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

Review….. Complete dominance Occurs when the phenotypes of the heterozygote (Hh) and dominant homozygote (HH) are identical Demonstrates (follows) “Mendelian Genetics” http://www.ucopenaccess.org/courses/APBiologyI/course%20files/multimedia/lesson19/lessonp.html

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 (Internediate) Dominance 1 allele is not completely dominant over the other, so the heterozygote (Hh) has intermediate (or mixed) phenotype between 2 alleles

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

“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)

Roan Animals Show Codominance

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

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

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

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-

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

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

Example of Epistasis Gene 1 Black =B Brown =b Gene 2 Color =C BC 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

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

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

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