1. NON-MENDELIAN INHERITANCE PATTERNS AP Biology Ms. Gaynor
Chapter 14 (Part 4)
NON-MENDELIAN INHERITANCE PATTERNS
AP Biology
Ms. Gaynor

2. Review….. Complete dominance
Occurs when the phenotypes of the heterozygote (Hh) and dominant homozygote (HH) are identical
Demonstrates (follows) “Mendelian Genetics”

3. 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

4. “Non-Mendelian Genetics”
Incomplete (Internediate) Dominance
1 allele is not completely dominant over the other, so the heterozygote (Hh) has intermediate (or mixed) phenotype between 2 alleles

5. Figure 14.10  1⁄2 P Generation F1 Generation F2 Generation Red CRCR
Gametes CR CW 
White
CWCW
Pink
CRCW
Sperm Cw
1⁄2
Eggs
CR CR
CR CW
CW CW
Figure 14.10

6. “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)

7. Roan Animals Show Codominance

8. The Relation Between Dominance and Phenotype
Dominant and recessive alleles
Do not really “interact”
Actually variations in nucleotide sequence in DNA
Lead to synthesis of different proteins that produce a phenotype
Ex: Dominant  ATTACGGCCATC
Recessive  ATTCGGGCCATC

9. 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

10. Table 14.2
The ABO blood group in humans Is determined by multiple alleles (similar to codominance)

12. Blood Types- Positive and Negative
+ and – in blood type is determined by an DIFFERENT cell membrane protein (tag) attached to the RBC
Follows a COMPLETE DOMINANCE inheritance pattern
Rh+ = positive allele
Rh+/Rh+ or Rh+/Rh-
Rh- = negative allele
Rh-/Rh-

13. Additional Inheritance Patterns…oh my!
In pleiotropy
1 gene has multiple phenotypic effects
“Pleios” in Greek means “many”
A single gene can affect several characteristics
Ex: sickle cell anemia and cystic fibrosis

14. Additional Inheritance Patterns…oh my!
In epistasis
A gene at one locus (location) alters the phenotypic expression of a gene at a second locus

15. Example of Epistasis Gene 1 Black =B Brown =b Gene 2 Color =CBC bC Bc bc
1⁄4
BBCc
BbCc
BBcc
Bbcc
bbcc
bbCc
BbCC
bbCC
BBCC
9⁄16
3⁄16
4⁄16 
Sperm
Eggs
Example
of Epistasis
Gene 1
Black =B
Brown =b
Gene 2
Color =C
No color =c

16. Polygenic Inheritance
2 or more genes affect 1 phenotype
“Poly” also means many
“Genic” has to do with genes
Opposite of pleiotropy
Ex:
Height, skin color, eye color, IQ, body build

17. SKIN COLOR: 6 genes involved
AaBbCc
aabbcc
Aabbcc
AaBbcc
AABbCc
AABBCc
AABBCC
20⁄64
15⁄64
6⁄64
1⁄64
Fraction of progeny
SKIN COLOR:
6 genes involved
Figure 14.12

18. 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: human fingerprints
hydrangea flowers