Bio B5

• mitosis

  • asexual reproduction
  • results in the formation of two identical daughter cells
• meiosis

  • sexual reproduction
  • results in the formation of four genetically non-identical daughter cells
• sexual reproduction

  • the fusion of male and female gametes
  • cells in reproductive organs divide by meiosis to create gametes
  • gametes contain half of the number of chromosomes found in all body cells
• cells split

  • each cell has a pair of each chromosome (diploid cell)
  • during meiosis each pair of chromosomes replicate and the cell splits in two
• further cell splitting

  • after initially splitting there are now two identical cells
  • the diploid cell divides again
• haploid cells

  • this creates four genetically different gametes that each have half the number of chromosomes of the parent cell
  • cells that only have one copy of each chromosome are called haploid cells
• gametes fertilise

  • during sexual reproduction, the male gamete fertilises the female gamete
  • the fertilised cell now has the normal number of chromosomes
• mitosis

  • once the gametes have combined, the new cell divides by mitosis (the cells grow asexually)
  • as soon as the embryo reaches a certain size, cells begin to differentiate
• genome

  • the entire genetic material of an organism
  • lots of levels of organisation
• dna

  • double helix polymer
  • made up of two strands
• genes

  • a small section of dna which codes for protein
• chromosomes

  • long strands of dna are coiled to form chromosomes
  • chromosomes contain many genes
  • human body cells contain 23 pairs of chromosomes, one of each pair coming from each parent
• alleles

  • different forms of the same gene
  • humans have pairs of each gene and in one gene, each half of the may have different alleles
  • people's characteristics are determined by the alleles they have
  • alleles can either be dominant or recessive
• dominant alleles

  • always expressed, regardless of the other allele
• recessive allele

  • also expressed if the other allele is also recessive (bb)
• genotype

  • combination of alleles an organism has
  • if two alleles are different, we say that person is heterozygous
  • if two alleles are the same, we say that person is homozygous
• phenotype

  • observed characteristic of a person
  • determined by the interaction between genotype and the environment
• mutation

  • permanent change in the nucleotide sequence of dna
  • mutations happen continuously and normally only slightly affect proteins or don't affect them at all
  • a mutation may change the structure or shape of a protein
• undesirable change

  • the outcome of a mutation is almost detrimental to protein function
• survival advantage

  • rarely, a mutation will give a survival advantage
  • such as a resistance to an antibiotic in bacteria
  • these mutations can be beneficial and represent the foundation of evolution
• variation

  • within a population, variation describes differences in the characteristics of individuals