GCSE Biology Inheritance, Variation & Evolution

1. 15/01/2023
15/01/2023
Inheritance, Variation
and Evolution
AQA 2016 Biology topic 6
W Richards
Education Using
PowerPoint

2. 6.1 Reproduction
15/01/2023

3. 15/01/2023
Sexual Reproduction
The human egg
and sperm cell
contain 23
chromosomes
each.
When fertilisation happens the
gametes fuse together to make a
single cell containing 46 chromosomes
(23 pairs) - it contains information
from each parent. The same happens
in plants with pollen and egg cells.
We have similar characteristics to our parents due to genetic
information being passed down in genes through gametes:

4. 15/01/2023
Fertilisation summarised
Egg
Sperm
Fertilisation
23 chromosomes
in here
23 chromosomes
in here
46 chromosomes
in a fertilised
egg

5. 15/01/2023
Cell growth 1 - Mitosis
Each daughter cell has
the same number of
chromosomes and genetic
information as the parent
– a “clone” is produced.

6. 15/01/2023
Gamete formation - Meiosis
1) A copy of the genetic information is made
2) The cell divides twice to form four gametes,
each with a single set of chromosomes
All gametes are genetically different from each other.
Gametes will then join at fertilisation to restore the full
number of chromosomes and divides by mitosis from then on.

7. 15/01/2023
Mitosis vs. Meiosis
Mitosis:
1. Used for growth and repair of
cells
2. Used in asexual reproduction
3. Cells with identical number of
chromosomes and genetic
information are produced
(“clones”)
Meiosis:
1. Used to produce haploid
gametes for sexual
reproduction
2. Each daughter cell has half the
number of chromosomes of the
parent
During meiosis copies
of the genetic
information are made
and then the cell
divides twice to form
four daughter cells.

8. 15/01/2023
Sexual vs. Asexual reproduction
Sexual reproduction:
•2 parents are needed
•Offspring will have “pairs” of chromosomes
•This will cause genetic variation
Asexual reproduction:
•Only 1 parent needed
•Offspring are GENETICALLY IDENTICAL to
parent (“clones”)
“Snuppy” – the
first cloned dog
(Aug 05)

9. Sexual vs asexual reproduction (Bio only)
15/01/2023
Advantages of sexual
reproduction
Advantages of asexual
reproduction
No need to
find a mate
More time
and energy-
efficient
Increased
variation,
which may
cause an
evolutionary
advantage
Selective breeding can
be used to increase
food production
Which form of
reproduction is
better?
Faster than sexual
reproduction
Produces a clone of
a good animal

10. Reproducing Sexually and Asexually
15/01/2023
Some organisms can reproduce using both methods. Some
examples:
The malaria parasite reproduces
asexually in a human but
sexually in a mosquito
Many plants reproduce sexually but
can also reproduce asexually by
runners (e.g. strawberries) or by bulb
division (e.g. daffodils)
Fungi can reproduce asexually using
spores or sexually to give variation

11. 15/01/2023
Genes
Section of a chromosome:
Genes for
eye colour
Genes for
hair colour
Genes for
blood group:
Genetic information is stored by genes which are arranged on
chromosomes:
Each gene codes for a particular sequence
of amino acids, to make a specific protein.
The entire genetic makeup of an organism
is called its genome.

12. 15/01/2023
Genes, Chromosomes and DNA
DNA is a polymer made up of two strands forming a “double
helix” structure. DNA is contained within chromosomes.

13. 15/01/2023
The Human Genome Project
In 1990 an international project was launched called the
“Human Genome Project”. The aim was to map the _______
makeup of the human race and includes work from ______ in
18 different countries.
Possible benefits:
• Improved genetic testing
• Improved predictions and screening of ________ diseases
• New gene ________ treatments
• New knowledge of human _______ patterns from the past
Words – scientists, genetic, migration, inherited, therapy

