NON-MENDELIAN INHERITANCE PATTERNS (Modes of Inheritance)

H. BiologyMs. Kim

Review…..• What is Complete dominance?–Occurs when the phenotypes of the

heterozygote (Hh) and dominant homozygote (HH) are identical–Demonstrates (follows) “Mendelian Genetics”

– “Either” “Or”– EXAMPLE:• HH=Tall; Hh=Tall; hh=Tall• HH and Hh are both dominant and hh shows

recessive

Sometimes…

• Inheritance patterns do NOT follow the phenotype patterns (ex: 3:1) that Mendel saw in his pea plants• These patterns are called “Non-

Mendelian” Genetic Inheritance Patterns

“Non-Mendelian Genetics” Incomplete (Intermediate) Dominance• 1 allele is not completely dominant over the other,

so the heterozygote (Hh) has intermediate (or mixed) phenotype between 2 alleles

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What is Incomplete Dominance?• Incomplete Dominance – type of inheritance

when the heterozygous phenotype is a mixture of the two homozygous phenotypes– Example:• Green beta fish (CGCG)• Blue beta fish (CBCB)• Teal beta fish (CGCB)• CBCB x CGCG = teal beta fish

Neither allele is completely dominant or recessive

Figure 14.10

P Generation

F1 Generation

F2 Generation

RedCRCR

Gametes CR CW

WhiteCWCW

PinkCRCW

Sperm

CR

CR

CR

Cw

CR

CRGametes

1⁄2 1⁄2

1⁄2

1⁄2

1⁄2

Eggs1⁄2

CR CR CR CW

CW CWCR CW

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Incomplete Dominance Problem #1

If a red four o’clock flower is crossed with a pink four o’clock flower what will their offspring look like?

CRCR = red CWCW = white = pinkCRCW

Parent Genotypes CRCR x CRCW

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Perform cross

CR CR

• Genotype ratio:

• Phenotype ratio:

CRCR CRCR

CRCW CRCW

CR

CW

KEYCRCR = redCWCW= whiteCRCW = pink

2 CRCR : 2 CRCW

50% Red flowers & 50% Pink!

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Incomplete Dominance Problem #2

• In the four-o’clock plant, homozygous shows the red flower color and homozygous shows the white flower color. Cross a red plant with a white plant and list the genotypic and phenotypic ratios. CRCR x CW CW

4 CRCW and 100% pink

Let’s do some practice problems…

• Assume incomplete dominance…• A red gummy bear mates with a yellow gummy bear. Red (R) is

dominant. What are the genotype/phenotype ratios of their F1 offspring?

• 100% Rr 100% orange• If 2 F1 gummy bears from the question above mate. What are the

genotype/phenotype ratios of their F2 offspring?• 25% RR 50% Rr 25% rr• 25% Red 50% orange 25% yellow

“Non-Mendelian Genetics”

Codominance– “Co” means TOGETHER– 2 dominant alleles affect phenotype in

separate, distinguishable ways–BOTH phenotypes are present

• Ex’s of codominance– Speckled flower color– Roan animals (cattle & horses)

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What is Codominance?

• When both the dominant and recessive trait is expressed completely – Neither allele is dominant or recessive– Example: A flower that is homozygous for red flowers

(CRCR) is crossed with a plant that is homozygous for blue color (CB CB). The offspring (CR CB) will have spots of blue and spots of red but NO purple

– CR CR x CB CB = blue and red spotted CR CB

Roan Animals Show Codominance

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Codominance Example

• In cattle, fur color can either be red (CRCR), white (CWCW) or roan (CRCW).– Roan fur is both red hairs and white hairs together

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Codominance Example #1• Roan is a coat color found in some cows

– = red hair– = red and white hair (Roan) – = white hair

Cross a roan cow with a red cow

CRCR CRCW

CRCR CRCw

CR

Cw

CR

CR

Genotype ratio:Phenotype ratio:

Parents = CRCw x CRCR

2 CRCR : 2 CRCW

50% Roan, 50% Red

CRCR

CRCw

CwCw

Let’s do some practice problems…

• Assume codominance…• A blue flower mates with a yellow flower. Blue (B) is dominant.

