TOPIC 10 GENETICS

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TOPIC 10 GENETICS
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10.1 Meiosis (overview)
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Prophase I of Meiosis I
10.1.1 Describe the behaviour of the chromosomes
in the phases of meiosis.
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Metaphase I of Meiosis I
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Anaphase I of Meiosis I
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Telophase I of Meiosis I
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Prophase II of Meiosis II
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Metaphase II of Meiosis II
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Anaphase II of Meiosis II
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Telophase II of Meiosis II
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10.1.2 Crossing over
10.1.2 Outline the formation of chiasmata in the
process of crossing over.
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10.1.2 Crossing over
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10.1.3 Explain how meiosis results in an
effectively infinite genetic variety in gametes
through crossing over in prophase I and random
orientation in metaphase I.
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10.1.3 and 10.1.4
10.1.3 and 10.1.4. State Mendels law of
independent assortment.
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10.2 Dihybrid Crosses and gene linkage

• Unlinked
• genes

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10.2.1 Calculate and predict the genotypic and
phenotypic ratio of offspring of dihybrid crosses
involving unlinked autosomal genes.
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10.2.2 autosomes / sex chromosomes
10.2.2 Distinguish between autosomes and sex
chromosomes.
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10.2.3 Crossing over
10.2.3 Explain how crossing over between
non-sister chromatids of a homologous pair in
prophase I can result in an exchange of alleles.
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A pair or set of genes on a chromosome that tend
to be transmitted together.
10.2.4 Define linkage group.
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10.2.5 and 10.2.6
10.2.5 and 10.2.6 Explain an example of a cross
between two linked genes.
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10.2.5 and 10.2.6
Identify which of the offspring are recombinants
in a dihybrid cross involving linked genes.
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Polygenic Inheritance
10.3.1 Define polygenic inheritance.
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10.3.2 Explain that polygenic inheritance can
contribute to continuous variation using two
examples, one of which must be human skin colour.
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BIG PICTURE of MEIOSIS
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LINKED GENES
X
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AaBb
A
a
A
a
?
OR
B
b
B
b
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Start by assuming that the genes are unlinked
because you know what would be the expected
ratios of offspring AaBb
A a B b
AB
Ab
aB ab
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AaBb x AaBb
A a B b
AB
Ab
aB ab
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AaBb x AaBb
A a B b
AB
Ab
aB ab
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AaBb
A a B b
AB
Ab
aB ab
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AaBb X
AaBb
A a B b
A a B b
AB
Ab
aB ab
AB
Ab
aB ab
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AB Ab aB
ab AABB AABb
AaBB AaBb AABb
Aabb AaBb
Aabb AaBB AaBb
aaBB aaBb AaBb Aabb
aaBb aabb
AB Ab aB ab
A______ B_____ 9/16 1125 620 A______ bb
3/16 375 702 aa B_____
3/16 375 503 aa bb
1/16 125 400
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What are the expected phenotype ratios if the
genes are unlinked in the following crosses? Then
determine if the genes appear to be linked or
unlinked AABb X AAbb AaBB X
aaBb aaBb X Aabb
Expected Observed
A__B__ 500
aaB__ 500
A__bb 500
aabb 500
Expected Observed
A__B__ 980
aaB__ 1020
A__bb 0
aabb 0
Expected Observed
A__B__ 324
aaB__ 562
A__bb 417
aabb 697