14. 15/01/2023
Some facts:
- It is made of four different nucleotides that consist
of a _____ and phosphate group
- It contains instructions on what a ____ does, how
the organism should work etc
- The code is made up from the four ____ that hold
the strands together with weak hydrogen bonds
- A sequence of three bases represent the order in
which _____ acids are assembled to make specific
________
- The DNA polymer is made up of repeating
________ units
- In the complementary strands, a C is always linked
to a G and a T is always linked to an A
DNA detail (Bio only)
Words – amino, sugar, bases, cell, proteins, nucleotide

15. 15/01/2023
Making proteins (HT only)
1) DNA “unravels” and a copy of one strand is
made
2) The strand copy is made to produce RNA
3) The mRNA copy (with its code) then
moves towards the ribosome
4) The ribosome “decodes” the mRNA code
which tells the ribosome how to make the
protein
5) Amino acids are then joined together to
form a polypeptide (protein)

16. 15/01/2023
Mutations (HT only)
Cells contain a nucleus and the nucleus contains genes that
carry instructions for what that cell should do:
Genes
Some facts:
• Some genes are “switched off” and don’t do
anything in that cell
• Genes basically tell the cell which proteins they
should be producing
• Sometimes cells can “mutate” which may have a
harmful effect on the cell and can be caused by
natural or artificial means.

17. Genetic mutations (Bio HT only)
15/01/2023
A T C G G A T
Here’s a sequence of bases in DNA:
Q. What happens if this sequence is changed?
Possible ways this sequence is changed:
1) A base is inserted A T C G G A T
A
2) A base is substituted A T C G G A T
A
3) A base is deleted A T C G G A T
DNA mutations are the reason why we have genetic variation in the first
place. Sometimes these changes won’t affect a protein made from the
DNA, sometimes the protein may function differently (changing the
phenotype). Changes in non-coding DNA may influence phenotype by
altering how genes are expressed.

18. 15/01/2023
Proteins (HT only)
Proteins, when unfolded, are basically long chains of amino
acids:
Every different protein has its own number and sequence of
amino acids which results in differently shaped molecules with
different functions.
Some example proteins:
Name of protein Function
Collagen Give structure
Insulin Hormones
Enzymes Help food digestion
Not all parts of DNA code for proteins. Non-coding parts of
DNA can switch genes on and off.

19. 15/01/2023
Mutations and effects on Proteins (HT)
Enzymes are biological catalysts. Most enzymes are proteins
and, as such, a mutation in DNA will affect them:
An enzyme is basically a protein molecule
made up of long chains of amino acids. These
molecules are then “folded” to create a
certain shape with high “specificity”:
The enzyme’s shape helps another
molecule “fit” into it:
This shape can be affected by
mutations in the DNA or the
proten may lose its strength:
Enzyme Substrate

20. 15/01/2023
Basic genetics - Boy or Girl?
X Y X
XX XY
Girl Boy
“Allele”
“Phenotype”
Heterozygous Homozygous
Note that the Y
chromosome is “dominant”
and the X is “recessive”.
The Y chromosome dictates
the development of testes.

21. 15/01/2023
Father
Mother
Son
Daughter
Boy or Girl?
During sexual
reproduction,
children
inherit two
alleles of each
gene (one from
each parent).

22. 15/01/2023
15/01/2023
Key words
Genotype
Phenotype
Allele
Dominant
Recessive
Homozygous
Heterozygous
•This allele determines the development of a
characteristic
•The characteristic caused by the genotype
•This allele will determine a characteristic only if
there are no dominant ones
•This word refers to a pair of chromosomes being
made of two different alleles of a gene
•The genetic make up in a nucleus
•This word refers to a pair of chromosomes being
made of two of the same alleles of a gene
•An alternative form of a gene

23. 15/01/2023
Eye colour
In eye colour the brown eye allele is dominant, so we call it
B, and the blue eye is recessive, so we call it b:
bb
BB Bb
Homozygous
brown-eyed
parent
Heterozygous
brown-eyed
parent
Blue-eyed parent
What would the offspring have?