What are the genotype/phenotype ratios of their F1 offspring? • 100% BY 100% Blue AND yellow flowers• If 2 F1 flowers from the question above mate. What are the

genotype/phenotype ratios of their F2 offspring?• 25% BB 50% BY 25% YY• 25% Blue 50% blue AND yellow 25% yellow

• Most genes can be found in more than 2 forms multiple alleles

• A type of inheritance pattern that involves:– 3+ alleles that influence gene’s phenotype– 4+ phenotypes can occur instead of only 3• Ex: Human Blood type

Multiple Alleles/Codominance

•There are 3 alleles (A,B,O) •We write the alleles:• A = IA

• B = IB

• O = i•When combined, they create 4 blood phenotypes: A, B, AB, O

The ABO blood group in humansIs determined by multiple alleles

(similar to codominance)

Table 14.2

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Blood Type Key

• A Blood Type – Homozygous Type A IAIA

– Heterozygous Type A IAi

• B Blood Type– Homozygous Type B IBIB

– Heterozygous Type B IBi

• AB Blood Type (codominant) IAIB

– AB is the universal receiver

• O Blood Type (recessive) ii – O – is the universal donor

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Blood Type

Blood Types of Parents All possible genotypes of parents All possible genotypes of

childrenAll possible blood types (phenotypes) of children

A & O IAIA, IAi, ii IAi, ii A,O

B & O

A & B IAIA, IAi, IBIB, IBi IAIB, IAi, IBi, ii

AB & A IAIA, IAIB, IAi, IBi AB, A, or B

AB & B IAIB, IBIB, IBi

AB & O IAIB, ii IAi, IBi A or B

O & O ii ii O

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Blood Type Answers

Blood Types of Parents All possible genotypes of parents All possible genotypes of

childrenAll possible blood types (phenotypes) of children

A & O IAIA, IAi, ii IAi, ii A,O

B & O IBIB, IBi, ii IBi, ii B,O

A & B IAIA, IAi, IBIB, IBi IAIB, IAi, IBi, ii AB, A, B or O

AB & A IAIB, IAIA, IAi IAIA, IAIB, IAi, IBi AB, A, or B

AB & B IAIB, IBIB, IBi IAIB, IAi, IBIB, IBi AB, A, or B

AB & O IAIB, ii IAi, IBi A or B

O & O ii ii O

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Example Problem• A type AB woman marries a type O man.

What are the possible genotypes of their offspring?

Phenotype AB x OGenotype IAIB x ii

IA

IB

i

i

IAi IBi

IAi IBi

Genotype Ratio: 2 IAi: 2 IBi

Phenotype Ratio: 50% A Blood Type 50% B Blood Type

Blood Type Practice

• What are the possible blood types of a child who's parents are both heterozygous for "B" blood type? – IBi X IBi – 50% chance IBi, 25% chance IBIB, 25% chance ii

• 75% chance of B type and 25% chance of O type

• What are the chances of a woman with Type AB and a man with Type A having a child with Type O?– IA? x IAIB – 0% chance of Type O b/c mom can’t donate “i” allele

• Jill is blood Type O. She has two older brothers with blood types A & B. What are the genotypes of her parents? – IAi and IBi

Polygenic Inheritance

• 2 or more genes affect 1 phenotype– “Poly” also means many – “Genic” has to do with

genes– Traits that can have a wide

range of color• Ex:

• Height, skin color, eye color

AaBbCc AaBbCc

aabbcc Aabbcc AaBbcc AaBbCc AABbCc AABBCc AABBCC

20⁄64

15⁄64

6⁄64

1⁄64

Frac

tion

of p

roge

n y

Figure 14.12

SKIN COLOR:6 genes involved

Nature and Nurture: The Environmental Impact on Phenotype

• Another departure from simple Mendelian genetics the phenotype depends on environment as well as on genotype• Called multifactorial inheritance –Ex: identical twins looking different hydrangea flowers