Transcript You + Your Genes

You + Your Genes
B1 Revision Notes
Individual Characteristics
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Features determined either owing to
environment or inheritance. Examples?
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Variation amongst individuals
Organisms made of cells.
Cells controlled by a nucleus containing
chromosomes.
Each chromosome is made of thousands of
genes which control how you develop.
Genes tell the cell how to make proteins (50,000
types in human body).
Chromosomes
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Put in correct order, largest 1st
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Chromosome, gene, cell, nucleus
Each body cell contains 46 (23 pairs)
chromosomes. 23 from each parent.
 Only sex cells (gametes) contain only 23
chromosomes.
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Genes and
Alleles
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Chromosomes pair up and genes for the same
feature align next to each other.
Different versions of the same gene are called
alleles, e.g. eye colour (brown and blue alleles,
but gene for the same feature).
One allele is always dominant and means this
feature shows up. The other allele is recessive.
Genetic Crosses
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Mum has 2 alleles,
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A and a for hair colour.
Dad has the same ones.
 A is brown hair
 a is blond hair.
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Both parents have brown hair.
What is chance of offspring having blond?
X and Y
XX is female.
 XY is male.
 Y dominates.
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50:50 chance of either sex
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Sex-linked diseases;
Haemophilia
 Colour-blindness
 Muscular dystrophy
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Inherited
Diseases
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Cystic Fibrosis.
Caused by recessive allele.
 Mainly people are carriers.
 Causes cells to produce sticky mucus. Results in
lengthy physio and higher infections rates.
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Huntington’s Disease.
Attacks the nervous system. Symptoms include
loss of muscle control and memory loss and
commence later in life.
 Caused by dominant allele.
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Ethical
Decisions
Amniocentesis is a test on an unborn baby
to detect if it has cystic fibrosis.
 It is not 100% reliable with a 0.5%
miscarriage risk, small chance of infection,
and results only between 15-18 weeks.
 Information could be used to decide on a
termination (abortion). This is an ethical
decision based on genetic testing
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Reliability of
Genetic Tests
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False-negative;
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Wrong result which says a person does not have a
medical condition but they do.
False-positive;
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Wrong result which says a person has a medical
condition but they do not (this could have been
aborted so ethics again!)
Designer babies
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Embryo selection (form of
IVF);
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Gametes fertilised in labs, and
then the embryo’s tested for
genetic disease/s (checking the
alleles). Healthy ones used for
mothers womb. What about the
others??
Gene therapy;
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Curing an inherited disease by
putting correctly working alleles
into a person.
Had limited success. Currently
illegal for sex cells. People
worried it could lead to control
features like eye colour, etc.
Cloning
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Clone is genetically identical to the organism it
was made from.
Happens naturally with identical twins and also
asexual reproduction (one parents such as
bacteria).
Early embryos are made of stem cells which can
develop into any specialised cell. Scientists want
to clone using cloned embryos. Ethical
decisions?
Arguments
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In favour;
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Scientific progress
Organ transplants
Legal up to 14 days
Your relation/friend?
Against;
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Human rights
Lowers value of life
‘Murder’ of embryos