24. 15/01/2023
Eye colour
Example 1: A homozygous
brown-eyed parent and a blue-
eyed parent:
Example 2: 2 heterozygous
brown-eyed parents
BB bb
X Bb Bb
X
Parents:
Gametes:
Offspring: Bb Bb Bb
Bb BB Bb bb
bB
B B b
b B b
B b
(FOIL)
All offspring have brown eyes 25% chance of blue eyes

25. 15/01/2023
Eye colour
Example 3: A
heterozygous
brown-eyed
father and a
blue-eyed
mother:
Bb
Bb Bb bb
bb
bb
b b
B b
Equal (50%)
chance of
being either
brown eyed or
blue eyed.
Note – in reality, characteristics like this are usually depend
on the instructions of multiple genes and other parts of the
genome.

26. 15/01/2023
B b
b
b
Another method – the “Punnett square”
Example 3: A heterozygous brown-eyed
father and a blue-eyed mother:
B b
b Bb bb
b Bb bb
Father
Mother

27. 15/01/2023
Example questions
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).

28. 15/01/2023
Inherited diseases
1) Cystic fibrosis – a disorder or cell membranes. It’s caused
by recessive alleles so both parents need to be “carriers”:
2) Polydactyly – a condition where a person has extra fingers
or toes. It’s caused by a dominant allele so can be passed on
by a parent who already has it:
Embryos can be screened for alleles that cause these
diseases before birth. Do you think this is right?
Ff Ff
X
Pp pp
X

29. 15/01/2023
Genetic Diagrams
Here’s what happens (genetically) when an egg is fertilised:
xx
xx xy xy
xx
xy
x y
x x
Equal (50%)
chance of
being a boy or
a girl
Mother Father

30. 15/01/2023
x y
x
x
Genetic Diagrams
Here’s another way of drawing it:
Father
Mother

31. 6.2 Variation and Evolution
15/01/2023

32. 15/01/2023
Variation
“Variation” is the name given to differences between
individuals of the SAME species.
Variation is due to GENETIC or ENVIRONMENTAL causes.
There is often extensive variation within a species. For
example, consider dogs:
1) Ways in which they are the
same:
2) Ways in which they are
different:

33. 15/01/2023
Environmental differences
Some of this variation is due to our parents, but some of it is
due to our upbringing and the environment in which we live –
this is called “Environmental variation”.
Variation due to
inheritance only
Variation due to
environment only
Variation due to a
bit of both

34. 15/01/2023
15/01/2023
Beneficial Mutations - the
peppered moth
All variations arise from mutations. Most mutations have no
effect on phenotype whereas some do. If the new phenotype
is more suited to its environment then it can lead to a rapid
change in the species. For example…

35. 15/01/2023
15/01/2023
Evolution
Charles Darwin,
1809-1882
Evolution is the slow change in
organisms that happens over
a long period of time. All
life on Earth has evolved
from simple life forms that
existed around 3 billion
years ago. It happens
through a process called
“natural selection”, which
basically says this:
3) They then have
kids who also have
the “better”
phenotypes
1) Different
species show
variation
2) The “better
adapted” ones
survive

36. 15/01/2023
15/01/2023
Definition of “Species”
Liger
Geep
Zebroid
Mule
Different species can sometimes mate and have offspring but they would
be infertile. Some examples:
A “species” is defined as when organisms reproduce with each other to
produce fertile offspring.

37. 15/01/2023
Selective breeding
I raise cows. Each type of
cow is good at a certain job.
The Friesian cow produces
large quantities of milk, the
Jersey cow produces very
nice milk and the Hereford
cow produces lot of beef.
If, for example, I want lots of milk
I would only breed Friesian cows
with each other – this is
SELECTIVE BREEDING. The only
trouble is that I’m reducing the
“gene pool” by doing this.
Friesian
Jersey
Hereford

38. 15/01/2023
Examples of Selective Breeding
Other examples can include plants with larger flowers and disease
resistance in crops. Some breeds may be particularly prone to diseases or
inherited defects due to selective breeding.

39. Basics of Genetic Engineering
With genetic engineering I can
produce milk that contains:
• Extra protein
• Lower levels of cholesterol
• Human antibodies
Genetic engineering is basically the idea of modifying a
genome using a gene from a different organism in order to
improve characteristics. For example:
Genetic Engineering has also been used
to make disease-resistant plants with
bigger fruits and to produce insulin on
large scales.

