)
Body temperature varies
with the temperature of
its surroundings
Cold blooded
(Poikilotherms)
Body temperature varies
with the temperature of
its surroundings
Cold blooded
(Poikilotherms)
Body temperature varies
with the temperature of
its surroundings
One of the phyla of the Animalia
Kingdom is:
• The Chordata is the animal phylum that includes
humans and other vertebrates.
• (Note: not all chordates are vertebrates)
Kingdom: Animalia
Phylum: Chordata
1.3 Describe that all vertebrates have a spinal cord and therefore are
chordates.
1.4 Describe the main characteristics of the phylum chordata as animals
with a supporting rod running the length of the body, an example of this
being the backbone in vertebrates.
Chordate features
• Chordates have these features at some point in their life
• supporting rod (or backbone) - running the length of the body,
an example of this being the backbone in vertebrates.
• The job of the backbone is to protect the spinal cord.
Spinal cord - a bundle of nerves which runs down the "back".
Difficult keywords
oviparous
Lays eggs
viviparous
Gives birth to live young
homeotherms
Constant body temperature – animal can regulate
its own body temp
Body temperature varies with its surroundings –
animal cannot regulate its own body temp
poikilotherms
Internal fertilisation
Egg and sperm meet inside the female body – animals
have sex
External fertilisation
Egg and sperm meet outside the female body – usually
in water
ALL: Identify the 5 groups of vertebrates and give 1 feature for each group (Grade E)
MOST: Establish the main features of the 5 groups of vertebrates. Explain the words:
oviparous, viviparous, homeotherm, poikilotherm (Grade D)
SOME: Discuss how scientists classify vertebrates?
(Grade C)
1.6 Outline the problems with classifying vertebrates to a specific group
based on their characteristics and why many vertebrates are difficult to
classify.
Axolotl
• Difficult to classify because it has features of
fish and amphibians.
• It has gills as adults and spends all its time in
water. Poikilothermic (fish features).
• Has limbs and can walk, has smooth moist
skin, poikilothermic (amphibian features).
1.6 Outline the problems with classifying vertebrates to a specific group
based on their characteristics and why many vertebrates are difficult to
classify.
Platypus
• The platypus is the only mammal that lays eggs
which are leathery like reptile eggs. They also
have a skeleton like a reptile.
• They have fur and are homeotherms like
mammals .
• They have a beak and webbed feet like birds.
• Have features of more than one vertebrate
group.
Definition of hybrid
The animals in the pictures are all called
HYBRIDS
They are the offspring
from two different
species interbreeding.
They are neither species;
they show characteristics
of both parents.
Eg A lion and tiger
interbreed to have a
liger.
1.7 Discuss why the definition of a species as organisms that
produce fertile offspring may have limitations:
a some organisms do not always reproduce sexually (bacteria do
not interbreed they simply divide) and
b sometimes different species do interbreed to produce hybrids
and some are fertile (eg mallard ducks)
Definition of a species
“A species is a group of organisms that:
can interbreed (reproduce with one another)
and
produce offspring that are fertile (able to reproduce)
Three Limitations of a definition of a
species.
1. Occasionally different species do
interbreed to produce hybrids
2. Some organisms do not always reproduce
sexually (bacteria do not interbreed they
simply divide) and some plants make copies
of themselves.
3. Sometimes different species do interbreed
to produce hybrids and some are fertile (eg
mallard ducks)
Binomial classification
• 1.8 Know how to write a binomial name and what levels of classification each
name refers to.
Binomial names are the Genus and species of the
organism.
Genus
species
Homo sapien (wise human)
Capital
letter
Lower case letter
This is called the binomial system – all species are given a two part Latin name.
Rules:
First part of the name refers to the Genus
Always starts with a capital letter.
Second part of the name refers to the species
Always starts with a lower case letter.
Full name in italics.
•
•
•
•
ALL: Give 3 examples of hybrids. (Grade E)
MOST: Correctly identify and write binomial names. (Grade D)
SOME: Define the terms ‘species’ and ‘hybrid’ and suggest why these definitions may be limited. (Grade C)
FEW: Discuss why classification can be made complicated by hybrids (Grade B)
Polar bear correct binomial name
Ursus maritimus
First word genus starts with a capital letter,
Second species word is all lower case.
