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Genetics. Incomplete Dominance. Where neither the dominant or recessive allele is truly dominant over the other, both are dominant. Incomplete Dominance. The heterozygote will “blend” the two traits into an intermediate third trait RED Flower x WHITE Flower ---> PINK Flower.

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incomplete dominance
Incomplete Dominance
  • Where neither the dominant or recessive allele is truly dominant over the other, both are dominant
incomplete dominance1
Incomplete Dominance
  • The heterozygote will “blend” the two traits into an intermediate third trait
  • RED Flower x WHITE Flower ---> PINK Flower
incomplete dominance2
Incomplete Dominance
  • Because neither allele is dominant over the other, we use a large base letter indicating the character and a capital superscript showing trait CR CRfor red flower

CW CWfor white flower

One allele from each parent is passed on. A cross would produce CR CW which is pink phenotype.


It’s important to know when you’re dealing with incomplete dominance

*notice that the offspring is showing 3rd phenotype

*notice that the trait in offspring is a blending of parental traits

  • Similar to incomplete dominance because it too creates a 3rd phenotype, different from parents.
  • Parental traits don’t blend, instead the two traits appear together in a hybrid





human blood types
Human Blood Types
  • Antigen- molecules that can trigger an immune response
  • A carries A antigen
  • B carries B antigen
  • AB has both antigens
  • O carries neither antigen

Rh Factor; Rh+ carry this antigen, while Rh- individuals don’t.

  • In transfusions, a new antigen cannot be introduced into the body of recipient





  • Who can give you blood?
  • People with TYPE O blood are called Universal Donors, because they can give blood to any blood type.
  • People with TYPE AB blood are called Universal Recipients, because they can receive any blood type.
  • Rh +  Can receive + or -
  • Rh -  Can only receive -

Universal Donor

Universal Recipient

polygenic inheritance
Polygenic Inheritance
  • When multiple genes affect a single character, variation
  • Height, weight, eye color, skin color
  • Suppose ABC were 3 “TALL” alleles and abc were 3 “short” alleles
  • Someone with genotype AABBCC would be very tall, while someone with genotype AaBBCC would be slightly less tall

AB: Dark Red plants

ab: white plants

Wide RANGE of phenotypes

environment influence on phenotype
Environment Influence on Phenotype
  • Sometimes an organisms phenotype depends on their environment regardless of genotype
  • For example, hydrangea flowers of the same genotype range from blue-violet to pink, depending on soil acidity
gene linkage
Gene Linkage
  • Genes on separate chromosomes assort and separate independently from each other
  • Genes located on SAME chromosome and close together (close gene-loci) tend to be inherited together. * Genetic linkage
  • If genes are far apart, but on the same chromosome, crossing over could separate them
sex linked genes
Sex-Linked Genes
  • Any gene located on an sex chromosome is a sex-linked gene
  • In humans, most of these are on the X chromosome (much bigger than Y)
red green color blindness
Red-green color blindness
  • X-linked color blind allele is recessive
  • Heterozygous females have normal vision
  • Males who get recessive allele in their only X chromosome are affected.

X-linked recessive disorders are more common in men than women

  • Women need 2 recessive alleles on each of her X chromosomes to be affected
  • Men only need 1 recessive allele on his only X chromosome to be affected