Monohybrid Inheritance

• Genotype: genetic makeup of an organism in terms of the alleles present (e.g. Tt or GG)
• Phenotype: physical or other features of an organism due to both its genotype and its environment (e.g. tall plant or green seed)
• genotype + environment + random variation → phenotype
• Homozygous: having two identical alleles of a particular gene (e.g. TT or gg). Two identical homozygous individuals that breed together will be pure-breeding
• Heterozygous: having two different alleles of a particular gene (e.g. Tt or Gg), not pure-breeding
• Dominant: an allele that is expressed if it is present (e.g. T or G)
• Recessive: an allele that is only expressed when there is no dominant allele of the gene present (e.g. t or g)
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  Pedigree

  
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  Genetic

  
• Co-dominance: when neither of two alleles is dominant to each other.
• There are three alleles for blood group given by the symbols $I^A$ , $I^B$ and $I^O$ .
• $I^A$ and $I^B$ are co-dominant giving blood group AB or $I^AI^B$ , and both dominant to $I^O$ .
• Sex-linked characteristic: a characteristic in which the gene responsible is located on a sex chromosome and that this makes it more common in one sex than in the other
• Colour blindness as an example of sex linkage