Edexcell ppt Biology 3.13 - 3.33 Used in lessons to scaffold class teaching and as a revision resource for students

1. INHERITANCE
(Syllabus points 3.13 – 3.33)

2. REPRODUCTION (review)
3.1 understand the differences between sexual and asexual reproduction
There are two types of reproduction;
• Sexual: reproduction in which two gametes
(sex cells) fuse to create a new offspring that
is genetically different to the parents. Two
parents are involved.
• Asexual: reproduction without fusion of
gametes. It involves one parent only and
produces offspring that are genetically
identical to the parent (clones).

3. Fertilization (review)
3.2 understand that fertilisation involves the fusion of a male and female gamete to produce a zygote that
undergoes cell division and develops into an embryo
Definitions
• Fertilization:
• Zygote:
• Embryo:
A male and a female gamete fuse
to form a zygote
a cell that is the result of
fertilization. It will divide by mitosis
to form an embryo
An organism in its early stages of
development, especially before it
has reached a distinctively
recognizable form.

4. Fertilization, Zygote, Embryo(Review)
3.2 understand that fertilisation involves the fusion of a male and female gamete to produce a zygote that undergoes cell division and develops
into an embryo

5. Genes are on Chromosomes
3.13 understand that the nucleus of a cell contains chromosomes on which genes are located
The nucleus of every cell
contains DNA.
The DNA is organized in
genes and the genes are
located on
Chromosomes.
The best way to think
about it is like a library…. video press

6. 3.13 understand that the nucleus of a cell contains chromosomes on which genes are located
LIBRARY
Books
Chapters
Words
Letters
Nucleus
Chromosome
(23 pairs)
Gene
(makes one protein)
Group of 3 letters
DNA letters
(A, C, T, G)

7. 3.13 understand that the nucleus of a cell contains chromosomes on which genes are located

8. Genes Make a SPECIFIC Protein
3.14 understand that a gene is a section of a molecule of DNA and that a gene codes for a specific protein
1) Genes are written in DNA code.
2) The code can be translated into amino acids.
3) Amino Acids are linked together to make
proteins.
ONE Gene codes for ONE specific protein

9. Genes Make a SPECIFIC Protein
3.14 understand that a gene is a section of a molecule of DNA and that a gene codes for a specific protein
A three-base sequence codes for each amino acid.
base sequence amino acid

10. Genes Make a SPECIFIC Protein
3.14 understand that a gene is a section of a molecule of DNA and that a gene codes for a specific protein
Genes don’t actually make proteins – they just contain the instructions on how to make
them.
DNA stays in the nucleus but proteins are built in the cell’s cytoplasm.

11. 3.14 understand that a gene is a section of a molecule of DNA and that a gene codes for a specific protein
So Your Genes code for Your Proteins

12. WHAT IS DNA?
3.15 describe a DNA molecule as two strands coiled to form a double helix, the strands being linked by a series of paired bases: adenine (A) with
thymine (T), and cytosine (C) with guanine (G)
DNA is a very long molecule.
It is shaped like a twisted
ladder.
Two long strands make the
backbones and are connected
by rungs or links.

13. BASE PAIRS
3.15 describe a DNA molecule as two strands coiled to form a double helix, the strands being linked by a series of paired bases: adenine (A) with
thymine (T), and cytosine (C) with guanine (G)
The Strands are
connected by BASE
PAIRS
• Adenine (A)
• Thymine (T)
• Cytosine (C)
• Guanine (G)
The bases only match:
A-T
C-G

14. Genes come in Variations
3.16 understand that genes exist in alternative forms called alleles which give rise to differences in inherited characteristics
Sometimes more than one version of a gene occurs.
The different versions are called alleles
(i.e. we all have the gene for iris pigment (protein),
but there are different colours of iris pigment, same
gene but different alleles)

15. Alleles give rise to Variation
3.16 understand that genes exist in alternative forms called alleles which give rise to differences in inherited characteristics
over
view

16. Alleles give rise to Variation (2)
3.16 understand that genes exist in alternative forms called alleles which give rise to differences in inherited characteristics
Alleles give rise to a range of different inherited
characteristics in a population.
These can include in humans:
Eye Colour
Skin Colour
Hitch Hikers Thumb
Rolling of the tongue
Earlobe shape
Blood Type
Many many others………..

