1. What is "asexual reproduction" ?
Answer
Reproduction that only involves one parent and no fusion of gametes.
2. What does each gene code for ?
Answer
Each gene codes for a particular sequence of amino acids, to make a specific protein.
3. How many bases are needed to code for one amino acid ?
Answer
Three bases are required to code for an amino acid.
4. Human body cells have 46 chromosomes, but gametes only have 23 chromosomes. Explain why it is important for gametes to have 23 chromosomes.
Answer
The female gamete (egg) and male gamete (sperm) fuse together so the 23 chromosomes from each restore the cell to 46 chromosomes.
5. Explain why it is an advantage for a malaria parasite to reproduce sexually.
Answer
In sexual reproduction there is mixing of genetic information that leads to leads to genetic variation. The offspring may be better adapted to survive if the environment changes to become less favourable.
6. The order of bases in DNA controls how proteins such as enzymes are made. Describe how the DNA base sequence is used to produce a specific enzyme.
Answer
The order of bases controls the order in which amino acids are assembled. A sequence of three bases is the code for one particular amino acid. Proteins are synthesised on ribosomes according to a template of the gene. Carrier molecules bring specific amino acids to join to the growing protein chain in the correct order. When the protein chain is complete it folds up to form the specific shape of the protein (or enzyme).
7. Define the term "allele".
Answer
An allele is a different form of a gene, or a different version of the same gene.
8. Fur colour in mice is controlled by a single gene, where G = grey fur and g = white fur. A heterozygous male breeds with a homozygous recessive female. Determine the probability that their offspring will have white fur.
Answer
From the Punnett square below, the offspring genotypes are 50% Gg and 50% gg. The probability is 0.5
9. Cystic fibrosis (CF) is an inherited disorder caused by a recessive allele. If A = allele for normal health and a = allele for CF, what is the probability of two healthy carriers of the CF allele having a child who is also a healthy carrier of the CF allele ?
Answer
From the Punnett square below, the offspring’s genotypes are aa, Aa, Aa, aa. Offspring with the genotype aa are identified as having CF, and the probability is 0.5
