1. Which type of cell division produces identical cells, and which type produces non-identical cells ?
Answer
Mitosis produces identical cells, while meiosis does not.
2. Where is DNA contained in eukaryotic cells ?
Answer
DNA is contained in structures called chromosomes found in the nucleus of a cell.
3. What does a nucleotide consist of ?
Answer
Each nucleotide consists of a common sugar and phosphate group with one of four different bases attached to the sugar.
4. How many pairs of chromosomes does an ordinary human body cell contain ?
Answer
Humans have twenty-three pairs of chromosomes.
5. Describe some advantages of asexual reproduction compared to sexual reproduction.
Answer
Asexual reproduction is faster than sexual reproduction. Only one parent is needed. It is more energy-efficient than sexual reproduction, as there is no need to find a mate. It produces many genetically identical offspring when conditions are favourable.
6. The figure below shows the structure of a small section of DNA. Identify the parts labelled X and Y.
Answer
7. Not all parts of DNA code for proteins. Explain the importance of these non-coding parts of DNA.
Answer
Non-coding parts can switch genes on and off, so variations in these areas of DNA may affect gene expression.
8. Fur colour in mice is controlled by a single gene. The allele for white fur is recessive, and the allele for grey fur is dominant. When a white male mouse breeds with a white female mouse, explain why all of the offspring are white.
Answer
No dominant allele is present, or only recessive alleles are present.
9. Sickle cell disease (SCD) in humans is a blood disorder controlled by a single gene and caused by a recessive allele. A male who is not a carrier of SCD has a child with a female who has sickle cell disease. If D = allele for normal health and d = allele for sickle cell disease, determine the probability that these individuals will have a child with SCD.
Answer
From the Punnett square below, the offspring’s genotype is Dd, the phenotype is unaffected, and the probability is 0.
10. Suggest some reasons why people might object to embryo screening.
Answer
Embryo screening is expensive, embryos cannot give consent, and it involves the destruction of embryos, which are considered potential human lives.