1. 1
   A plant breeder repeats one of Mendel's crosses using garden peas (Pisum sativum). She removes the anthers from flowers of a pure-breeding tall variety and dusts their stigmas with pollen from a pure-breeding dwarf variety, then covers the flowers with bags. All the seeds from this cross grow into tall plants. She allows these tall plants to self-pollinate. Their seeds give 787 tall plants and 277 dwarf plants.

   (a)

   What is the genotype of the tall plants grown from the seeds of the first cross?

   [1 mark]

   • AHomozygous dominant
   • BHeterozygous
   • CHomozygous recessive
   • DHaploid, with one allele of the gene

   (b)

   Why did the breeder remove the anthers from the flowers of the tall variety before the cross?

   [1 mark]

   • ATo stop female gametes forming in the ovary
   • BSo that the offspring would be haploid
   • CTo make the tall allele dominant
   • DTo stop the flowers self-pollinating, as pea flowers produce both male and female gametes

   (c)

   Calculate the ratio of tall to dwarf plants in the F2 generation and deduce whether the result supports the hypothesis that the tall allele is dominant.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A woman has blood group A. Her father had blood group O. She and her partner, who has blood group AB, are expecting their first child. The ABO gene has three alleles in the human gene pool: $I^A$, $I^B$ and $i$.

   (a)

   What is the woman's genotype?

   [1 mark]

   • A$I^AI^A$
   • B$I^AI^B$
   • C$I^Ai$
   • D$ii$

   (b)

   Which blood groups are possible for the couple's child?

   [1 mark]

   • AA, B and AB only
   • BA and B only
   • CA, B, AB and O
   • DAB only

   (c)

   Distinguish between codominance and incomplete dominance, using the AB blood group and one other named example.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A student measures the heights of 11 classmates of the same age and sex. The heights in cm, in order, are: 158, 162, 165, 167, 168, 170, 171, 173, 176, 179 and 196. She calculates that the first quartile is 165 cm, the median is 170 cm and the third quartile is 176 cm, and she plans to display the data as a box-and-whisker plot.

   (a)

   Determine whether any of the heights is an outlier.

   [3 marks]

   (b)

   Explain why height in humans shows continuous variation and suggest why the student should summarise these data using the median rather than the mean.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   Haemophilia A is caused by a recessive allele of a gene for a blood-clotting protein carried on the X chromosome. In one family, an unaffected man (I-1) and an unaffected woman (I-2) have three children: a son with haemophilia (II-1), an unaffected daughter (II-2) and an unaffected son (II-3). The daughter II-2 has two children with an unaffected man (II-4): a son with haemophilia (III-1) and an unaffected daughter (III-2). III-2 is now planning a family with an unaffected man. Use $X^H$ for the normal allele and $X^h$ for the haemophilia allele.

   (a)

   Explain how sex is determined in humans and why haemophilia is inherited differently by the sons and daughters in this family.

   [6 marks]

   (b)

   Deduce the genotypes of I-2 and II-2, and determine the probability that a son and that a daughter of III-2 will have haemophilia.

   [6 marks]

   Total for question 4: 12 marks

End of questions