With reference to the inheritance of blood groups, explain what is meant by each of the following terms:

Mark scheme

Marking points from the official mark scheme (May/June 2016). The mark or mark type is shown in brackets.

1. [max 3] 1. allele(s);
2. 2. responsible for a character(istic)/trait ;
3. 3. only one needs to be present/reference to heterozygote AW ;
4. 4. for the character to appear/be expressed (in phenotype) AW ;
5. 5. e.g. IAIO + group A/IBIO + group B/IAIB + dominant to IO ; A A, B, O instead of IA, IB, IO
6. [max 3] 1. two alleles ;
7. 2. neither being recessive/(equally) dominant;
8. 3. both have an effect/are expressed/phenotype intermediate ;
9. 4. reference to heterozygote AW ;
10. 5. IAIB/AB;
11. [max 4] 1. number of chromosomes in a gamete is half those in a somatic or body cell ORA/one versus two sets of chromosomes ; A sex cell = gamete/one named gamete
12. 2. correct use of the terms haploid + diploid;
13. 3. 46 v. 23;
14. 4. gametes/haploid cells are the result of meiosis/reduction division;
15. 5. somatic/body cells occur in/produced by mitosis;
16. 6. (diploid) number restored + at fertilisation;
17. 7. each parent has equal share in genotype of offspring AW;