A useful resource for Junior Certificate Science (Biology)

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Junior Certificate Science BiologyJunior Certificate Science Biology
Inheritance and SelectionInheritance and Selection
Theresa Lowry-LehnenTheresa Lowry-Lehnen
RGN, BSc (Hon’s) Specialist Clinical Practitioner (Nursing), Dip Counselling, Dip AdvRGN, BSc (Hon’s) Specialist Clinical Practitioner (Nursing), Dip Counselling, Dip Adv
Psychotherapy, BSc (Hon’s) Clinical Science, PGCE (QTS), H. Dip. Ed, MEd,Psychotherapy, BSc (Hon’s) Clinical Science, PGCE (QTS), H. Dip. Ed, MEd,
Emotional Intelligence MHS AccreditedEmotional Intelligence MHS Accredited

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VariationVariation
“Variation” is the name given to differences between
individuals of the SAME species.
Variation is due to GENETIC or ENVIRONMENTAL causes.
For example, consider identical twins:
1) Ways in which Tom and
James are the same (caused
by genes):
2) Ways in which Tom and
James are different (caused
by environment):

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Where is this information stored?Where is this information stored?
Section of a chromosome:
Genes for
eye colour
Genes for
hair colour
Genes for
blood group:
Different species have different numbers
of chromosomes. Humans have 46 (23
pairs) in every cell.

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Sexual ReproductionSexual Reproduction
The human egg
and sperm cell
(“GAMETES”)
contain 23
chromosomes
each.
When fertilisation happens the
gametes fuse together to make
a single cell called a ZYGOTE.
The zygote has 46
chromosomes (23 pairs).

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Sexual vs. Asexual reproductionSexual 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”)

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MitosisMitosis
Each daughter cell has
the same number of
chromosomes and genetic
information as the parent.

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MeiosisMeiosis
Each daughter cell has half
the number of chromosomes
of the parent.

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Mitosis vs. MeiosisMitosis 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
Meiosis:
1. Used to produce gametes for
sexual reproduction
2. Each daughter cell has half the
number of chromosomes of the
parent

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FertilityFertility
The events that happen in a female body during the menstrual
cycle are triggered by hormones (chemical messengers).
Artificial hormones can be used to:
In normal circumstances natural
hormones are responsible for releasing
the egg and for thickening the lining of
the womb. These hormones are
produced by the pituitary gland in the
brain and in the ovaries.
1) Stimulate the release of eggs
(fertility treatment)
2) Inhibit the release of eggs
(contraceptive pills)

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FertilityFertility
3 hormones are involved in the menstrual cycle: oestrogen, LH and FSH.
Here’s how:
Step 3: LH
stimulates the
release of the
mature egg in
the middle of
the menstrual
cycle
Artificial fertility:
1) To INCREASE fertility FSH is given to stimulate maturation of eggs.
2) To DECREASE fertility oestrogen is given (“The Pill”) to inhibit FSH
production stopping eggs from maturing.
Step 1: FSH
produced by the
pituitary gland
causes both an egg
to mature and the
ovaries to start
producing oestrogen
Step 2: The rising levels of
oestrogen cause the pituitary
gland to stop producing FSH
and produce LH instead

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Key wordsKey words
Gamete
Zygote
Allele
Dominant
Recessive
Homozygous
Heterozygous
•This allele determines the development of a
characteristic
•This is formed when an egg is fertilised by a sperm
•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
•An egg or a sperm are called this
•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

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Genes, Chromosomes and DNAGenes, Chromosomes and DNA

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Some facts:
- Made up of paired bases
- Contain instructions on what a cell does, how the organism
should work etc
- The instructions are in the form of a code
- The code is made up from the four bases that hold the
strands together
- The bases represent the order in which amino acids are
assembled to make proteins
- Each group of 3 bases represents one amino acid
- There are only about 20 amino acids
How genes workHow genes work

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Boy or Girl?Boy or Girl?
X Y X
XX XY
Girl Boy
“Allele”

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Father
Mother
Son
Daughter
Boy or Girl?Boy or Girl?

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Eye colourEye 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:
bbBB Bb
Homozygous
brown-eyed
parent
Heterozygous
brown-eyed
parent
Blue-eyed parent
What would the offspring have?