All in italics.
Binomial names
• If two different organisms have the same first
name (belong to the same Genus), it means
they are closely related.
• Panthera tigris
• Panthera leo
Both these organisms
belong to the same genus
and so are closely related
(common name = tiger)
(common name = lion)
Sample exam question:
Passer domesticus.
domesticus
The binomial name for a house sparrow is Passer
Draw two lines to correctly match the genus and species of the house
sparrow with its binomial name.
Passer
genus
sparrow
species
domesticus
Why is binomial classification useful?
• H 1.8 Explain why binomial classification is needed to identify, study
and conserve species, and can be used to target conservation efforts
The binomial classification is useful to when naming robins because America and England use
the same word (robin) for two different birds that are not the same species. See below.
The system is useful as it allows scientists to communicate clearly what species they are talking
about (avoids confusion).
Binomial classification is useful as it allows scientists to easily identify existing and new species.
They can also use it to see how closely organisms are related – if different organisms share the
same first name, they belong to the same genus and are closely related.
American Robin
Turdus migratorius
English Robin
Erithacus rubecula
HIGHER STUFF – Why is binomial classification useful?
They can also use the binomial system to identify areas in the world that have greater and lesser
biodiversity.
Biodiversity is the number of different species of organisms in a specific area. (Lots of different
organisms = great biodiversity / very few different organisms = lesser biodiversity).
You need to use binomial classification to identify the different species in an area to give a
measure of biodiversity. You can then communicate ideas to scientists over the world about
which areas of the world need conserving. If we did not use the binomial system, these
organisms would not be as easily identified and areas of the world may not be conserved –
meaning species may go extinct.
Biodiversity is important because we rely on living things for food, medicines and many other
products. The more species there are in the world the more possible products available to us (a
possible cure for cancer). If we do not use binomial system, we may not conserve the correct
places and these products will not be available to us.
The binomial system is important in these types of conservation projects as it can be used to
identify and study the species at threat, deciding which need to be conserved, and then putting
the conservation into place. This should help species to survive and not go extinct.
If it is used to help conserve areas such as the Tropical Andes then eventually we may discover
more and more species and get different cures for diseases etc.
1.9 Explain how accurate classification may be complicated by:
a variation within a species
• Sometimes organisms of the same species
look very different but are the same species
(eg humans, dogs).
• Sometimes different species look exactly alike
but are different species (meadowlark).
HIGHER STUFF: Why is classification of
organisms sometimes difficult.
1.9 Explain how accurate classification may be complicated by: H
H
b hybridisation in ducks
H
c ring species
HIGHER STUFF: b. Hybridisation in Mallard
ducks
Hybridisation (where two similar species interbreed to
produce a hybrid).
Mallard ducks can hybridise with other closely related
species of duck to produce fertile hybrid duck offspring.
These hybrid offspring then breed with other hybrids,
Mallards or other duck species producing ducks with a
continuous range of characteristics, rather than separate
species. This makes classification of them difficult.
HIGHER STUFF: c. Ring species
• The Larus gulls interbreed
in a ring around the arctic.
• Ring species as shown
below is where
populations of the same
species can interbreed
with neighbouring
populations. For instance
the Larus gulls at number
4 may interbreed with the
neighbouring populations
at number 3 and 5.
• However the two
populations at the ends (1
and 7) cannot interbreed.
• It is hard to divide ring
species into separate
species which sometimes
makes classification
difficult.
Ready to learn starter: A scientist has
discovered something new.
How can this discovery be validated?
1.19 Explain the role of the scientific community in validating new
evidence, including the use of:
a scientific journals
b the peer review process
c scientific conferences
Validating new evidence
If a scientist discovers something new how can we believe them?
They will: Write a paper detailing their method and results. This will then
be peer reviewed (other scientists assess it to see if it is any good).
It may then be published in a scientific journal if it is good enough.
He may discuss his study and results at a scientific conference.
Other scientists may then decide to repeat the study to see if they find
the same thing.
1.10 Construct and use keys to show how species can be identified
Using keys to identify organisms
• This is a
branching key
Grade C:
Can you use yes / no keys to
identify organisms
Grade B: Can you Establish how to
use yes / no and statement keys to
identify organisms
Grade A – A*:
Can you Design a simple key to
identify 8 organisms
Ready to learn starter: Variation questions
• What is variation?