17. DEFINITIONS OF INHERITANCE TERMS
3.17 understand the meaning of the terms: dominant, recessive, homozygous, heterozygous, phenotype, genotype and co-dominance
Dominant:
A gene allele that ‘expresses’ over another allele in
homozygous and heterozyogus pairs. Shown in phenotype.
b
B
Recessive:
A gene allele that only ‘expresses’ when it is matched with
another recessive allele and never when matched with a
dominant allele. Homozygous Recessive. Shown in phenotype
b b

18. DEFINITIONS OF INHERITANCE TERMS
3.17 understand the meaning of the terms: dominant, recessive, homozygous, heterozygous, phenotype, genotype and co-dominance
Homozygous: having identical alleles at corresponding
chromosome Loci (Gene Location).
Heterozygous: having dissimilar alleles at
corresponding chromosomal Loci.
b B B B b b

19. DEFINITIONS OF INHERITANCE TERMS
3.17 understand the meaning of the terms: dominant, recessive, homozygous, heterozygous, phenotype, genotype and co-dominance

20. DEFINITIONS OF INHERITANCE TERMS
3.17 understand the meaning of the terms: dominant, recessive, homozygous, heterozygous, phenotype, genotype and co-dominance

21. DEFINITIONS OF INHERITANCE TERMS
3.17 understand the meaning of the terms: dominant, recessive, homozygous, heterozygous, phenotype, genotype and co-dominance
Phenotype: the set of observable
characteristics Geneotype
of an individual resulting
from the interaction of its genotype
with the environment
Genotype: The genetic makeup of a cell,
an organism, or an individual with
reference to a specific characteristic.
Environemnt
Phenotype

22. DEFINITIONS OF INHERITANCE TERMS
3.17 understand the meaning of the terms: dominant, recessive, homozygous, heterozygous, phenotype, genotype and co-dominance

23. 3.17 understand the meaning of the terms: dominant, recessive, homozygous, heterozygous, phenotype, genotype and co-dominance

24. DEFINITIONS OF INHERITANCE TERMS
3.17 understand the meaning of the terms: dominant, recessive, homozygous, heterozygous, phenotype, genotype and co-dominance
Codominance: A single gene has more than one dominant allele and both genes are
expressed.
The meaning of the prefix "co-" is "together". Cooperate = work together. Coexist =
exist together. Cohabitat = habitat together.
When writing alleles remember:
All alleles are CAPITAL letters
*I remember codominance in the form of an example like so:
red x ---> r d & h t s o t d

25. CODOMINANCE

26. Genetic Diagrams - Generations
3.18 describe patterns of monohybrid inheritance using a genetic diagram
Generations
There are the parents, then their offspring, and their offspring, etc. etc.
Each generation has a name.
The first plants or animals bred together are called the Parental generation, or P1 generation.
Their offspring are called the First Filial generation, or F1 generation.
Their offspring are called the Second Filial generation, or F2 generation.
And so on. And so on.

27. Genetic Diagrams – Punnett Squares
3.18 describe patterns of monohybrid inheritance using a genetic diagram
SOME SIMPLE EXAMPLES OF WHAT YOU CAN USE A
PUNNETT SQUARE FOR
SEED COLOUR FLOWER COLOUR GENDER
press

28. Genetic Diagrams – Punnett Squares
3.18 describe patterns of monohybrid inheritance using a genetic diagram
P1
P1
P1
Genotype of F2
press

29. Genetic Diagrams – Punnett Squares
3.18 describe patterns of monohybrid inheritance using a genetic diagram
How to diagram patterns in monohybrid inheritance:
1) Phenotype of Parents P1
2) Genotype of Parents
3) Gametes Produced
4) Genotype of F1 (you may need a Punnett square)
5) Phenotype of F1
6) Gametes from F1 produced
7) Genotype of F2 (you may need a Punnett square)
8) Phenotype of F2
9) What are the ratios of F2 Phenotype and Genotypes

30. Genetic Diagrams – Crossing
3.18 describe patterns of monohybrid inheritance using a genetic diagram
To cross two tall plants
1. The allele for tallness is H and is dominant to that for smallness, h.
2. If the two plants are heterozygous, they will have a genotype, which contains the alleles Hh.
3. Gametes of individuals contain half of the chromosomes. So only one of the alleles will be
present in each gamete cell.
So there will be 3
tall plants for every
1 small plant. Or to
put it another way,
there is a 75%
chance that each F1
(offspring) plant will
be tall.
press

31. TESTCROSS
3.18 describe patterns of monohybrid inheritance using a genetic diagram
Geneticists use the testcross to determine unknown Genotypes
A testcross can reveal an unknown genotype
1. Mate an individual of unknown genotype and a
homozygous-recessive individual
2. In a test cross you breed an organism showing the
dominant features with one showing the recessive
feature
3. Each of the two possible genotypes (homozygous
or heterozygous) gives a different phenotypic ratio
in the F1 generation

32. TESTCROSS
3.18 describe patterns of monohybrid inheritance using a genetic diagram

33. Pedigree Charts
3.19 understand how to interpret family pedigrees
A pedigree is a chart of the genetic history of family over several generations.
Constructing a Pedigree
• Female
• Male
Connecting Pedigree
Symbols
• Married
Couple
• Siblings
• Fraternal
twins
• Identical
twins
• Not Affected
• Affected
• Deceased

