2/1/2012 Genetics

Click HERE for audio.


Incomplete Dominance

-Two alleles produce intermediate results; heterozygotes have intermediate phenotype

-50% of the normal protein is not sufficient to produce the same phenotype as a homozygote




Multiple alleles vs. single pair alleles

C=full coat

Cch=chinchilla pattern (allele produces partial defect)

Ch=himalayan pattern (temp sensitive; extremities only)

c= albino (defective allele that cannot produce pigments)


C dominate to cch, ch, and c

cch recessive to C but dominant to c and ch

ch is recessive to C and cch but dominate to c

c is recessive to C, Cch and Ch


Other examples of multiple allele

-Siamese cats (Himalayan pattern)

  • Brown Swiss Cattle (opposite of himalayan pattern)


Alleles of ABO blood group

-Can be dominant, recessive, or codominant

  • ii= type O blood
  • IAIA or IAi = type A blood
  • IBIB or IBi = Type B Blood
  • IAIB = type AB blood (codominant)
  • Codominance: a phenomenon in which two alleles are both expressed in the heterozygous individual


Incomplete Dominance vs Codominance

-In incomplete dominance a blending of the two alleles produces a third phenotype (white x red = pink)

-Codominance is the equal expression of both alleles (white x red = white spotted) ex. AB blood type equal expression of both alleles


Overdominance (heterozygous advantage)

-Due to two alleles that produce proteins with slightly different amino acid sequence

-Allows individual to function under broader range of environmental conditions (more adaptable)

-Less susceptible to specific pathogens/disease (more difficult to recognize and compete)


Hybrid Vigor (heterosis)

-Different from overdominance because of the involvement of many genes

-Hybrids display traits (size, weight, growth rate, disease resistance) that are superior to parental strains

-Intraspecific (within a species) crossing of sub-species, varieties, breeds, stains, or populations.


Interspecific (between species)




Interspecific hybrids usually sterile. Why?


Incomplete Penetrance

-Phenomenon in which a dominate allele does not always “penetrate” into the phenotype of the individual

-Described at the POPULATION level (ex 60% penetrant trait = 60% of heterozygotes express this phenotype)

-Individual either has the trait or does not have the trait

-Expression of dominant trait may skip generations


Example of Incomplete Penetance & Variable Expressivity

-An allele may not be expressed to the same degree in all individuals: Polydactyly


Environmentally influenced traits; Expression influenced by Environment

-Remember the Himalayan pattern? (temperature influenced)

-Hydrangea, blue or pink? Expression of pigment color influenced by pH of soil


Sex influence inheritance

-Allele can be dominant in one sex and recessive in the opposite sex

-Baldness: autosomal trait (not X-linked)


Males Females

BB Bald Bald

Bb Bald Nonbald

bb nonbald nonbald


Sex limited traits

-Trait occurring in only one of the sexes (ex breast development, beard growth, bright plumage in birds, etc).

-Difference between sex limited or sex-influence vs X-linked inheritance is where the gene is located (autosomal vs sex chromosome)

Posted on February 1, 2012, in Genetics. Bookmark the permalink. Leave a comment.

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s

%d bloggers like this: