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