34. Example (Dominant or Recessive)
3.19 understand how to interpret family pedigrees
Is the Affected allele Dominant or Recessive?
Affected Unaffected
aa AA
RECESSIVE
Aa Aa Aa
aa aa
aa
Aa Aa
aa aa
aa

35. Example (Dominant or Recessive)
3.19 understand how to interpret family pedigrees
Is the Affected allele Dominant or Recessive?
Affected Unaffected
Aa aa
Aa Aa
DOMINANT
aa aa
Aa Aa Aa
AA
AA aa
Aa

36. Interpreting a Pedigree Chart (hard)
3.19 understand how to interpret family pedigrees
Determine if the pedigree chart shows:
• An autosomal disease
-The disease Allele is not on Sex
Chromosome (X Y)
-The disease Allele can be dominant or
recessive
• X-linked disease
-The disease Allele is found on X Sex
Chromosome
-( X = Normal Allele, Xr = Disease Recessive
Allele)
press
If it is a 50/50 ratio between men and
women. The disorder is autosomal.
Most of the males in the pedigree are
affected. The disorder is X-linked
press

37. Interpreting a Pedigree Chart (additional)
3.19 understand how to interpret family pedigrees
Sex Linked diseases can include:
• Hemophilia (Xr) - Recessive
• Colour blindness (Xr) - Recessive The phenotype of a Carrier
is “NOT DISEASED”

38. Example (Dominant or Recessive)
3.19 understand how to interpret family pedigrees
Example of Pedigree Charts
• Is the affected trait Autosomal or X-linked?
AUTOSOMAL
If it is a 50/50 ratio between men and
women. The disorder is autosomal.

39. Example (Dominant or Recessive)
3.19 understand how to interpret family pedigrees
Summary
• Pedigrees are family trees that explain your genetic
history.
• Pedigrees are used to find out the probability of a
child having a disorder in a particular family.
• To begin to interpret a pedigree, determine if the
disease or condition is autosomal or X-linked and
dominant or recessive.

40. Monohybrid Cross Probability
3.20 predict probabilities of outcomes from monohybrid crosses
GIVE THE GENOTYPE RATIO:
GIVE THE GENOTYPE RATIO:
GIVE THE PHENOTYPE RATIO:

41. Male or Female
3.21 understand that the sex of a person is controlled by one pair of chromosomes, XX in a female and XY in a male

42. Male or Female
3.21 understand that the sex of a person is controlled by one pair of chromosomes, XX in a female and XY in a male
XX = Female
XY = Male

43. Determine the Sex (diagram it)
3.22 describe the determination of the sex of offspring at fertilisation, using a genetic diagram

44. Diploid Cell Division
3.23 understand that division of a diploid cell by mitosis produces two cells which contain identical sets of chromosomes

45. What are homologous chromosomes?
3.23 understand that division of a diploid cell by mitosis produces two cells which contain identical sets of chromosomes
Different organisms have different numbers of chromosomes. Humans
have 46 chromosomes. This is the diploid number of humans.
Chromosomes can be grouped in pairs called homologous
chromosomes. In each pair, one chromosome has been inherited
from the mother and the other inherited from the father.
homologous pair
chromosome from
mother
chromosome from
father

46. What are homologous chromosomes?
3.23 understand that division of a diploid cell by mitosis produces two cells which contain identical sets of chromosomes
2n
Body cells are: 2n - Diploid
Sex Cells are: n - Haploid
2n
2n

47. What is Mitosis good for?
3.24 understand that mitosis occurs during growth, repair, cloning and asexual reproduction
MITOSIS
GROWTH
New cell growth
Nerve cells
(tissue)
Muscle cells
(tissue)
Repair
Scar tissue
Replace old cells
RBC
Skin
Cloning Dolly the sheep
Asexual
Reproduction
Budding
Bacteria & Yeast
Cuttings, Bulbs,
Tubers, Runners
Willow
Tulips
Potatoes
Strawberries

48. Meiosis Makes Gametes
3.25 understand that division of a cell by meiosis produces four cells, each with half the number of chromosomes, and that this results in the
formation of genetically different haploid gametes

49. Meiosis Makes Gametes
3.25 understand that division of a cell by meiosis produces four cells, each with half the number of chromosomes, and that this results in the formation of
genetically different haploid gametes
3.27 know that in human cells the diploid number of chromosomes is 46 and the haploid number is 23
MITOSIS MEIOSIS
1) Produces 2 daughter cells
2) Daughter cells are diploid
(have 23 pairs of chromosomes)
3) Daughter cells are genetically
identical to each other.
3) Gametes are different to
each other
4) Gametes are different to
the parent cell (crossing over of
genetic material)
5) Two stage process
6)Happens in Reproductive
organs only
4) Daughter cells are genetically
identical to the parent cell (no
genetic crossing over)
5) One stage process
6) Happens everywhere in the
body
1) Produces 4 gamete cells
2) Daughter cells are haploid
(Only have 23 chromosomes)

