Chapter 8 DNA and Meiosis:
Common Exam Questions and Model Answers
Define allele
A form of a gene
Define gene
A section of DNA ; that codes for a polypeptide
What is the maximum number of amino acids this sequence of bases could code for?
Count bases and divide by 3
Why might this sequence of bases code for fewer amino acids?
Presence of introns; start triplet code
How is the structure of DNA related to its function?
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Sequence of bases determines sequence of amino acids
3 bases code for one amino acid
Sugar phosphate backbone for stability
Hydrogen bonds for strength but can be broken to replicate DNA
How is DNA different in a prokaryote compared to a eukaryote?
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Prokaryote = no proteins / Eukaryote = histone proteins
Prokaryote = shorter / Eukaryote = longer
Prokaryote = circular / Eukaryote = linear
Explain how a change in the DNA base sequence / mutation might result in a different protein / enzyme
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Change in primary structure (do NOT say different amino acids are MADE / FORMED – they are
coded for not formed)
Change in position of hydrogen / disulphide bonds
Change in tertiary structure /active site (only if question is asking about enzyme)
If enzyme: Substrate no longer complementary to active site
How does meiosis lead to genetic variation?
If just 2 marks:
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Crossing over
Independent segregation of homologous chromosomes.
If more than 2 marks you will need to explain these 2 concepts
Crossing over:
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Homologous chromosomes pair up
Crossing over occurs
Produces new combination of alleles
Independent segregation of homologous chromosomes:
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Homologous chromosomes separate
At random
Producing varying combination of alleles
Why is meiosis important?
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Maintains chromosome number (produces haploid gametes which join at fertilisation to form a
diploid zygote)
Leads to variation (some offspring better adapted to changing environments, leading to evolution)