Download Biological Approach

Biological Approach
L.O. To discuss the main themes
of the biological approach
To revise(?) information about
genes (genotypes and
phenotypes)
Brace yourselves – I am going to
talk fast at you for the lesson!
Homework
• Complete P5 + 6 in your workbooks.
BRAIN FACTS
• weighs 1300 1400 g
• made up of about
100 billion neurons
• makes us who we
are
•“the most complex living structure on the universe”
Society for Neuroscience
How many brain cells do you think you
have?
A:
1,000
B:
1,000,000
C:
1,000,000,000
D:
1,000,000,000,000
If you were to join all your brain cells together,
how far do you think they would stretch?
A:From here to Durham
B: From here to London
C: From here to the moon
D:From here to Australia
Which of the following buildings would be
able to house a computer with the same
capacity of your brain?
A:The Empire State Building
B: Your School
C: The Metro Centre
D:The Houses of Parliament
How much information do you think you
are capable of storing in your brain?
A:
An Encyclopaedia
B:A Computer
C:The school library
D:
The world’s telephone exchange
What percentage of you body’s oxygen
does your brain consume?
A:
10%
B:
25%
C:
50%
D:
75%
NATURE NURTURE DEBATE
• How much of ‘you’ do you think is due to
what you have inherited from your
parents or from your life experiences.
• NATURE is what we are born with
• NURTURE is what we experience
Neuroanatomy
Biochemistry
3 features of the approach
Genes
1. GENETIC INHERITENCE
 characteristics inherited via genes
2. BIOCHEMISTRY
 Chemical activity (neurotransmitters and hormones)
3. BRAIN STRUCTURE
 What different parts of the brain do
GENETIC INHERITENCE
Does having a Y
chromosome
make someone a
man?
Genotype
bb
Gb
BLUE
GREEN
The genes, or combination
of chromosomes someone
has for a particular
characteristic. (XX, XY)
Phenotype
The characteristic that is
displayed (physical,
behavioural or
psychological)
what exactly do we inherit? Can we change our
physical characteristics or are they fixed?
BIOCHEMISTRY
Neuronal cell
bodies
Axons
Synapses occur
at the junctions
psychlotron.org.uk
Source: science photo library
What are neurotransmitters and what do they do?
BRAIN STRUCTURE
If we damage our brains how does that affect
our behaviour? What if someone is born with
brain defects?
• Genes:
• determine the structure of the
brain
• determine the levels of
hormones and
neurotransmitters
• Tell the body how to function
METHODOLOGY WE WILL STUDY
• Scientific approach
– Experiments
– Brain scans
– Animal experiments
• Non-experimental
– Twin and adoption studies
BRAIN LATERALISATION
• What do the
two sides of
our brains
control?
• Are there
differences
between male
and female
brains?
• As you were growing up, how did you know you were
a girl or a boy? Was it because you had a vagina or a
penis? Or was it something more than your
physiology?

Some people feel that their minds and bodies don't quite
match up. This feeling is commonly known as transsexualism - a type of gender identity disorder.
ANIMAL EXPERIMENTS
• How ethical is it to use
animals in research?
• Are animals the same as
humans?
2 x STUDIES IN DETAIL
• MONEY (1975) case study of David
Reimer
• GOTTESMAN & SHIELDS (1966)
schizophrenia twin study
PRACTICAL
• Experiment
• Mann- Whitney U
• Test the difference between gender
KEY ISSUE
• How ethical are
transgender operations?
Use these websites to find the definitions and learn
more about the role of synapses and neurons
• http://outreach.mcb.harvard.edu/animations/synaptic.s
wf
• http://faculty.washington.edu/chudler/neurok.html
• http://learn.genetics.utah.edu/content/addiction/rewar
d/madneuron.html
Revision of genes
Note: You do not need to take any
notes. This ppt will be on the system
if you need to go back and revise. You
will only need to be able to do the
examples I ask of you.
