O-LevelBiologyGenetics & Variation5090/21 · Oct/Nov 2014 · Q810 Marks
Explain how meiosis is involved in the formation of gametes.
- (a)(i)Explain how meiosis is involved in the formation of gametes.[2]
- (a)(ii)Explain how two plants, one with red flowers and one with white flowers, can produce seeds that will grow into plants with either red or white flowers in the ratio of 1:1.[6]
- (b)Suggest how two plants, of a different species, one with red and one with white flowers, could produce seeds that will grow into plants with pink flowers.[2]
Mark scheme
Marking points from the official mark scheme (Oct/Nov 2014). The mark or mark type is shown in brackets.
- [max. 2] in testes / anthers / ovaries ;
- [max. 2] cell division;
- [max. 2] halving of chromosome numbers/haploid ;
- [max. 2] so that diploid number is restored on fertilisation ;
- [max. 6] one (either) colour is controlled by a dominant allele;
- [max. 6] one by a recessive allele ;
- [max. 6] one parent heterozygous – (or described, e.g. Rr) ;
- [max. 6] one is homozygous recessive (or described) ;
- [max. 6] correct ref. to gametes ;
- [max. 6] gametes correctly identified for both parents ;
- [max. 6] how gametes pair to produce offspring in 1:1 ratio ;
- [max. 2] mutation;
- [max. 2] ref to a named mutagen ;
- [max. 2] possible co-dominance ;
- [max. 2] ref. to heterozygous plants having pink flowers ;
- [max. 2] ref availability of certain ions (as in Hydrangea);
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