GCSE AQA Biology 1 Variation, Genetics & Reproduction

GCSE AQA Biology 1 Variation, Genetics & Reproduction

1. Variation

   • Genetic
     • Characteristics similar to parents'
       • Genes inherited from parents
     • Some genes from mother, some from father
     • No 2 members of species identical (apart from identical twins)
   • Environmental
     • Differences that have been caused by conditions organism lives in
   • Characteristics affected by genetic & environmental factors...

2. Genes, chromosomes and DNA

   • Cells have nucleus - contains genetic info in form of chromosomes
     • Human cell nucleus contains 23 pairs of chromosomes
       • Chromosomes carry genes - genes control development of different characteristics
         • Gene is short length of chromosome, which is long length of DNA - can be diffferent versions of same gene (alleles)
           • DNA coiled up to form arms of chromosome

3. Sexual reproduction

   • Fusion of male & female gametes - 2 parents so offspring contain mixture of parents' genes
     • Each gamete contains 23 chromosomes
       • When fertilised, form cell with full number of chromosomes
   • Offspring inherits features from both parents - produces variation

4. Asexual reproduction

   • Only 1 parent
   • No fusion of gametes
   • No mixing of chromosomes/no genetic variation
   • Offspring are genetically identical (clones)
   • How plant & animals grow/produce replacement cells
   • Some organisms produce offspring using asexual reproduction (bacteria & certain plants)

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