DNA and Chromsomes

• Chromosome structure:

  • When they first become visible, chromosomes appear as two threads. Each thread is called a chromatid
  • The DNA in chromosomes is held by histone protiens
  • The DNA-histone complex is coiled then condensed into a chromosomes
  • The number of chromosomes is consistent across a species
• Homologous chromosomes:

  • the egg and sperm each hold half the chromosomes, when combined they make the full set
  • the total number of chromosomes is called the diploid number - in humans this is 46
• Alleles:

  • alternate forms of the same gene
  • each individual inherits one allele from each parent. They may be the same or different
  • when they are different each allele has a different base sequence therefore a different amino acid sequence