6.1.2. Patterns of inheritance

• how is genetic variation achieved during meiosis?

  • prophase 1; crossing over of non-sister chromatids
  • metaphase 1; independent assortment of homologous chromosomes
  • metaphase 2; independent assortment of chromatids
  • anaphase 2; independent segregation of chromatids
• hardy weinberg principal valid if

  • population is large
  • mating is random
  • organisms are diploid and reproduce by sexual reproduction only
  • no overlap between generations
  • allele frequency constant
  • mating is isolated and no migration occurs
  • allele frequencies equal in both sexes
  • no selection pressures so no evolution
  • no mutations arise
• p+q = 1 where p is dominant allele and q is the recessive

  P^2 + 2pq + q^2 = 1 where P^2 is the homozygous dominant genotype, 2pq is the heterozygous genotype and q^2 is the homozygous recessive
• how does equal reproduction lead to genetic variation?

  • genetic variation down to the variety of alleles and offspring have them from more than one parent
  • random fertilisation paired with meiosis producing genetically unique gametes
  • crossing over can occur in prophase 1 where alleles swapped with non-sister chromatids so the base sequence of chromosomes are altered
  • independent assortment occur in metaphase 1 and relevant in metaphase 2 if crossing over has occurred
• epistasis occurs when one allele codes for a repress or protein tha binds to the promoter of the second allele, stopping the transcription and translation of it and protein synthesis doesn’t occur. the product inhibits the enzyme
• autosomal linkage is a reason for mendalian ratios not matching as this means both alleles occur on the same chromatid and there is no independent assortment and alleles inherited together end up on the same gamete unless crossing over occurs and chaisma forms between loci