How Meiosis Causes Variation (5.1.2)

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What are the two ways that meiosis causes variation?
Crossing over, and independent assortment of chromosomes.
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Where does crossing over occur?
Prophase in meiosis I.
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What is crossing over?
Non-sister chromatids from a bivalent pair of chromosomes get tangled up. They form chiasmata- the chromatids break & rejoin to the other chromosome, producing different allele combinations. This separates genes that are usually linked together.
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Where does independent assortment occur?
Metaphase in meiosis I.
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What is independent assortment?
Either chromosome in each pair can be on top or underneath when they line up at the equator of the cell. This mixes up the alleles from the maternal and paternal chromosomes.
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Describe what is meant by homologous pairs.
They carry the same sequence of genes along their length, each gene being found at a specific location on the chromosome, called a locus.
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Why do we never look exactly like our parents or siblings?
In a normal human cell carrying out meiosis, the number of different combinations possible is 2^23.
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Card 2

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Where does crossing over occur?

Back

Prophase in meiosis I.

Card 3

Front

What is crossing over?

Back

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Card 4

Front

Where does independent assortment occur?

Back

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Card 5

Front

What is independent assortment?

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