Mendelian Genetics

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Mendelian Genetics
Aim To be able to construct and interpret
genetic diagrams.
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Genetics SPLAT
Heterozygous
Unspecialised
Chromosomes
DNA
Meiosis
Cancer
Allele
Gametes
Bone Marrow
Dominant
Downs Syndrome
Daughter Cells
Recessive
Amino Acids
Double Helix
Pancreas
Mitosis
Homozygous
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Genes, Chromosomes and DNA
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How genes work
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
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Mutations
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 Genetics
My name is Gregor Mendel. I am the father of
modern genetics because of the work I did on pea
plants in 1865
Mendels experiment
Take two plants one which is pure-bred for
tallness and one pure-bred for shortness, and
cross them
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Modern 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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Mendels Experiment
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Eye 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
bb
BB
Bb
Homozygous brown-eyed parent
Heterozygous brown-eyed parent
Blue-eyed parent
What would the offspring have?
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Eye colour
Example 1 A homozygous brown-eyed parent and a
blue-eyed parent
Example 2 2 heterozygous brown-eyed parents
X
X
Parents
Gametes
(FOIL)
Offspring
All offspring have brown eyes
25 chance of blue eyes
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Eye colour
Example 3 A heterozygous brown-eyed father and a
blue-eyed mother
Equal (50) chance of being either brown eyed or
blue eyed.
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Another method
Example 3 A heterozygous brown-eyed father and a
blue-eyed mother
Father
Mother
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Example 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 kittens genotype first).
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Genetics SPLAT
Heterozygous
Unspecialised
Chromosomes
DNA
Meiosis
Cancer
Allele
Gametes
Bone Marrow
Dominant
Downs Syndrome
Daughter Cells
Recessive
Amino Acids
Double Helix
Pancreas
Mitosis
Homozygous