Transcript Genes and the environment File

Topic 3.4
14 Explain how a phenotype is the result of an
interaction between genotype and the
environment (e.g. animal hair colour, human
height, monoamine oxidase A (MAOA) and
cancers), but the data on the relative contributions
of genes and environment is often difficult to
interpret.
 15 Explain how some phenotypes are affected by
alleles at many loci (polygenic inheritance) as well
as the environment (e.g. height) and how this can
give rise to phenotypes that show continuous
variation.
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 What
is a phenotype?
• The characteristics of an organism.
• What determines the phenotype?
 Genotype and environment
 What
is meant by the term gene?
• A length of DNA which codes for a certain
protein
• The same gene is always found at the
same location on the same chromosome
(same locus) and on its homologous pair
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Read page 134
What is discontinuous
variation?
• distinct groups:
Give examples
• blood type
• Sex (gender),
• tongue rolling,
• attached ear lobes
Cause?
• one gene at a
single locus
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What is continuous variation:
• Many possibilities within a
range, no distinct groups.
• Bell-shaped curve: normal
distribution
Examples?
• height in humans,
• length of feet,
• weight
Cause?
• several genes at different
loci and environmental
influences.
 Read
page 135-136 and do the following:
• Define: locus, allele, polygenic, susceptibility,
multi-factorial
• Complete questions 3.18 and 3.19.
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Locus:
• specific location of a gene on a chromosome.
Allele:
• one form of a gene
Polygenic inheritance:
• An inheritable characteristic that is controlled by the
interaction of several alleles at many loci (seveal genes).
Susceptibility to a condition:
 Inheriting a gene making you more likely to get to a
certain condition- environmental factors will increase or
decrease this chanceMulti-factorial:
• Conditions where several genes and environmental
factors are interacting.
 Human
height
 Hair colour
 MAOA (monoamine oxidase A)
 Cancer
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It has changed over the last two centuries. People in the UK are
on average 8cm taller than in 1850.
What is the evidence that the environment plays a role?
• Improved nutrition
 Increased protein in diet leading to more muscle and bone growth
leading to increased average height.
 Increased Calcium in diet leading to more bone growth
• Improved health (less infectious diseases, cleaner water,
increased use of vaccinations, antibiotics…etc) leading to
more energy for growth.
• More energy available for growth
 End of child labour Better insulation-
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It has changed over the last two centuries. People in the UK are
on average 8cm taller than in 1850.
What evidence is there from the graph below to suggest that
height is affected by genotype as well as the environment.
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• Maximum height potential
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It has changed over the last two centuries. People in the UK are
on average 8cm taller than in 1850.
How could the gene pool (collection of all alleles in a
population) change? Note: in this time period there can be no
significant change due to evolution.
• Migration- emigration or immigration from or to countries
where more people are on average taller/shorter
 Activity
3.16 Many Genes can affect a single
characteristic
 Activity 3.17 Are we still getting taller?
 Collect data for homework
 Analyse data using laptops
 Describe the shape of the graph. What does
this show about the type of variation? If the
shape is not what you expected explain.
 What is meant by standard deviation? How
can calculating it for a set of data help us?
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Define these words
Melanin:
• A dark pigment (light absorbing chemical)
Melanocytes:
• Cells that make melanin. These cells found in the skin and
in hair follicles.
Melanocyte stimulating hormone (MSH)
• regulates the production of melanin
MSH receptors:
• MSH bind with them to activate melanin producing genes
in the melanocytes
Melanosomes:
• Organelles, melanocytes place melanin into them. They
transfer the melanin to nearby skin or hair follicle cells
 Genetic
component?
• Different alleles for different number of
MSH receptors- more receptors results
in darker colour
 Environmental factors?
• UV light increases the amount of MSH
and number of MSH receptors in skin
• UV light destroys the melanin in hair
Arctic Foxes- Read pages 138 and 139
 What happens in summer?
• In summer white fur grows under the brown fur
because fewer MSH receptors are produced
• Therefore, MSH has less effect
• Less melanin in hair results in (almost)white fur.
 What happens in autumn?
• In autumn the dark fur is shed and the white fur can
be seen
 Suggest what the environmental factor could be.
 What is the role of genes in this?
 Answer questions 3.21, 3.22
 Describe
the fur of a himalayan rabbit.
 Write down the word equation for the
reaction producing melanin.
 What is the environmental factor?
 What happens when it is at normal body
temperature? Below normal body
temperature?
 What is the role of genes?
 Answer Q3.24
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Monoamine oxidase A: What is it?
• This enzyme speeds up the breakdown of
neurotransmitters and has been linked to dealing with
stress
What is the link between low levels of this enzyme and
aggressive behaviour in humans?
• Studies have shown no/little link between low levels
and aggressive behaviour
• However, low levels combined with maltreatment of
children has been linked to aggressive
behaviour/violent crime
What is the environmental factor?
What it the role of the genotype?
 Read
page 139-141
 What is a tumour?
• A mass undifferentiated of cells. The cells
multiply faster than they die.
 What causes a tumour to form?
• Damage to DNA. Carcinogens (e.g. in
cigarette smoke) or ionising radiation, like
UV rays/X-Rays, can increase the chance of
DNA getting damaged (mutating)
 Tumours
more likely to develop in the
lungs, bowel, skin, bone marrow: why?
• In these areas there is more mitosis and more
chance of mutation
 What
are the steps of the cell cycle? How
is the cell cycle controlled?
• G1, S, G2, Mitosis (pages 114-117)
• The cell cycle is controlled by regulatory
proteins.
• When these proteins are present they either
stimulate or inhibit the cell cycle from
progressing.
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What are oncogenes?
• They are genes which code for these regulatory proteinsones which stimulate the progression from one stage to
the next of the cell cycle.
What happens when there are mutations in oncogenes?
• Cell cycle occurs uncontrolled and without stopping.
What are tumour suppressor genes?
• They code for proteins which stop the cell from moving
from one stage to the next in the cell cycle.
What happens when there are mutations in tumour
suppressor genes?
• The cell cycle continues (cell moves from one stage to the
next) without stopping.
 Give
an example of a gene which a
person can inherit which makes them
susceptible (predisposes) them to
cancer?
 Describe the function of the protein
which this gene codes for.
 How
can you reduce your risk of getting
cancer?
• don’t smoke
• avoid excessive exposure to UV light, X-rays,
other ionising radiation
• eat a diet high in antioxidants
1.
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4.
5.
Describe the relationship between UV light and the
production of melanin in human skin cells. (3)
Explain how differential gene expression could result in the
specialisation of cells.
(3)
Describe the distribution of colour in a Siamese cat. (2)
Suggest an explanation for the distribution of dark-coloured
fur in a Siamese cat.
(3)
Define the following terms1. Polygenic
(1)
2. Allele
(1)
3. Multifactorial (1)
4. Phenotype
(2)
1. UV light increases the amount of MSH/ MSH receptors;
In melanocytes;
Causing them to produce more melanin
(3)
2.
3. Black tips; white body
(2)
4.
idea that ears etc., have a lower temperature (than the
rest of body);
(therefore) enzyme is {active / not denatured / eq};
pigment produced / eq;
no pigment produced in other parts because enzyme is
{inactive / denatured} / eq; max 3
5. 1. When a number of genes code for one characteristic
2. different form of a gene
3. Conditions where several genes and the environment are
involved in its development
4. characteristics of an organism; can be affected by the
genotype and/or the environment
(5)