Genetic Variation

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14 Terms

1
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What are alleles?

Different versions of the same gene

2
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Which two processes in meiosis increase genetic variation?

  • Crossing over

  • Independent segregation

3
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How do both crossing over and independent segregation increase genetic variation?

By producing new allele combinations

4
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What does independent segregation involve?

Homologous chromosomes lining up randomly during meiosis

5
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What does crossing over involve?

  • Homologous chromosomes wrap around each other

  • Chromatids exchange alleles

6
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How do you calculate the number of possible chromosome combinations following meiosis?

2n , where n is the number of pairs of homologous chromosomes

7
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What is a chromosome mutation?

A mutation that leads to meiosis producing cells with an abnormal number of chromosomes (different to the haploid number)

8
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What is an example of a chromosome mutation?

Non-disjunction

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What is the difference between non-disjunction in meiosis I and non-disjunction in meiosis II?

In meiosis I, a pair of homologous chromosomes doesn’t separate properly. In meiosis II, a pair of sister chromatids doesn’t separate properly

10
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What do the gametes look like after non-disjunction has taken place during meiosis I?

Two gametes have an extra chromosome, two gametes have a missing chromosome

11
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What do the gametes look like after non-disjunction has taken place during meiosis II?

One gamete has an extra chromosome, one gamete has a missing chromosome, two gametes have the correct number of chromosomes

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What could non-disjunction lead to? Give an example.

Could lead to a genetic condition in offspring such as Down’s syndrome

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Why does fertilisation lead to genetic variation?

It is random- any two gametes may fuse

14
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How do you calculate the number of possible chromosome combinations following random fertilisation?

(2n)2