Mutations and Meiosis Flashcards
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Define the term mutagenic agent (1 mark).
A factor that increases the rate of mutations.
Name the type of mutation that changed the number of chromosomes in S. townsendii to produce S. anglica and explain your answer (3 marks).
Name: Non-disjunction.
Explanation: Occurs in meiosis; chromosomes fail to separate or all move to one cell.
Explain one other way genetic variation within a species is increased apart from mutation (2 marks).
Random fertilisation produces new allele or chromosome combinations.
What is the amino acid sequence determined by the DNA template AGG CGT CCT GGA? (1 mark)
Serine, Alanine, Glycine, Proline.
Does the information support the student’s conclusion about the mutation involving addition of one nucleotide? (2 marks)
No; substitution not addition occurred, or if it were addition, a frameshift would affect more than one amino acid.
Why are trout eggs produced by meiosis genetically different? (1 mark)
Because of independent segregation or crossing over.
Why are offspring from farmed trout sterile? (2 marks)
They have an extra set of chromosomes; homologous chromosomes can’t pair, so meiosis doesn’t occur.
Define gene mutation and give a reason for no effect and a reason for positive effect (4 marks)
Mutation = change in DNA base sequence forming a new allele.
No effect: degenerate code or intron mutation.
Positive: change improves protein or survival.
Give two differences between mitosis and meiosis (2 marks)
Mitosis: one division, identical cells.
Meiosis: two divisions, genetically different cells.
How many chromatids are present in the zygote? (1 mark)
28
What can you conclude about chromosome movement in meiosis in this fungus? (3 marks)
Homologous chromosomes separate randomly; crossing over is rare—only seen in 10 tubes.
What is the minimum number of bases in a gene for 465 amino acids? (1 mark)
1395 bases.
Which DNA mutation results in Val to Ala at amino acid 203? (1 mark)
CAA → CGA.
Explain why a Glu to Lys mutation at amino acid 300 had no effect but one at 279 did (3 marks)
Both are charged, but 279 change affects active site shape or bonding. 300 doesn’t alter tertiary structure.
What is the chromosome content of daughter cells from normal meiosis? (2 marks)
1 long and 1 short chromosome in each first division cell; 1 long and 1 short (separate) in second division.
Give expected number of plants producing 2n gametes after cycle 1 (2 marks)
Expected: 52 did not produce; 4 did produce 2n gametes.
What process produced the allele combination in the first polar body? (1 mark)
Crossing over.
How many mitochondria are in the polar body? (2 marks)
Approximately 33.
Which letter shows where meiosis occurs in moss life cycle? (1 mark)
D.
Explain how the chromosome number is halved during meiosis (2 marks)
Homologous chromosomes pair; one of each pair goes to opposite poles.
What is the haploid number in this moss? (1 mark)
6
Describe crossing over and how it increases diversity (4 marks)
Homologous chromosomes form bivalents, chiasmata form, chromatids exchange alleles, creating new combinations.
What is the effect of Patau syndrome on chromosomes? (1 mark)
Extra chromosome 13 (trisomy 13).
Describe how this chromosome change in Patau syndrome occurred (2 marks)
Non-disjunction in meiosis; chromosomes failed to separate.
Why do all cells in Patau syndrome have the mutation? (2 marks)
Mutation in gamete forming zygote; all cells derived by mitosis.
