DNA, genes and inheritanceIB MYP Sciences: Subtopic test

1. 1
   A science museum in Seoul has an exhibit about the nucleus of a human body cell. It explains that the nucleus contains 46 chromosomes arranged in 23 pairs, and that each chromosome is made of one very long molecule that is tightly coiled.

   (a)

   Which molecule makes up the chromosomes and carries the genetic information?

   [1 mark]

   • AStarch
   • BDNA
   • CGlycogen
   • DLipid

   (b)

   Which statement describes a gene?

   [1 mark]

   • AA complete set of all the chromosomes in a cell
   • BA different version of the same section of DNA
   • CA section of DNA that carries the instructions for a characteristic
   • DA cell that stores genetic information

   (c)

   Explain what is meant by the term allele and why a body cell contains two alleles of each gene.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A pet breeder in Brazil crosses two hamsters that both have black fur. Black fur is controlled by a dominant allele (B) and brown fur by a recessive allele (b). Some of the offspring in the litter have brown fur.

   (a)

   What can be deduced about the genotypes of the two black parents?

   [1 mark]

   • ABoth are homozygous dominant (BB)
   • BOne is BB and the other is Bb
   • CBoth are homozygous recessive (bb)
   • DBoth are heterozygous (Bb)

   (b)

   Which term describes the genotype of the brown hamsters?

   [1 mark]

   • AHomozygous recessive
   • BHeterozygous
   • CHomozygous dominant
   • DCodominant

   (c)

   Use a Punnett square to show the cross between the two black parents, and state the ratio of black to brown offspring that is expected.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A genetic counsellor in Toronto meets a couple who do not have cystic fibrosis, but whose first child does. Cystic fibrosis is caused by a recessive allele (f). The dominant allele (F) allows the body to work normally.

   (a)

   Explain how two parents who do not have cystic fibrosis can have a child who has the condition.

   [3 marks]

   (b)

   Determine the probability that the couple's next child will have cystic fibrosis, and the probability that the next child will be a carrier. Show your working.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A hospital in Cyprus offers free blood tests to couples planning a family, to find out whether they carry the recessive allele for thalassaemia, a serious inherited blood condition. A child has the condition only if they inherit two copies of the allele. Over several years the hospital records 80 children born to couples who were both carriers: 17 had thalassaemia, 41 were carriers without the condition and 22 had no copy of the allele.

   (a)

   Evaluate whether the hospital's results agree with the prediction for children of two carrier parents.

   [6 marks]

   (b)

   Discuss and evaluate the hospital's programme of testing couples to find out whether they are carriers.

   [6 marks]

   Total for question 4: 12 marks

End of questions