1. Gene mutations occur when the base sequence in a gene changes during DNA replication. Some mutations have no impact on the polypeptide that they code for. Suggest two possible explanations for this.
Answer
A codon may change to another codon that codes for the same amino acid because the genetic code is degenerate. Some mutations do not alter the tertiary structure, as the substituted amino acid does not affect or participate in any hydrogen, ionic, or disulfide bonds. Therefore, it has no impact on the overall shape of the polypeptide.
2. Sometimes chromatids fail to separate properly during meiosis. What term is used to describe this ? What is the effect of this on the gametes made ?
Answer
This is called non-disjunction. This results in a gamete having more than the haploid number of chromosomes or a chromosome missing.
3. Explain what is meant by the term homologous chromosome.
Answer
Chromosomes that have the same genes at the same loci but may possess different alleles for those genes.
4. The table below shows two mutations of the original sequence. Name the type of mutation shown.
Answer
Substitution.
5. Describe and explain the consequences of the mutations above.
Answer
Mutation 1: has no effect on the polypeptide chain. Due to the degenerate nature of the code, it still codes
for His.
Mutation 2: will cause the polypeptide to be shorter. Because the mutation causes a STOP codon to be coded for, so no more amino acids will be added.
6. The figure below shows the life cycle of one kind of fungus. Place an X to indicate where meiosis is taking place.
Answer
7. Explain why the life cycle shown above provides very little variation between parent cell and gametes.
Answer
Gametes are created through mitosis, which generates clones (or identical cells).
8. The figure below shows a cell at the start of meiosis. Describe the appearance of one possible daughter cell at the end of the first division of meiosis.
Answer
Three chromosomes present, one from each pair. Each consists of two chromatids.
9. The figure below shows the life cycle of bracken fern. Complete the empty circles to show which stages are haploid (n) or diploid (2n).
Answer