What is DNA?
Chromosomes and their genes are made of a molecule
called DNA.
DNA stands for
deoxyribonucleic
acid.
Each chromosome
is a very long molecule
of tightly coiled DNA.
DNA molecules carry the code that controls what cells are made of and what
they do.
Which part of a DNA molecule holds this information?
The structure of DNA
What are proteins?
Proteins are made of long chains of amino acids. There are 20 different types of
amino acid from which to make proteins.
protein
molecule 1
amino acids
What happens if the amino acids are in a different order?
protein
molecule 2
Different combinations of amino acids make different proteins.
Phenotype and genotype
The overall ‘characteristics’ of an organism depends on two things:
1. its genes (inherited characteristics)
2. the effects of the environment in which it lives.
All the observable characteristics of an organism are called its phenotype.
The full set of genes of an organism is called its genotype.
An organism’s phenotype therefore depends on its genotype plus environmental
effects.
phenotype = genotype + environmental effects
Observing variation in humans
As well as environmental factors such as climate and diet, humans are affected by
education, culture and lifestyle.
Because these factors change our phenotype, the effects of many environmental
factors can be clearly seen.
Scientists often use identical twins to study the effects of
environmental factors. Although the twins are genetically
identical, each one will have been shaped differently by their
environment and experiences.
For example, a bad diet may cause one twin to be larger and less
healthy than the other twin.
Genetic causes of variation
Sexual reproduction is the most important cause of genetic variation because it mixes
up genetic material.
How does it do this?
 During meiosis, homologous chromosomes
exchange genetic material. They then line up and
separate in different ways, producing a large
variety of different gametes.
 At fertilization, any male gamete can combine with
any female gamete.
All these events occur randomly and create new combinations of
genetic material.
Different versions of genes
Chromosomes in a homologous pair contain the same type of genes that code for the
same characteristics, such as eye colour.
Each chromosome in the pair, however, may
have a different version of the gene.
allele for
brown
eyes
For example, the version of
a gene on one chromosome
may code for brown eyes,
whereas the version of the gene on the other
chromosome may code for blue eyes.
Each different version of a gene is called an allele.
allele for
blue
eyes
Homozygous alleles
If the alleles for a characteristic in a homologous pair are the same, the organism is said
to be homozygous for that characteristic.
What colour eyes will these homozygous pairs of alleles produce?
allele for
brown eyes
allele for
brown eyes
allele for
blue eyes
allele for
blue eyes
Heterozygous alleles
If the alleles for a characteristic in a homologous pair are different, the organism is said
to be heterozygous for that characteristic.
What colour eyes will this heterozygous pair of alleles produce?
?
allele for
brown eyes
allele for
blue eyes
The characteristic expressed by
heterozygous alleles will depend on which
allele is dominant and which allele is
recessive.
Dominant or recessive?
The phenotype for a particular characteristic depends on which allele is dominant and
which allele is recessive.
 Dominant alleles are always expressed in a cell’s phenotype. Only one
copy of the dominant allele needs to be inherited in order for it to be
expressed. Dominant alleles (e.g. brown eyes) are represented by an
upper case letter (e.g. ‘B’).
 Recessive alleles are only expressed in a cell’s phenotype if two copies
of it are present. If only one copy is present, its effect is ‘masked’ by the
dominant allele. Recessive alleles (e.g. blue eyes) are represented by a
lower case letter (e.g. ‘b’).
What eye colour?
The allele for brown eyes is dominant over the allele for blue eyes.
So, what colour will the eyes be of an individual who is heterozygous for eye
colour?
allele for
brown eyes
allele for
blue eyes
The individual will have brown eyes,
because the allele for brown eyes masks
the allele for blue eyes.
Heterozygous cross
What are sex chromosomes?
Humans cells contain one pair of sex chromosomes, which control gender.
Y chromosome
 Males have one X and
one Y chromosome (XY).
 Females have two X chromosomes
(XX).
