Types of Inheritance

• Organisms that produce the same traits generations after generations reproduce by true breeding (homozygous)
• Selective breeding is crossing desirable traits from plants or animals to produce offspring with favorable characteristics (ex: farmers use selective breeding to produce crops that are brighter, tastier, and appealing)
• Inbreeding is the mating of closely related individuals for the purpose of maintaining certain characteristics (ex: royalty wanting to maintain royal blood
• Autosomal inheritance is the inheritance of genes found on the somatic chromosomes #1-22
• Autosomal dominant disorder: the disease-causing allele is dominant, so the affected individuals have genotypes AA or Aa
• Autosomal Recessive Disorder: The disorder-causing allele is recessive. Affected individuals have genotypes aa

  
  

  *if the parents are carriers for the disease (Aa), then the offspring will have that diease
• Incomplete dominance is when both alleles are equally dominant, causing a completely new phenotype that looks like a blend of the 2
• Codominance is when alleles are expressed equally at the same time
• Many traits in humans and other species are caused by the interactions of more than two alleles for one gene (multiple alleles)
• When there are multiple alleles for one characteristic the alleles have a dominance hierarchy, meaning some alleles are more dominant than others
• One single gene determines a person’s blood type
• Type A: I^A I^A or I^A i

  Type B: I^B I^B or I^B i

  Type AB: I^A I^B

  Type O: i i

  * the "i" allele is recessive to A and B, but A and B are codominant
• Sex-linked traits are traits controlled by genes located on sex chromosomes (X or Y)
• X and Y chromosomes act like homologous pairs in meiosis; however, they are not completely homologous (they only have a few genes in common)
• If the X linked trait is dominant then the affected males will pass the allele only to their daughters who will have a 100% chance of having that disorder

  Females with X linked dominant disorder can pass the allele to both sons and daughters, all of whom will have the disorder
• If the X linked trait is recessive, then the son would only need to inherit one allele to be affected, so if the mother has the trait, her sons have a 100% chance of getting the disorder

  A daughter would need to inherit both alleles to be affected (1 from mom and 1 from dad)

  * This makes X-linked recessive traits affect more males than females in a family!