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  1. Inheritance patterns of single genes
    1. Recessive alleles often cause a reduction in the amount or function of the encoded protein
    2. Mutations that cause a loss of function in an essential gene result in a lethal phenotype
    3. Incomplete dominance occurs when two alleles produce an intermediate phenotype
    4. Some genes exist as three or more different alleles
    5. Alleles of the abo blood group can be dominant, recessive, or codominant
    6. Certain genes exhibit a gene dosage effect
    7. Overdominance occurs when heterozygotes have superior traits
    8. Dominant traits can skip a generation due to incomplete penetrance
    9. The expression of a trait can be influenced by the environment
    10. The outcome of certain traits can be influenced by the sex of the individual
  2. Gene interactions
    1. A cross involving a two-gene interaction can produce a 9:3:3:1 ratio in offspring when four distinct phenotypes are produced
    2. A cross involving a two-gene interaction can produce a 9:7 ratio when both genes are epistatic to each other
    3. Bridges observed an 8:4:3:1 ratio because the cream-eye allele can modify the eosin-eye allele, but not the red or white alleles







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