Page 19 - CB1.3 Genetic Varation sciPAD

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CB 1.3 GENETIC VARATION
PRINCIPLES OF GENETIC VARIATION
Meiosis as a Cause of Variation
Meiosis produces genetic variation - it’s the reason why you don’t look identical to other members
of your family. There are two important steps occurring during meiosis that cause this variation.
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Crossing Over
Independent Assortment
When homologous pairs of chromosomes line up during meiosis, they do so randomly (i.e. in no
particular order). This means it is completely random which combination of alleles end up in a
particular gamete. In humans, independent assortment of our 23 pairs of chromosomes means
there are over 8 million possible combinations!
Homologous chromosomes
pair up.
Parts of neighbouring
chromosomes cross over.
Crossed over sections of
chromosomes (and therefore
alleles) are exchanged.
Each gamete produced
may have different
combinations of alleles.
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The same four chromosomes line up randomly.....
like this..... or like this.
this......or......this.
Resulting in gametes
that look like.....
1. Explain how cell division by meiosis leads to genetic variation. 















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