INCOMPLETE DOMINANCE, CODOMINANCE, MULTIPLE ALLELES, POLYGENIC TRAITS.
Incomplete Dominance Codominance
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Transcript of Incomplete Dominance Codominance
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