• What are the two types of variation and give
examples.
• What are the causes of the two types of
variation?
• What kinds of graphs show each type of
variation?
1.13 Describe variation as continuous or discontinuous
We call the differences between organisms …
The two types of variation are : Continuous and
Discontinuous variation
Continuous variation = can be a range of values or measurements
eg height, weight
Discontinuous variation = Fits into certain categories eg blood
group, hair colour, shoe size.
ALL: State what is meant by variation, and
(Grade E) conduct an investigation into
variation. (SKILL) Describe variation as
continuous or discontinuous and give
examples. (Grade D)
MOST: Establish
what causes
variation within
species. (Grade C)
SOME: Interpret
variation graphs
using normal
distribution curves
(Grade B)
FEW: Perform
calculations based on
graph information
(Grade A-A*)
Continuous / Discontinuous variation
Continuous variation = can be a range of values or
measurements eg height and weight
Discontinuous variation = Fits into certain categories eg
blood group, gender, eye colour
ALL: State what is meant by variation, and
(Grade E) conduct an investigation into
variation. (SKILL) Describe variation as
continuous or discontinuous and give
examples. (Grade D)
MOST: Establish
what causes
variation within
species. (Grade C)
SOME: Interpret
variation graphs
using normal
distribution curves
(Grade B)
FEW: Perform
calculations based on
graph information
(Grade A-A*)
What causes variation?
Variation is caused by :
1. Discontinuous variation is are inherited variation.
Features passed on from parents sexually reproducing and
passing on genes.
Features obtained by mutation – a change in the DNA.
2. Continuous variation is caused by a combination of genes and
environment. This means features that are affected by the
surroundings. For example, height and weight are both genetic
and affected by your diet / illness.
ALL: State what is meant by variation, and
(Grade E) conduct an investigation into
variation. (SKILL) Describe variation as
continuous or discontinuous and give
examples. (Grade D)
MOST: Establish
what causes
variation within
species. (Grade C)
SOME: Interpret
variation graphs
using normal
distribution curves
(Grade B)
FEW: Perform
calculations based on
graph information
(Grade A-A*)
1.16 Describe the causes of variation, including:
a genetic variation – different characteristics as a
result of mutation or reproduction
b environmental variation – different characteristics
caused by an organism’s environment (acquired
characteristics)
next
1.15 Interpret variation graphs using normal distribution curves
Continuous
variation
This graph shows a normal distribution graph (bell shaped
curve). It shows continuous variation such as height or
weight.
Continuous variation is caused by a mixture of genes and the
environment and are known as acquired characteristics.
Most people fall into the centre of the graph. Very few people
fall at the extreme ends.
Discontinous
variation
• Goes into categories – will show a bar chart with no
particular pattern. This graph shows discontinuous
variation which is caused by genes (parents sexually
reproducing or a mutation – a change in the DNA).
1.11 Explain how organisms are adapted to their environment and
how some organisms have characteristics that enable them to
survive in extreme environments, including deep-sea
hydrothermal vents and polar regions
Adaptations!!!
Adaptations are features
that help an organism
survive in its
environment!
Extreme environments
Arctic
vs Hydrothermal vents
Extremely cold
Extremely Hot
Slippery ice
Very little or no light so no
photosynthesis
Lots of snow
High pressure
Temperature can be
-40 degrees
Acidic environment and toxic
hydrogen sulphide
Large feet which enables
them to
Small ears to
Thick layer of blubber
under skin for
Black skin to
White fur for
Rough pads on feet to
Thick fur for
Polar bear
spread weight to stop them sinking in
the snow – also for swimming
conserve heat
insulation and energy reserves
absorb heat
camouflage
grip the ice.
insulation
Pompeii Worm
Shell or tough body that is adapted to high pressures
conserve energy (doesn’t need them, it’s
No eyes to
too dark.)
Sensitive tentacles to
sense the environment
Spends a lot of time in a
hide from predators
tube to
Body covered in thick layer protect it from the heat
of bacteria to
Tube worm – This is different to a pompeii
worm.
Tubeworms have bacteria that live inside them that convert
hydrogen sulphide compounds (from the vents) into food for
the tube worms.
In return the tubeworm provides oxygen / protection for the
bacteria.