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Eye colourEye colour
Example 1: A homozygous
brown-eyed parent and a
blue-eyed parent:
Example 2: 2 heterozygous
brown-eyed parents
BB bbX Bb BbXParents:
Gametes:
Offspring: Bb Bb BbBb BB Bb bbbB
B B bb B bB b
(FOIL)
All offspring have brown eyes 25% chance of blue eyes

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Eye colourEye colour
Example 3: A heterozygous brown-eyed
father and a blue-eyed mother:
Bb
Bb Bb bbbb
bb
b bB b
Equal (50%)
chance of
being either
brown eyed or
blue eyed.

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B b
b
b
Another methodAnother method
Example 3: A heterozygous brown-eyed
father and a blue-eyed mother:
B b
b Bb bb
b Bb bb
Father
Mother

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Example questionsExample 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).

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Inherited diseasesInherited diseases
1) Cystic fibrosis (1 in 2000)– a disease that causes thick and sticky mucus
to coat the lungs, gut and pancreas. It’s caused by recessive alleles:
2) Huntingdon's disease (1 in 20,000)– a disease of the nervous system
that causes shaking and eventually dementia. It’s caused by a dominant
allele:
3) Sickle cell anaemia – a disease that alters the shape of red blood cells,
thereby reducing their oxygen capacity, causing weakness and anaemia.
It’s caused by recessive alleles:
Ff FfX
Cc ccX
Ss SsX

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MutationsMutations
Mutations are changes in the structure of the DNA molecule. They can be
passed on to daughter cells through cell division. They will result in the
wrong proteins being produced.
Mutations can be caused by:
- Ionising radiation (UV, X-rays etc)
- Radioactive substances
- Certain chemicals
Effects:
- Mostly harmful
- Causes death or abnormality in reproductive cells
- Causes cancer in body cells
- Some CAN be neutral or even beneficial (e.g. the peppered moth)

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Modern GeneticsModern Genetics
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:

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Modern GeneticsModern 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
determiners”

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ClonesClones
Plants can reproduce ASEXUALLY. The offspring are
genetically ________ to the parent plant and are called
_________. 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

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CloningCloning
1) Cloning plants:
2) Cloning sheep:

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Selective breedingSelective 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.
Friesian
Jersey
Hereford

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Selective breeding vs. CloningSelective breeding vs. Cloning
Advantages Disadvantages
Cloning
Selective
breeding

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Selective breeding vs. CloningSelective breeding vs. Cloning
Advantages Disadvantages
Cloning
1) Allows large
numbers of
organisms with good
characteristics to
be produced
2) Very efficient
1) Causes reduced
numbers of alleles
2) Loss of variation
could harm survival
chances if the
environment changes
Selective
breeding
1) Produced organisms
with favoured
characteristics
2) Very efficient and
economically viable
1) Causes reduced
numbers of alleles
2) Loss of variation
could harm survival
chances if the
environment changes

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Genetic ModificationGenetic Modification
Possible uses of genetic modification of organisms:
-Improving crop yield
-Improving resistance to pesticides
-Extend shelf-life
-Manufacture a certain chemical (e.g. insulin)
-Convenience

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Genetic engineeringGenetic engineering
Insulin is a hormone produced by the pancreas to help control
blood sugar levels. Diabetics can’t produce enough insulin and
often need to inject it.
Insulin can be made by genetic engineering:

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Genetic engineering - InsulinGenetic engineering - Insulin
Step 1: Using RESTRICTION
ENZYMES “cut out” the part of
the human chromosome that is
responsible for producing insulin.
Step 2: Using another restriction
enzyme cut open a ring of bacterial
DNA (a “plasmid”). Other enzymes
are then used to insert the piece of
human DNA into the plasmid.
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
instruction to produce insulin. Commercial
quantities of insulin can then be produced.

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EvolutionEvolution
Charles Darwin (1809-1882)

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EvolutionEvolution
Evolution is the slow, continual change of
organisms over a very long time. All
living things on the Earth have
developed from the first simple life
forms that arrived 3,000,000,000 years
ago.
One of the effects of evolution is that species will become
better adapted to their environment. If these species
don’t adapt they may become extinct due to being unable to
deal with any of these factors…
1) Increased competition
2) Changes in the environment
3) New diseases
4) New predators

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EvolutionEvolution
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.

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Natural SelectionNatural 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”

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A smaller example…A smaller example…
Consider the four steps of natural selection in the example of
some bacteria that has become resistant to penicillin:
1) Variation – some strains of bacteria
are resistant and some aren’t.
2) Competition – The non-resistant
bacteria are killed by the penicillin.
3) Survival of the fittest – the
resistant bacteria survive.
4) Passing on of genes – the resistant
bacteria reproduce and pass on
their adaptations to their
offspring.
Bacteria
Penicillin