3.4.3 - Genetic diversity due to mutations or meiosis Flashcards

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1
Q

Define gene mutation

A

change in the base sequence of chromosomes - can arrise spontaneously during DNA replication and include base deletion and substitution

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2
Q

How does base substitution result in a different amino acid sequence ?

A
  • polypeptide produced will differ by one amino acid
  • Two impacts:
  • 1- if the amino acid is** changed** and is involved in forming bonds final protein may be a different shape and not function properly
  • 2 - amino acid may not be changed as genetic code is **degenerate **- so polypeptide produced will not be effected
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3
Q

How does base deletion result in a different amino acid sequence?

A
  • entire amino acid sequence will be changed so polypeptide will not function correctly
  • as every triplet has been shifted to the left by one base (so is read incorrectly)
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4
Q

Define chromosome mutation - what are the two types

A

changes to the number or structure of chromosomes
1. polyploidy - changes in whole sets of chromosomes (eg three or more instead of two)
2. non-disjunction - homologous pairs don’t separate in meiosis so gamete has one more or one less chromosome - **number of individual chromosomes is changed **

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5
Q

Define meiosis

A

produced four genetically different haploid daughter cells

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6
Q

Describe the process of meiosis

A
  1. First division (meiosis 1) - homologous chromosomes pair and chromatids wrap around - exchanged during** crossing over** -
  2. Second division (meiosis 2) - chromatids move apart and four haploid cells are formed (each with 23 chromosomes)
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7
Q

How is genetic variation achieved during meiosis?

A
  1. independent segregation - homologous pairs line up at random during meiosis one which results in a random combination of chromosomes going into each daughter cell
    2.** crossing over** of maternal and paternal alleles
    - chromatids (of homologous chromosomes) twist around each other
    - tension - sections of chromatid break off and join to sections of the partner chromosome (RECOMBINATION)
    - results in new genetic combinations in the maternal and paternal alleles
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8
Q

How can you calculate the number of possible combinations of chromosomes in a daughter cell

A

2^n (where n is the number of PAIRS of homologous chromosomes)

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9
Q

How can you calculate the possible number of
different combinations of chromosomes
following** random fertilisation of two
gametes?**

How would crossing over and recombination impact this value?

A

( 2 ^n ) ^2
- random fertilisation of haploid gametes further increases genetic variation within a species

increase the number of possible chromosome combinations

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