This is an example of mutualism.
(mutualism is the way two organisms
exist in a relationship in which each
benefits)
ALL: Can you give
examples of ‘extreme
environments’ and
outline why they are
‘extreme’. (Grade C)
MOST: Establish
the adaptations
of a polar bear
and pompeii
worm. (Grade B)
FEW: Can you explain in detail how the adaptations of a polar bear and
pompeii worm allow them to live in these environments.
(Grade A)
FEWER: Consider how tube worms feed by chemosynthesis and how
bacteria assist with this, and how this is an example of mutualism. (Grade
A*)
Evolution
1.12 Demonstrate an understanding of Darwin’s theory of evolution by natural selection including
a variation
b over-production
c struggle for existence
d survival of the fittest (natural selection)
e advantageous characteristics inherited
f gradual change (evolution)
The 6 main stages of evolution.
1. An animal may have lots of babies (over
production)
2. These will all be different (variation)
3. There will be competition for survival (food,
water, shelter, escape from predator).
4. The “weaker” or less adapted ones die whilst the
ones that have the best characteristics will survive.
(Survival of the fittest or natural selection)
5. These will breed and pass on the genes for these
characteristics.
6. This leads to a gradual change in the species over
time (evolution)
Hedgehog example
• Example: How the hedgehog got its spines
• Several million years ago a species of mammal had long, thick hair.
However, some of the mammals had soft hairs and some had stiffer hair
than others (variation)
• The mammal had about 6 pups at a time (overproduction).
• More pups meant competition for survival. (For space, water , food or
escape from predators).
• A new predator entered the area in which the mammal lived.
• The predator avoided eating the mammals with the stiffer hair and ate
more of the ones with softer hair. (Competition for survival). So, the
mammals with softer hair died out. The ones with the stiffer hair survived.
• The ones with the stiffer hair had the good feature that helped it to survive
(it was the best adapted). (Survival of the fittest or natural selection).
These were able to breed and pass this characteristic onto their offspring.
(Breeding and passing on genes).
• Over thousands of years, the mammals with the stiffest hairs were the most
likely to survive and gradually this became a species of mammals with
spines. The hedgehog. (Evolution or gradual change).
EXTINCTION
• 1. Sudden change in an organisms environment
(This may be due to climate change, lack of food, a
new predator, loss of habitat).
• 2. None of them have adaptations to help them
survive.
• 3. They start to die they may all go extinct.
Ready to learn starter: Can you recall and
explain the evidence for Darwin?
There are 5 main pieces of evidence for Darwin’s Theory of evolution
by natural selection.
These are:
Fossil Record
DNA evidence
Peppered moth
Resistant rats
Speciation
Can you summarise each piece of evidence and explain how it
supports Darwins theory?
Evidence for Darwin
•
1.18 Explain how evidence from DNA research and the emergence of resistant organisms support Darwin’s theory.
Evidence for Darwin includes:
Peppered Moth: Before the industrial revolution the pale moth was camouflaged and so there were lots of
these. There were very few dark moths which were not camouflaged and got eaten by birds. After the
industrial revolution lots of smoke went on the trees, camouflaging the dark moths and showing up the
pale moths which started getting eaten more. The dark moths survived, bred and passed on their gene
for the dark wings to their offspring. Over time the numbers of dark moths increased and the numbers
of pale moths decreased.
Resistant rats and bacteria: A mutation has led to a rat being resistant to rat poison (warfarin). Warfarin will
kill the non-resistant rats. The resistant rats survive, pass on the resistant gene to their offspring. Over
time the numbers of warfarin resistant rats go up, the numbers of non-resistant rats go down (and will
possibly become extinct one day).
DNA evidence: All living things on our planet use DNA as their instruction manual. This suggests all life is
related, just as we expect from Darwin’s theory. When you do this you can compare the DNA of lots of
different living creatures. Amazingly, you find some of the same chunks of DNA in bacteria as in humans.
Speciation : The formation of two different species from one original species. Eg the finches on the
Galapagos islands. Originally the finches on two different islands were the same species, but all showed
variation in their beak size (some had fatter beaks and some had thin beaks). On one island there were
lots of nuts. The fat beaked bird survived as they could crack and eat the nuts. They could then breed
and pass on the fat beak gene to their offspring. Thin beaked birds died. Over time all birds on this island
had fat beaks.
