Non-Mendelian Genetics (bio test 6)

Incomplete dominance

• The “blending” of two alleles

• i.e. red (RR) + white (rr) → pink (Rr)

Codominance

• Both alleles show up fully in the phenotype

• Patterns like black and white spots

• RR + WW → RW

Sex-linked traits

• What: a gene located on either sex chromosome

• The X chromosome carries many X-linked genes that control traits unrelated to sex

  • i.e. colorblindness

• Most X-linked disorders are more common in males because these are due to recessive alleles

  • A male receiving a single X-linked accessible allele from his mother will have the disorder

  • A female must receive the allele from each parent to be affected

Multiple alleles

• ABO blood type group phenotype is controlled by three alleles that produce four phenotypes

• IA and IB are codominant: both alleles are expressed in heterozygous individuals who have an AB blood type

Lethal traits

• Survival of offspring affect offspring ratios

• Lethality can be recessive or dominant, but dominant weasel alleles are rare because they are quickly eliminated from the population

Polygenetic traits

• Single phenotypic character is due to the additive effects of 2 or more genes; example is human skin color

• There are over 170 genes involved in melanin production