Inheritance

• A genotype is the genetic makeup of an organism.
• A phenotype is the physical expression of a gene and its interaction with the environment
• an allele is a different version of a gene that codes for a different amino acid
• alleles can be dominant (D), recessive (r) or codominant
• monohybrid inheritance is from one allele
• location on a chromosome is the locus
• human cells are diploid, meaning they have 2 copies of each chromosome
• reasons expected ≠ observed

  1. random fertilisation
  2. small population sample
  3. codominance
  4. sex linkage
  5. epistasis
• reasons meiosis produces genetic variation in gametes

  1. chromatids crossing
  2. independent assortment of chromosomes
• dihybrid inheritance is from 2 different genes/alleles
• more than 2 alleles can lead to multiple allele crosses
• homozygous is 2 of the same alleles
• heterozygous is 2 different alleles
• if X linked genetic disease gene is inherited:

  XX: carriers or affected

  XY: affected
• autosomal genes are on non sex chromosomes
• epistasis is when one allele masks or suppresses the expression of another allele
• if the calculated chi squared value is less than the critical value, the null hypothesis is accepted
• Ratio of heterozygous pairs in dihybrid crosses is 9:3:3:1