1. Describe the structure of DNA.
Answer
DNA is a polymer made up of two strands forming a double helix.
2. What is the "genome" of an organism ?
Answer
The genome is the complete set of genetic information of an organism.
3. What is "polydactyly" ?
Answer
A genetic disorder causing extra fingers or toes.
4. A fertilised egg cell develops into a ball of cells called an embryo. Explain what happens to the fertilised egg cell as it develops into an embryo.
Answer
The fertilised egg divides by mitosis and the number of cells increases. As the embryo develops, the cells differentiate.
5. DNA is a polymer. Polymers are made up of repeating units. Name the repeating units in DNA.
Answer
The repeating units are called nucleotides.
6. A mutation occurs in a gene and causes a change in one amino acid of an enzyme. Explain how a change in one amino acid could produce an enzyme that does not work properly.
Answer
The different amino acid could alter the protein so that it has a different shape. This changes the shape of the active site, so the substrate can no longer fit or bind.
7. Describe the alleles that must be present for a recessive trait to be expressed in the phenotype of an organism.
Answer
A recessive trait is expressed when no dominant allele is present, or when two copies of the recessive allele are present.
8. Sickle cell disease (SCD) in humans is a blood disorder controlled by a single gene and caused by a recessive allele. A male carrier has a child with a female who has sickle cell disease. Explain why the child may also be a carrier of SCD.
Answer
The child may inherit a recessive allele from his father, but since he does not have SCD, he must have inherited a dominant allele from his mother.
9. Suggest some reasons why people might be in favour of embryo screening.
Answer
Embryo screening can prevent a child from having cystic fibrosis or another inherited disorder, reduce the long-term costs of caring for a child with CF, prevent future suffering for the child and family, provide embryos that may be used for stem cell research or treatment, and reduce the number of alleles for CF in the gene pool.