GCSE AQA Biology 1 Variation, Genetics & Reproduction

Variation
1. Genetic
  1. Characteristics similar to parents'
    1. Genes inherited from parents
  2. Some genes from mother, some from father
  3. No 2 members of species identical (apart from identical twins)
2. Environmental
  1. Differences that have been caused by conditions organism lives in
3. Characteristics affected by genetic & environmental factors...
Genes, chromosomes and DNA
1. Cells have nucleus - contains genetic info in form of chromosomes
  1. Human cell nucleus contains 23 pairs of chromosomes
    1. Chromosomes carry genes - genes control development of different characteristics
      1. 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
Sexual reproduction
1. Fusion of male & female gametes - 2 parents so offspring contain mixture of parents' genes
  1. Each gamete contains 23 chromosomes
    1. When fertilised, form cell with full number of chromosomes
2. Offspring inherits features from both parents - produces variation
Asexual reproduction
1. Only 1 parent
2. No fusion of gametes
3. No mixing of chromosomes/no genetic variation
4. Offspring are genetically identical (clones)
5. How plant & animals grow/produce replacement cells
6. Some organisms produce offspring using asexual reproduction (bacteria & certain plants)

Resource summary

	Created by Lilac Potato almost 10 years ago