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NON-MENDELIAN INHERITANCE PATTERNS (Modes of Inheritance)
H. BiologyMs. Kim
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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
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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
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“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
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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
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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
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“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
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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
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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
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• 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
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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
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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
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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
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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
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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