1. In the process of meiosis, four haploid cells are formed. Explain what is meant by haploid.
Answer
A haploid cell has one set of chromosomes (half the number of the parent cell if the parent cell was diploid).
2. Meiosis generates a large amount of variation within gametes. Name the two processes that occur in meiosis that cause this variation.
Answer
Crossing over and independent segregation.
3. The table below shows the mRNA codons and the corresponding amino acid that they code for. Determine the amino acid sequence for the following DNA strand: TAC, GTA, GTA, TCA, CCT, CAT, CGC, ATT.
Answer
Met, His, His, Ser, Gly, Val, Ala, STOP.
4. Describe and explain how the process shown in the figure below increases variation.
Answer
The process shown in the figure is called crossing over. It occurs between non-sister chromatids of a homologous pair of chromosomes, where equal sections of DNA are exchanged. This creates a new combination of alleles.
5. The figure below shows the process of meiosis in an organism with a diploid number of four. Describe and explain the relationship between the chromosomes labelled X.
Answer
Homologous chromosomes that may have different alleles.
6. Complete the figure above to show four gametes that could be produced at the end of meiosis.
Answer
7. Give the number of different gametes that can be produced in the organism above through independent assortment alone. Explain why the actual number of genetically different gametes is much greater than this.
Answer
The number of gametes that can be produced through independent assortment alone is
8. Name another source of genetic variation in organisms that does not occur during the cell cycle.
Answer
Random fertilisation.
9. The figure below shows the karyotype of a person born with Edwards Syndrome. Give the cause of Edwards syndrome. What is the cause of this mutation ?
Answer
Three copies of chromosome number 18 (Trisomy 18). The cause is non-disjunction mutation.
10. Describe how events in meiosis can lead to Edwards syndrome.
Answer
During the first or second meiotic division (anaphase I or II), the chromatids of chromosome 18 are not separated; instead, both chromatids move to the same pole by the spindle fibres. As a result, one cell contains two chromatids, while the other contains none for chromosome 18.