DNA, genes and the genomeIB MYP Biology: Subtopic test

1. 1
   A science museum in Dubai has built a large model of DNA for visitors to explore. The model shows two long strands twisted around each other, with the strands joined together in the middle by pairs of bases.

   (a)

   Which term describes the shape of the DNA molecule?

   [1 mark]

   • AA single spiral
   • BA zigzag chain
   • CA closed ring
   • DA double helix

   (b)

   Which pair of bases joins the two strands of DNA together?

   [1 mark]

   • AA with C
   • BA with T
   • CG with T
   • DC with A

   (c)

   Distinguish between a gene and the genome.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A student in Manila extracts DNA from strawberries in a school laboratory. She mashes the fruit, adds a mixture of salt and washing-up liquid, filters it, and then carefully pours ice-cold ethanol on top of the filtered liquid. White, stringy strands slowly appear where the two liquids meet.

   (a)

   What is the main purpose of adding washing-up liquid in the extraction?

   [1 mark]

   • ATo break down the cell membranes so that the DNA is released
   • BTo cool the mixture
   • CTo make the DNA insoluble
   • DTo cut the DNA into separate genes

   (b)

   Why does the DNA appear as white strands when the cold ethanol is added?

   [1 mark]

   • AThe ethanol dissolves the DNA completely
   • BThe ethanol kills bacteria in the fruit
   • CThe DNA is not soluble in cold ethanol, so it comes out of solution
   • DThe ethanol breaks the DNA into single bases

   (c)

   Explain why the student mashes the fruit and then filters the mixture.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A genetic counsellor in Cape Town explains to a family that every human body cell has a nucleus containing chromosomes made of DNA, and that a change in a gene can sometimes cause an inherited disorder.

   (a)

   State the number of chromosomes in a human body cell and describe how chromosomes, genes and DNA are related.

   [3 marks]

   (b)

   Explain what a mutation is and describe how a mutation in a gene could affect the protein it codes for.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A hospital in Singapore ran a pilot study in which DNA was extracted from a few drops of blood from 2000 newborn babies and the sequence of bases in their genes was read. Doctors were looking for mutations linked to serious disorders that can be treated if found early. A harmful mutation was found in 18 babies, and all 18 started treatment in their first month. A change in the DNA of unknown effect was found in 140 other babies; their families were worried for several months, but later tests showed the changes were harmless. The hospital is now considering offering this genome test to every newborn.

   (a)

   Process the data and evaluate whether the pilot study supports offering the genome test to every newborn.

   [6 marks]

   (b)

   Discuss whether the hospital should offer genome sequencing to every newborn.

   [6 marks]

   Total for question 4: 12 marks

End of questions