Non-Mendelian Genetics
Mendelian Genetics: Dominant & Recessive Review
One allele is DOMINANT over the other (because the dominant allele can “mask” the recessive allele)
genotype: PPphenotype: purple
genotype: ppphenotype: white
genotype: Ppphenotype: 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 (25%) Pp (50%) pp (25%)- ratio 1:2:1
- purple (75%) white (25%)- ratio 3:1
GENOTYPES:
PHENOTYPES:
Non-Mendelian Genetics
Incomplete DominanceCodominanceMultiple AllelesPolygenic TraitsSex-Linked Traits
Incomplete Dominancea third (new) phenotype
appears in the heterozygous condition as a BLEND of the dominant and recessivephenotypes. Ex - Dominant Red (R) + Recessive White (r) = Hybrid Pink (Rr)
RR = red rr = white Rr = pink
Problem: Incomplete Dominance
Show the cross between a pink and a white flower.
- RR (0%) Rr (50%) rr (50%)- ratio 1:1
- pink (50%); white (50%)- ratio 1:1
R r
r
r
rrRr
rrRr
GENOTYPES:
PHENOTYPES:
Codominancein the heterozygous condition, both alleles are expressed equally with NO blending!
Represented by using two DIFFERENT capital letters. Example: Dominant Black (B) + Dominant White (W) = Speckled Black and White
Phenotype (BW)
Sickle Cell Anemia -
NN = normal cells
SS = sickle cells NS = some of each
Codominance Example: Speckled Chickens
BB = black feathersWW = white feathersBW = black & white speckled feathers
Notice – NO GRAY!
NO BLEND!
Each feather is
either black or white
Codominance Example: Rhodedendron
R = allele for red flowersW = allele for white flowersCross a homozygous red flower
with a homozygous white flower.
Codominance Example:Roan cattle
cattle can be red (RR – all red hairs) white (WW – all white hairs) roan (RW – red and white hairs together)
Codominance Example:Appaloosa horses
Gray horses (GG) are codominant to white horses (WW). The heterozygous horse (GW) is an Appaloosa (a white horse with gray spots).
Cross a white horse with an appaloosa horse.
W W
G
W
GWGW
WWWW
Problem: Codominance
Show the cross between an individual with sickle-cell anemia and another who is a carrier but not sick.
N S
S
S
NS
NS
SS
SS
- NS (50%) SS (50%)- ratio 1:1
- carrier (50%) sick (50%)- ratio 1:1
GENOTYPES:
PHENOTYPES:
Multiple Allelesthere are more than two alleles for a gene.
Ex – blood type consists of two dominant and one recessive allele
options. Allele A
and B are
dominant over
Allele O (i)
Multiple Alleles:Lab Mouse Fur Colors
Fur colors (determined by 4 alleles): black agouti yellow
Multiple Alleles:Rabbit Fur Colors
Fur colors (determined by 4 alleles): full, chinchilla, himalayan, albino
Multiple Alleles:Blood Types (A, B, AB, O)
Rules for Blood Types: A and B are co-dominant (Both show)
AA or IAIA = type A BB or IBIB = type BAB or IAIB = type AB
A and B are dominant over O (Regular dom/rec)AO or IAi = type ABO or IBi = type BOO or ii = type O
Multiple Alleles:Blood Types (A, B, AB, O)
PhenotypePossible
Genotype(s)
Allele (antigen) on RBC surface
Can Donate Blood
To
Can Receive Blood From
AIAi
IAIA A A, AB A, O
BIBi
IBIB B B, AB B, O
AB IAIB AB ABA, B,
AB, O
O ii OA, B,
AB, O O
Problem: Multiple Alleles
Show the cross between a mother who has type O blood and a father who has type AB blood.
- Ai (50%) Bi (50%)- ratio 1:1
- type A (50%) type B (50%)- ratio 1:1
GENOTYPES:
PHENOTYPES:
i i
A
B
Ai
Bi
Ai
Bi
Problem: Multiple Alleles
Show the cross between a mother who is heterozygous for type B blood and a father who is heterozygous for type A blood.
-AB (25%); Bi (25%); Ai (25%); ii (25%)- ratio 1:1:1:1
-type AB (25%); type B (25%) type A (25%); type O (25%)- ratio 1:1:1:1
GENOTYPES:
PHENOTYPES:
A i
B
i
AB
ii
Bi
Ai
Polygenic Traitstraits produced by multiple genesexample: skin color
Sex-Linked TraitsGene is attached to
the X chromosome only, not found on the Y chromosome at all. (women have XX, men have XY chromosomes). These disorders are more common in boys.
examples: red-green colorblindness
Sex-Linked Traitsin males, there is
no second X chromosome to “mask” a recessive gene. If they get an X with the disorder, they have it. Girls must inherit defective X’s from both parents.
Sex-Linked TraitsA: 29, B: 45, C: --, D: 26 Normal vision
A: 70, B: --, C: 5, D: -- Red-green color blind
A: 70, B: --, C: 5, D: 6 Red color blind
A: 70, B: --, C: 5, D: 2 Green color blind