On the other island there were lots of insects. The thin pointy beaked bird survived as they could get in the
holes to eat the insects. They could then breed and pass on the thin beak gene to their offspring. Fat
beaked birds died as they could not get the insects. Over time all birds on this island had thin beaks.
Eventually the birds on each island become so different that they will become two separate species
(speciation) and will not interbreed.
Fossil Record: The fossils discovered show slight changes in species over time, supporting Darwin.
Genes – where are they?
1.20 Describe the structure of the nucleus of the cell as containing chromosomes, on
which genes are located
1.21 Demonstrate an understanding that genes exist in alternative forms called
alleles which give rise to differences in inherited characteristics
Genes are on the chromosomes.
Chromosomes are found in the nucleus
of a cell – as shown on the next slide.
Nucleus
Cell membrane
Cytoplasm
Full set f 23 pairs of
chromosomes
1 chromosome
Gene
Chromosomes
in nucleus
Base pairs
A strand
of DNA
Can you summarise what each part does and give the
order do they go in from largest to smallest
The three main parts of an animal cell are cell membrane,
cytoplasm and nucleus.
In the nucleus of each cell there are 46 chromosomes – 23
pairs. 23 inherited from mum, 23 inherited from dad.
Each chromosome sometimes looks like an X shape – it is
thread like and made up of coiled DNA and divided into
many genes.
A gene is a section or strand of DNA that contains
instructions for making a specific protein. This protein may
be for hair colour etc.
DNA is made up of 4 different bases that form the unique
code that makes you you!
Grade E
Can you state
where the
genetic
information is
found in a cell.
Grade D
Can you label a
diagram (model) of
the structures that
are involved in
inheritance.
Grade C
Can you label a diagram (model) of
the structures that are involved in
inheritance and make use of the
information to summarise each
part.
Grade B
Can you determine how
the structures link
together. HOT
Ready to learn starter: Can you define
the following genetics keywords.
Gene
Allele
Genotype
Phenotype
Homozygous
Heterozygous
Dominant
Recessive
Genetics words
1.22 Recall the meaning of, and use appropriately, the terms: dominant, recessive, homozygous,
heterozygous, phenotype and genotype
Gene
Strand of DNA. Codes for a protein that may give you your eye
or hair colour.
A different or alternative version of the same gene.
Allele
The alleles you actually have for a characteristic.
Genotype
Physical characteristics
Phenotype
Homozygous
Matching alleles e.g. HH or hh
Heterozygous
Different alleles, e.g. Hh.
An allele represented by a capital letter. Even if you only have
one of these, you will have this characteristic.
An allele represented by a lower case letter. You need both of
these alleles to have this characteristic.
Dominant
Recessive
Different versions of genes
Here the gene that is shown codes for petal colour – it is the same gene.
gene for
petal colour
gene for
petal colour
version for red
petals
version for
yellow petals
Each chromosome may have a different version
of a gene.
Different (or alternative) versions of a gene are
called alleles.
Inheritance
Therefore sperm have 23 chromosomes which fuse with 23
chromosomes in the egg at fertilisation so that the fertilised egg
has 46 chromosomes – the normal amount for a human.
Punnet squares – probabilities,
percentages and ratios
1.23 Analyse and interpret patterns of monohybrid inheritance using a genetic diagram and
Punnett squares
1.24 Calculate and analyse outcomes (using probabilities, ratios and percentages) from
monohybrid crosses
Ready to learn starter:
Normal = F Cystic fibrosis = f
Ff
Ff
Complete the punnet square correctly.
Then give the probability that these people could have a
cystic fibrosis child.
What percentage of their children could be carriers of the
cystic fibrosis allele?
What is the ratio of normal to cystic fibrosis children?
Tallness T = tall t = short
T T
T t
T
T
T
TT
TT
t
Tt
Tt
Probability = number out of four.
So will be either 0/4 ; 1/4 ; 2/4; 3/4 or 4/4
The probability of having a tall child is 4/4
Tallness T = tall t = short
T T
T t
T
T
T
TT
TT
t
Tt
Tt
Percentage = number out of hundred.
