1How do multiple alleles of a gene arise? (2 marks)
Random genetic mutations
At different positions in the gene
2What is meant by a recessive allele? (1 mark)
Only expressed if homozygous
3Meiosis results in cells that have the haploid number of chromosomes and show genetic variation. Explain how (7 possible marks)
Homologous chromosomes pair up / bivalents form
Crossing over / chiasmata form
Produces new combinations of alleles
Chromosomes separate
At random
Producing varying combinations of alleles
Chromatids separated at meiosis 2
4Explain why observed ratio of offspring phenotypes is different from expected (4 possible marks)
Fertilisation is random
Offspring ratios are a probability
Gametes may not be produced in equal numbers
Small sample
5Explain what is meant by a dominant allele (1 mark)
Always expressed
6Observed phenotypic ratios different from expected ratios. Explain why (5 possible marks)
Fertilisation is random
Small sample
Linked genes
Epistasis
Lethal genotypes
7What is meant by the term phenotype? (2 marks)
Genotype
Environment
8Explain what linked genes means (1 mark)
Same chromosome