Role of Mutation • Change in structure or amount of an organism’s genetic material • Change in genotype produces change in phenotype = mutant • 2 types of mutation . ۱ Chromosome mutation . ۲ Change in structure of one chromosome
Chromosome mutations • Change in chromosome number . ۱ Non-disjunction in meiosis . ۲ Non-disjunction of sex chromosomes . ۳ Complete non-disjunction and polyploidy
Non-disjunction during meiosis • Spindle fibre fails during meiosis • Members of one pair of homologous chromosomes fail to become separated • 2 gametes receive extra copy of affected chromosome • 2 gametes lack that chromosome
Down’s Syndrome r Non-disjunction in chromosome 21 r Occurs in human egg mother cell r One or more abnormal eggs formed (n = 24) r Fertilised by normal sperm (n = 23) r Formation of abnormal zygote (2n = 47)
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