Incomplete Dominance Codominance In a nutshell!. Review: Dominant/Recessive One allele is dominant over the other (capable of masking the recessive allele)

Incomplete DominanceCodominance

In a nutshell!

Review: Dominant/Recessive

• One allele is dominant over the other (capable of masking the recessive allele)

PP = purple pp = white Pp = purple

Review Problem: Dominant/Recessive

• In pea plants, purple flowers (P) are dominant over white flowers (p) show the cross between two heterozygous plants.

P

p

P p

pp

Pp

Pp

PP- PP (1); Pp (2); pp (1)- ratio 1:2:1

- purple (3); white (1)- ratio 3:1

GENOTYPES:

PHENOTYPES:

• Snapdragons

http://faculty.pnc.edu/pwilkin/incompdominance.jpg

http://www.dobermann-review.com/info/genetics/mendels_genetic_laws/Gregor%20Mendel.jpg

HUH?

Incomplete Dominance

X

R1

R2

F1

F2R2R2 does not produce pigment

Heterozygote only produces ½ pigment of R1R1

http://www.google.ca/images?hl=en&q=incoplete%20dominance&rlz=1W1SNNT_enCA397&um=1&ie=UTF-8&source=og&sa=N&tab=wi&biw=1345&bih=555

http://2.bp.blogspot.com/_uPFMFfHgGGg/SygBEtl5D1I/AAAAAAAAAKc/nylZiiL2k7s/s320/incomplete+dominance.jpg

Incomplete Dominance• A third (new) phenotype appears in the

heterozygous condition.• Neither trait is completely dominant over the other,

so a heterozygous plant is a mix.

RR = red rr = white Rr = pink

Problem: Incomplete Dominance

• Show the cross between a pink and a white flower.

- Rr (2); rr (2)- ratio 1:1

- pink (2); white (2)- ratio 1:1

R r

r

r

rrRr

rrRr

GENOTYPES:

PHENOTYPES:

Codominance

• The heterozygous condition, both alleles are expressed equally

• Lots of times, fur color in animals is this way. (think spotted or 2 colors)

CODOMINANCE

• The condition in which both alleles in a heterozygous organism are expressed. (Both are dominant together)

• BOTH alleles contribute to the phenotype.

• The two alleles don’t blend, but are rather both present in the offspring.

http://search.vadlo.com/b/q?rel=2&keys=Dominance+Incomplete+Dominance+Codominance+PPT

Roan Horse

Roan Cattle

Variegated Clover

http://3.bp.blogspot.com/_zUPrgMM5tUg/SSVdrs59_uI/AAAAAAAAAA8/qJGjG2nZPhk/s200/codominance.GIF

http://www.ccs.k12.in.us/chsteachers/BYost/Biology%20Notes/CH11notescoincompletedom_files/image004.jpg