40. 15/01/2023
Genetic Modification
Advantages Disadvantages
Improving crop yield
Improving resistance to
pesticides
Extend shelf-life
Manufacture a certain
chemical (e.g. insulin)
Convenience
Current medical research
into using genetic
modification to overcome
inherited disorders
Genetically modified
organisms may be expensive
Need for long term studies
Effects may be passed on to
other crops, e.g. weed
resistance spreading from
crops to weeds

41. Summary
Here are the basic steps:
Identify the desired gene
Remove the gene from the DNA
Cut open the DNA in the other
organism
Insert the removed gene using
enzymes again
Clone the organism to produce lots
of copies

42. 15/01/2023
How Genetic engineering is done (HT only)
Step 1: “Cut out” the part of the human
chromosome that is responsible for the
desired characteristic.
Step 2: Using another restriction enzyme cut
open a ring of bacterial DNA (a “plasmid” or
“vector”). Other enzymes are then used to
insert the piece of human DNA into the plasmid.
Most of the cells don’t take up the vector so
the ones that have need to be “marked”.
Step 3: Place the plasmid into a bacterium
which will start to divide rapidly. As it
divides it will replicate the plasmid and
make millions of them, each with the
desired characteristic.

43. 15/01/2023
15/01/2023
Cloning Plants (Bio only)
Plants can reproduce ASEXUALLY. The offspring are
genetically ________ to the parent plant and are called
_________. The only variation between then will be due to
environmental factors. Two examples:
1) This spider plant has grown a rooting
side branch (“stolon”) which will
eventually become __________.
2) A gardener has taken cuttings of
this plant (which probably has good
characteristics) and is growing them
in a ____ atmosphere until the
____ develop.
Words – clones, damp, independent, roots, identical

44. 15/01/2023
15/01/2023
Cloning Plants by tissue culture (Bio only)
1) Scrape off a
few cells from
the desired plant
2) Place the scrapings
in hormones and
nutrients
3) 2 weeks later
you should have
lots of genetically
identical plants

45. 15/01/2023
Cloning Animals 1 (Bio only)
Method 1 – “Embryo transplants”
A developing embryo is “split” before the cells specialise and
the identical embryos are implanted into host mothers.

46. 15/01/2023
Cloning Animals 2 (Bio only)
Method 2 – Fusion:
Animals can be cloned by taking the nucleus from an adult body cell and
transferring it to an empty, unfertilised egg and giving it an electric shock
to stimulate the egg to form an embryo:
Host mother Clone

47. 6.3 The Development of understanding
of Genetics and Evolution
15/01/2023

48. 15/01/2023
15/01/2023
Evolution (Bio only)
Charles Darwin,
1809-1882
Evolution is the slow change in
organisms that happens over a long
period of time. All life on Earth
has evolved from simple life forms
that existed around 3 billion years
ago. I came up with this theory
after observations around the
world and after years of
experimentation and observations.
Evolution happens through a
process called “natural selection”,
which looks like this:

49. 15/01/2023
15/01/2023
Natural Selection (Bio only)
1) Each species shows variation –
here are some long-necked
giraffes and short-necked
giraffes:
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. The “smaller-
necked” giraffe will eventually die out.
Get off
my land
Harsh
Yum
3) The “better adapted” members
of these species are more likely
to survive – “Survival of the
Fittest”

50. Controversy about Darwin’s Work (Bio only)
15/01/2023
I published my work
“On the Origin of
Species” in 1859.
However, it attracted
a lot of controversy
because:
1) It challenged the theory that God made
every animal and plant on the Earth
2) There wasn’t a lot of evidence at the time
3) The mechanism of natural selection was
not known until around 50 years later

51. 15/01/2023
An example of Natural Selection –
antibiotic resistant bacteria
1) Mutation – some strains of
bacteria can develop _______
to the antibiotics.
2) The non-resistant bacteria
are _____ by the _______.
3) The resistant bacteria
_______ and pass on their
mutations to their ______ -
an example of ______
______
Bacteria
Penicillin
No
effect!!
Words – offspring, resistance,
killed, antibiotics, reproduce,
natural selection

