NON-MENDELIAN INHERITANCE PATTERNS (Modes of Inheritance) H. Biology Ms. Kim
Feb 22, 2016
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
rog e
ny
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