Explain how meiosis can lead to genetic variation.

Mark scheme

Marking points from the official mark scheme (Oct/Nov 2017). The mark or mark type is shown in brackets.

1. [8] eight from: 1 chiasmata formation; 2 crossing over ; 3 exchange of genetic material; 4 between non-sister chromatids of homologous chromosomes ; 5 at prophase 1; 6 new combination of alleles ; 7 linkage groups broken; 8 independent / random, assortment, of homologous pairs / bivalents / AW ; 9 in metaphase 1; 10 2ⁿ combinations / very large number of combinations; 11 independent / random, assortment of, chromatids / chromosomes (correct context); 12 in metaphase 2; 13 ref. to mutation;
2. [7] seven from: 1 ref. to TYR gene; 2 normal gene product is tyrosinase ; 3 tyrosine converted to, DOPA / dopaquinone ; ora 4 melanin / pigment, made ; ora 5 in melanocytes ; 6 mutant allele is recessive ; 7 tyrosinase, not produced / inactive; 8 affects, hair / skin / irises; 9 only in homozygous recessive people;