52. 15/01/2023
Darwin vs Lamarck
Darwin wasn’t the first to come up with evolution – he was
simply the one credited with explaining how it worked (i.e.
Natural Selection). An earlier scientist called Lamarck
explained evolution by different means:
Jean Baptiste
Lamarck
(1744 - 1829
The giraffe has a long neck
because it “stretches” its neck to
reach the food, and these long
necks are passed on to their
offspring. Organs which aren’t
used will eventually disappear.
However, we now
know that changes
like these cannot be
inherited.

53. Speciation (Bio only)
15/01/2023
Alfred Wallace
1823-1913
I independently proposed the theory of
evolution by natural selection at around
the same time as Darwin. I am best
known for my work on warning colours in
animals and my theory of speciation – the
“formation of a new species”. One
example of speciation is “geographic
isolation”:

54. 15/01/2023
Geographic Isolation
Different species can be formed by “geographic isolation”, for example,
consider an African elephant:
1) Elephants are separated by a
geographic feature e.g. a _________
2) Elephants on each side of the
mountain have different ______ in
their _____ pool
3) Some offspring have characteristics
that help them survive
4) Their weaker _______ die out and
the offspring are so genetically
removed that they’re incapable of
________ with each other – they’re
now different ________
Words – species, mutations, mountain, gene, ancestors, reproducing

55. 15/01/2023
Mendel’s Work (Bio only)
Guten tag! My name is Gregor Mendel. I
am the father of modern genetics because
of the work I did on pea plants in 1865…
Take two plants; one which is
pure-bred for tallness and one
pure-bred for shortness, and
cross them:
X
Mendel’s experiment:

56. 15/01/2023
Modern Genetics
All the plants produced
were tall.
Now cross two of these plants…
3 out of every 4 plants
were tall, leading Mendel
to hypothesise that “for
every characteristic
there must be two units
that determine the
characteristic”

57. 15/01/2023
Modern Genetics
Achtung! Unfortunately, nobody knew
about chromosomes or genes when I
published my findings so no one believed
me until after my death, when more
powerful microscopes were available.
Three key developments that led to Mendel’s ideas being accepted:
1) By the late 19th Century behaviour of chromosomes during cell division
had been observed
2) By the early 20th Century it was observed that chromosomes and
Mendel’s “units” behaved in similar ways – therefore, the units (now
called genes) are located on chromosomes
3) In the mid-20th Century the structure of DNA was determined.

58. 15/01/2023
Evidence for Evolution
Fossil records, showing the
development of an organism
over a long period of time
Antibiotic-resistant
bacteria, giving evidence
for natural selection
Now that the mechanism of natural selection has been
understood and with evidence like fossils and antibiotic-
resistant bacteria, the theory of evolution is widely accepted.

59. 15/01/2023
Fossils
Fossils are the remains of organisms from millions of years ago and are
found in rocks. They provide evidence of early life and could have been
formed in many ways. Four examples:
This fossil of a bat
was formed due to
hard parts of the
animal not decaying
This bee and orchid
pollen were preserved
in amber – the amber
lacked some of the
conditions needed for
decay to happen
This fossil was formed by
parts of its body being
replaced by minerals
Fossilised footprints

60. 15/01/2023
Fossil records
Fossil records can provide a useful way of observing a species’
development:
The problem is, many early forms of life only had soft bodies
and the few remaining traces of them have been destroyed by
geological activity. This makes it difficult for scientists to
know what happened in the distant past.
The “Stenheim
skull”, found in
Germany in 1933
Oh
no…

61. 15/01/2023
Extinct Species
Dodo
Sabre-toothed tigers
and mammoths
“Extinction” is when every
member of a species dies out.
Some examples:

62. 15/01/2023
Extinction
Words to use: deforestation, competition, dinosaurs,
human, environment
Extinction can happen due to an organism’s
inability to adapt and die because of:
• Increased _______
• New predators
• Changes in the _________
• New diseases
Alternatively, a “mass extinction event” can
happen, for example the extinction of the
__________.
In modern days animals are in danger due to
_____ activity, e.g. pollution, hunting,
__________ etc…
Oh no…