Y chromosomes are very small and contain 78
genes, whereas
X chromosomes are larger and contain a 900–
1,200 genes.
X chromosome
Because females can only produce X gametes, it is the sperm that determine the sex of
the offspring at fertilization.
Boy or girl?
A boy or a girl?
In the first 6-8 weeks
(Male)
(Female)
All foetuses have the same undeveloped sex organs. The original
system can develop into both male or female sex organs. It is
the presence or absence of a single gene (SRY gene) which will
dictate the future development of the foetus as a male or a
female.
Male development
XY
Male development
SRY gene produces a protein :
Testis Determining Factor (TDF)
TDF influences the development
of the gonads, they become testis
The testis produce testosterone
Testosterone triggers the
development of external male
organs i.e. penis
Female development
• The absence of male hormone will result in
the development of the Mullerian system into
female sex organs
Puberty
After around 10 years, the hypothalamus
releases a hormone which affects the anterior
pituitary gland and this causes the gonads to
become active. They control the development of
secondary sexual characteristics.
What are inherited diseases?
Inherited diseases are diseases caused by faulty genetic material that is passed on to
future generations. They are sometimes called genetic disorders.
Many inherited diseases are caused by mutations in DNA,
resulting in faulty alleles that are not properly expressed.
Mutations can be spontaneous or caused by exposure to
mutagens such as radiation and certain chemicals.
There are over 4,000 known inherited diseases, although
the specific alleles involved are only known for 25% of them.
What is Huntington’s disease?
Huntington’s disease, sometimes called Huntington’s chorea, is a rare and fatal
inherited disease of the central nervous system.
Huntington’s disease is caused by a single dominant
allele, which means that heterozygous individuals will
develop the disease.
The disease causes damage to brain cells, leading to a
gradual loss of co-ordination, decline in mental ability
and changes in personality.
Around 4,800 people in the UK have Huntington’s disease.
The symptoms of Huntington’s disease
Symptoms of Huntington’s disease usually begin to develop between the ages of 30 and
50, although they can appear earlier in rare occasions.
Early symptoms include:
 twitching, clumsiness and stumbling
 lack of concentration and memory loss
 depression and mood changes
Huntington’s disease is incurable, but medication can help to reduce the
symptoms. However, as the disease progresses, the person’s co-ordination and
movement becomes worse, and their mental abilities decline further.
How is Huntington’s disease diagnosed?
Huntington’s disease is usually diagnosed from the physical symptoms of the patient
and a family history of the disease.
The diagnosis is confirmed by a blood test that detects the Huntington’s disease
allele. This test can also be used in people who have yet to show symptoms but who
have a family history of the disease.
Why might this be useful for someone planning to have children?
People with the Huntington’s disease allele generally develop the disease later in life,
so they may unknowingly pass the allele on to their children before realizing that they
have the disease.
The inheritance of Huntington’s
disease
Patterns of inheritance: Huntington’s
What is Down’s syndrome?
Down’s syndrome is a genetic disorder that occurs when a person inherits an extra
copy of chromosome 21.
People with Down’s syndrome often have characteristic physical features, learning
disabilities and have a higher risk of certain medical conditions.
The risk of having a child with Down’s
syndrome increases with maternal age,
especially over the age of 40.
In the UK, Down's syndrome affects about
one in every 1,000 children born each year.
How is Down’s syndrome diagnosed?
During pregnancy, ultrasound and amniotic cell tests can be used to estimate the
probability that a baby has Down’s syndrome.
After the baby is born, the diagnosis can be
confirmed by taking a blood or tissue sample,
and observing the shape and number of
chromosomes under a microscope.
How would a scientist recognize Down's
syndrome by looking at chromosome number?
1
2
3
4
5
8
9
10
14
15
6
7
11
12
13
16
17
18
19
20
21
X
22
Down’s syndrome and trisomy 21
• Maybe linked to certain mental
disorders and behaviours?
• TBC…………………………