So will be either 0% ; 25% ; 50%; 75% or 100%
The percentage of tall children is 100%
Tallness T = tall t = short
T T
T t
T
T
T
TT
TT
t
Tt
Tt
Ratio = number that have the trait compared with
them that dont. 4:0 ; 3:1 ; 2:2 ; 1:3 ; 0:4. (Will
always add up to four!)
The ratio of tall children to short children is 4:0
1. Explain why both of the parents had brown eyes.
2. Were the parents heterozygous or homozygous?
3. Explain why the two brown eyed parents have been able to produce a blue eyed child. Use a
punnet square to help with your explanation.
4. 4. If one of the parents was homozygous dominant for brown eyes, explain whether they
could produce blue-eyed offspring.
Keywords: heterozygous homozygous
dominant
recessive
offspring
alleles
gene offspring
See next slide
Model answer to previous slides questions
1.
2.
3.
Both parents have brown eyes as they must have at least 1 dominant gene each
for brown eyes.
The parents must be heterozygous (Bb) because they have got a blue eyed child,
so both parents must have a recessive blue eyed allele to pass down to the blue
eyed child as you need two recessive alleles to be blue eyed.
The brown eyed parents are carriers of the blue eyed allele. You can only be
blue eyed if you inherit two recessive alleles from your parents, therefore each
parent has passed down this allele to the blue eyed baby. A punnet square to
show this would be:
B
b
B
BB
Bb
b
Bb
bb
Blue
eyed
baby
4. If a parent was homozygous dominant their genotype would be BB. They would only be able
to pass a dominant gene to their offspring, so therefore all offspring would have brown eyes,
as they would inherit at least one dominant allele.
B
B
B
BB
BB
b
Bb
Bb
All
brown
eyed
Ready to learn starter: What are the three
main symptoms of cystic fibrosis?
• Can you explain why these symptoms occur?
Genetic disorders
1.25 Describe (and explain) the symptoms of the genetic disorders:
a sickle cell disease
b cystic fibrosis
Ready to learn starter: What are the three
main symptoms of sickle cell disease?
• Can you explain why these symptoms occur?
Sickle Cell Disease Symptoms
Breathlessness
Pain (called crisis)
Tiredness
This happens because... sickle blood
cells block blood vessels in the lungs.
This happens because... Sickle-shaped
blood cells stick together and can block
blood vessels (called a crisis and
normally in joints)
This happens because... sickle blood
cells cannot carry as much oxygen to
cells, leading to less respiration and so
less energy.
ALL: Outline some symptoms of cystic fibrosis and sickle cell disease. (Grade D)
MOST: Establish why the symptoms of cystic fibrosis and sickle cell disease happen.(Grade C)
SOME: Solve, analyse and interpret punnet square and family pedigree diagram problems (Grade B)
HIGHER STUFF: Pedigree Analysis: What is
it?
This is where doctors may study family pedigree charts to
assess the probability that a couple may pass on (or may
have already passed on) a genetic disorder to their child.
Basic Symbols
ALL: Outline some symptoms of cystic fibrosis and sickle cell disease. (Grade D)
MOST: Establish why the symptoms of cystic fibrosis and sickle cell disease happen.(Grade C)
SOME: Solve, analyse and interpret punnet square and family pedigree diagram problems (Grade B)
More Symbols
ALL: Outline some symptoms of cystic fibrosis and sickle cell disease. (Grade D)
MOST: Establish why the symptoms of cystic fibrosis and sickle cell disease happen.(Grade C)
SOME: Solve, analyse and interpret punnet square and family pedigree diagram problems (Grade B)
• What does this show (see next slide)
This shows that Richard and Diane who are a couple, have had two children
(Michael and Brian). Brian has cystic fibrosis but both his parents are normal
(as they both have a dominant normal allele). His parents are both carriers
of the cystic fibrosis allele, and both have passed this down to Brian.
Sam has a 50% chance of having cystic fibrosis because his mum is a carrier
of the allele.
C
c
c
Cc
cc
c
Cc
cc
2/4 will have cystic fibrosis
This is 50%
2:2 (For every 2 normal children
there will be 2 cystic fibrosis
children.
HIGHER STUFF: Pedigree Analysis –
why do it?
H 1.26 Evaluate the outcomes of pedigree analysis when screening for genetic disorders:
a sickle cell disease
b cystic fibrosis