63. 15/01/2023
Recap – antibiotic resistant bacteria
1) Mutation – some strains of
bacteria can develop _______
to the antibiotics.
2) The non-resistant bacteria
are _____ by the _______.
3) The resistant bacteria
_______ and pass on their
mutations to their ______ -
an example of ______
______
Bacteria
Penicillin
No
effect!!
Words – offspring, resistance,
killed, antibiotics, reproduce,
natural selection

64. 15/01/2023
Using Antibiotics
Antibiotics are used to cure
bacterial _______ by killing
infective bacteria inside the
body. The development of
new antibiotics is usually
slower than the development
of new ______ of bacteria.
There are some issues with using antibiotics:
1) Patients should always complete their _______
2) Antibiotics should be used _______ as bacteria can grow
_______ to them, e.g. the MRSA “superbug”.
3) Agricultural use of antibiotics should be _______
Words – course, immune, strains, diseases, sparingly, restricted

65. 6.4 Classification of New
Organisms
15/01/2023

66. 15/01/2023
15/01/2023
Classification
The world is populated by millions of different species of
animals and plants…

67. 15/01/2023
15/01/2023
Classification
How would you construct a key to classify these organisms?

68. 15/01/2023
15/01/2023
Classifying organisms
All organisms are classified into groups. For example:
Organism
Plants Animals
Vertebrates Invertebrates
Reptiles Fish
Birds
Amphibians
What is the
main difference
between these?
“Kingdoms”
Dogs Cats
“Species”
Mammals
Notice that the number of
similarities increases as
you go down this tree

69. 15/01/2023
Why use classification?
15/01/2023
Carolus Linnaeus, 1707-1778
I invented the modern system of naming
species. I did this so that species would
have the same name in every language and so
that we would have a greater ability to
understand different species and how they
have evolved.
Human –
“homo sapien”
Dog – “Canis lupus
familiaris”
Wasp – “vespula
germanica”

70. 15/01/2023
Classification
Organisms are classified using the following levels:
Kingdom
Phylum
Class
Order
Family
Genus
Species

71. 15/01/2023
Classification
Consider, for example, a dog:
Kingdom - Animalia
Phylum - Chordata
Class - Mammalia
Order - Carnivora
Family - Canidae
Genus - Canis
Species – C. lupus

72. 15/01/2023
The 5 Kingdoms
The 5 Kingdoms that organisms are classified by are:
Animalia
Plantae
Fungi
Protoctista
Prokaryotes
Multicellular, don’t have cell walls or chlorophyll
Multicellular, have cell walls and chlorophyll
Multicellular, have cell walls but no cholophyll
Unicellular, have a nucleus
Unicellular, have no nucleus

73. 15/01/2023
15/01/2023
Classification
A modern way of doing it…
As microscopes became more powerful
and our knowledge of DNA improved,
new models of classification were
proposed. Due to evidence from
chemical analysis I devised a “three-
domain” system:
Archaea (primitive bacteria usually living in extreme
conditions)
Bacteria (true bacteria)
Eukaryota (which includes protists, fungi, plants and animals)
Carl Woese, 1928-2012

74. 15/01/2023
Common Ancestors
Modern DNA research shows that all forms of life share a lot
of their DNA. This is used as evidence to suggest that all
forms of desecnded from common ancestors (the Theory of
Evolution).
98.8% shared DNA
85% shared DNA

75. 15/01/2023
The “Evolution Tree”
Family Hominidae
(Great Apes)
Family Hylobatidae
(Lesser Apes)
Subfamily
Hominidae
Subfamily
Ponginae
Tribe Homini
Tribe Panini
Tribe Gorillini
Humans
Chimpanzees Gorillas
Orangutans
Gibbons
Similar species are proposed to have common ancestors but
also will have differences due to the habitats they live in.
Scientists use current
classification data and
older fossil data to help
them develop this tree