50. Random Fertilization and Variation
3.26 understand that random fertilisation produces genetic variation of offspring

51. Key Word basic Summary
This topic, more than any other, confuses people. Remember these!
DNA: A genetic code
Gene: One instruction in the code telling a cell how to make a
specific protein
Allele: A different version of a gene
Chromosome: Coiled up DNA
Haploid number: the number of different chromosomes in a cell (23)
Diploid number: the total number of chromosomes in a cell (46)
Cell Division:
There are two types of cell division;
- Mitosis – used for growth, repair & asexual reproduction
- Meiosis – used to produce gametes for sexual reproduction

52. Nature Vs Nurture
3.28 understand that variation within a species can be genetic, environmental, or a combination of both
Variation

53. Mutations
(not all x-men get superpowers)
3.29 understand that mutation is a rare, random change in genetic material that can be inherited
3.31 understand that many mutations are harmful but some are neutral and a few are beneficial
Mutation - a rare, random change in the genetic code of a gene.
The mutated gene will produce a slightly different protein to
the original non-mutant gene. The new protein might;
A) Work just as well as it did before (neutral mutation)
B) Work better than before (beneficial mutation)
C) Work worse / not at all (harmful mutation)
Beneficial mutations give a selective advantage to the individual.
Individuals with this kind of mutated allele are more likely to survive,
reproduce and pass their alleles on. This is the basis of:
Natural Selection

54. Evolution by Natural Selection
3.30 describe the process of evolution by means of natural selection
Evolution is the process by which the range of
organisms on Earth change
New species arise through a process known as
NATURAL SELECTION
1) Living organisms produce more offspring than are needed
to replace them, not all of these off-spring grow up and
breed themselves. These offspring have different alleles.
2) Those organisms best suited to their local environment
survive best and breed, passing on their genetic
(genes/DNA) information to the next generation
3) In this way the different forms will become more and
more different until eventually they are a new species

55. WHAT IS THE SELECTION METHOD
3.30 describe the process of evolution by means of natural selection
HOW TO BE SUCCESSFUL IN PASSING ON YOUR
GENES (A HOW TO 5 STEP GUIDE):
1) BE ATTRACTIVE (physical and social traits can make you more
successful with the opposite sex)
2) REPRODUCE OFTEN (The more offspring you make the better)
3) DON’T WASTE YOUR RESOURCES (Invest only the minimal
amount of resources in offspring to see them through to
reproduction)
4) HAVE A ‘DEEP’ GENE POOL (The more variable your offspring
the better chance of some of them surviving unexpected
catastrophes. A little bit of mutation/lots of alleles is not a bad
thing)
5) STAY ALIVE!! (Live long enough to reproduce………....then die.)

56. DARWIN SAID IT BEST
3.30 describe the process of evolution by means of natural selection
Darwin came up with this theory
1) Darwin’s 1st Observation: Not all
individuals survive
2) Darwin’s 2nd Observation: There is
variation in a species
3) Darwin’s Conclusion: The better
adapted individuals survive (the
“fittest”) and reproduce, passing their
alleles onto the next generation.
Over time this process leads to evolution.
www.darwinawards.com/

57. THE SUPERBUGS
3.32 understand that resistance to antibiotics can increase in bacterial populations, and appreciate how such an increase can lead to infections
being difficult to control
1) Bacteria reproduce very frequently so mutations (different alleles) are common.
2) These mutations can mean that they are no longer affected/controlled by a certain
antibiotic
3) Surviving generations carry the mutation (allele)making it easier for them to survive.
4) If bacteria evolve over many generations to be resistant to drugs we are treating
them with then they are difficult to control
5) Sometimes they can be controlled using a different antibiotic
6) These bacteria in turn become resistant to new antibiotics due to the high rate or
reproduction and random mutations
7) Currently some are becoming resistant to all current know antibiotics.
Methicillin-resistant Staphylococcus aureus (MRSA or golden staph), vancomycin-resistant
Enterococcus (VRE) and multi-drug-resistant Mycobacterium tuberculosis (MDR-TB)
✔

58. The Makings of a Mutant (TA)
3.33 understand that the incidence of mutations can be increased by exposure to ionising radiation (for example gamma rays, X-rays and
ultraviolet rays) and some chemical mutagens (for example chemicals in tobacco).(TA)
Mutations are: a) inherited b) happen on their own
(although this is rare).
The frequency that mutation occurs naturally can be
increased by exposure to radiation
• gamma rays
• X-rays
• ultraviolet rays
And
Chemical mutagens
• chemicals in tobacco..Not Nicotine!)