Non-Mendelian Genetics

Mendelian Genetics:

Dominant & Recessive ReviewOne 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 & RecessiveIn 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 Dominance

Codominance

Multiple Alleles

Polygenic Traits

Sex-Linked Traits

Incomplete Dominance

a third (new) phenotype

appears in the heterozygous

condition as a BLEND of the

dominant and recessive

phenotypes. Ex - Dominant Red (R) + Recessive White

(r) = Hybrid Pink (Rr)

RR = red rr = white Rr = pink

Problem:

Incomplete DominanceShow 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 ChickensBB = black feathers

WW = white feathers

BW = black & white speckled feathers

Notice –

NO GRAY!

NO BLEND!

Each feather is

either black or white

Codominance Example:

RhodedendronR = allele for red flowers

W = allele for white flowers

Cross 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 horsesGray 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:

CodominanceShow 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 Alleles

there 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 B

AB or IAIB = type AB

A and B are dominant over O

AO or IAio = type A

BO or IBio = type B

OO or ioio = type O

Multiple Alleles:

Blood Types (A, B, AB, O)

Phenotype

Possible

Genotype(s)

Allele

(antigen)

on RBC

surface

Can

Donate

Blood

To

Can

Receive

Blood

From

A

IAio

IAIA A A, AB A, O

B

IBio

IBIB B B, AB B, O

AB IAIB AB AB

A, B,

AB, O

O ioio O

A, B,

AB, O O

Problem:

Multiple AllelesShow 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 o io

IA

IB

IAio

IBio

IAio

IBio

Problem:

Multiple AllelesShow 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:

Polygenic Traits

traits produced by multiple genes

example: 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 Traits

in 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