A3 - G, A + I Q.s
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1
How do multiple alleles of a gene arise? (2 marks)
Random genetic mutations
At different positions in the gene
At different positions in the gene
2
What is meant by a recessive allele? (1 mark)
Only expressed if homozygous
3
Meiosis 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
Crossing over / chiasmata form
Produces new combinations of alleles
Chromosomes separate
At random
Producing varying combinations of alleles
Chromatids separated at meiosis 2
4
Explain 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
Offspring ratios are a probability
Gametes may not be produced in equal numbers
Small sample
5
Explain what is meant by a dominant allele (1 mark)
Always expressed
6
Observed phenotypic ratios different from expected ratios. Explain why (5 possible marks)
Fertilisation is random
Small sample
Linked genes
Epistasis
Lethal genotypes
Small sample
Linked genes
Epistasis
Lethal genotypes
7
What is meant by the term phenotype? (2 marks)
Genotype
Environment
Environment
8
Explain what linked genes means (1 mark)
Same chromosome
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