Chapter 26 - HKALE 1989 Biology Paper II(d The table below...

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HKALE 1989 Biology Paper II (d) The table below shows the genotypic frequency of the offspring of two dihybrid crosses I and II . (A, B, C, D and a, b, c, d represent the respective alleles involved.) Cross Parental genotypes Offspring Genotype Frequency I AbBb ×aabb AaBb aaBb Aabb aabb 25% 25% 25% 25% II CcDd ×ccdd CcDd ccDd Ccdd ccdd 46% 3% 4% 47% (i) Briefly discuss the genetic principle demonstrated in Cross I , and suggest how such genotypic frequencies in the offspring are obtained. (3 marks) ANS 3 (d)(i) AB Ab aB Ab (3) Ab AaBb Aabb aabb aabb Or 25% 25% 25% 25% This demonstrates Mendel’s Second Principle independent assortment of unlinked genes Both A and B (or the alleles) are located at 2 chromosomes to be assorted independently HKALE 1997 Biology Paper II 3. (a) What are the processes that generate genetic variations in flowering plants ? Explain the mechanisms involved. (6 marks) 3. (a) Meiosis in the formation of spores / pollen and embryo sac / male and female gametophytes. Crossing over at meiosis between homologous chromosomes results in reciprocal exchange of genetic material random assortment of chromosomes into daughter nuclei 2 Pollination and Fertilization are a random processes resulting in random combination of genetic make-up from the gametes.
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