DNA and Meiosis

Question 1

Explain how a change in sequence of DNA bases could result in a non-functioning enzyme

Answer 1

• Change in primary structure
• Change in hydrogen/ionic/disulfide bonds
• Alters tertiary structure/active site (of enzyme)
• No enzyme-substrate complexes form

Question 2

Define “allele”

Answer 2

(different) form/type/version of a gene/different base sequence of a gene

Question 3

Explain the ‘X’ shape of a chromosome

Answer 3

• Two/sister chromatids
• Due to DNA replication
• Joined by a centromere

Question 4

Give reasons why there are more genes than the minimum amount of genes that code for set amounts of amino acids

Answer 4

• Start/stop codons
• Non coding DNA/introns/multiple repeats/junk DNA
• Two chains/a non-coding strand/complementary base pairs
• Addition of bases by mutation

Question 5

Why might homologous chromosomes not be genetically identical despite carrying the same genes

Answer 5

They carry different alleles

Question 6

Describe the role of independent segregation in meiosis

Answer 6

• To provide genetic variation
• Allows different combinations of maternal and paternal chromosomes/alleles
• To produce haploid cells/half the chromosome number
• Allows homologous chromosomes/pairs to arrange randomly at the equator of the cell

Question 7

How is the structure of DNA related to its function?

Answer 7

• sugar-phosphate (backbone)/double stranded/helix provides strength
• Long molecule so can store lots of information
• Helix/coiled so compact
• Base sequence codes for amino acids/proteins
• Double stranded so strands can act as templates for replication
• Complementary base pairing so accurate replication
• (weak) hydrogen bonds for unzipping/strand separation
• many hydrogen bonds so stable/strong