Concept 11.3: Inheritance patterns are often more complex than
predicted by simple Mendelian genetics Not all heritable characters
are determined as simply as the traits Mendel studied. However, the
basic principles of segregation and independent assortment apply
even to more complex patterns of inheritance.
Slide 3
Complete Dominance: Homozygous and heterozygous phenotypes are
indistinguishable. These look the same
Slide 4
Dominant alleles are not necessarily more common in populations
than recessive alleles. Six finger trait is dominant to the five
finger trait
Slide 5
Extending Mendelian Genetics for a Single Gene Inheritance of
characters by a single gene may deviate from simple Mendelian
patterns in the following situations. When alleles are not
completely dominant or recessive. When a gene has more than two
alleles. When a single gene influences multiple phenotypes.
Slide 6
In incomplete dominance, the phenotype of F 1 hybrids is
somewhere between the phenotypes of the two parental
varieties.
Slide 7
In codominance, two dominant alleles affect the phenotype in
separate, distinguishable ways x Homozygous White Homozygous Black
Heterozygous Black & White
Slide 8
Carbohydrate (b) Blood group genotypes and phenotypes Allele
Red blood cell appearance Genotype none B A IBIB Phenotype (blood
group) i IAIA IAIBIAIB ii I A I A or I A i I B I B or I B i B A O
AB (a) The three alleles for the ABO blood groups and their
carbohydrates Recessive
Slide 9
Pleiotropy: The property of a gene that causes it to have
multiple phenotypic effects. Example: Sickle cell anemia is caused
by one gene but has the following phenotypic effects: Anemia
Episodes of pain Swollen hands and feet Frequent infections Delayed
growth
Slide 10
BE Be BE be BBEE bbee BbEE BbEe bEbe bE Be BBEe BbEEbbEE bbEe
BbEe BBEeBbEeBbeeBBee BbEebbEe Bbee 9 : 4 : 3 Eggs Sperm BbEe
Epistasis: a gene at one locus alters the phenotypic expression of
a gene at a second locus.
Slide 11
Polygenic Inheritance Quantitative characters are those that
vary in the population along a continuum. Quantitative variation
usually indicates polygenic inheritance, an additive effect of two
or more genes on a single phenotype. Skin color in humans is an
example of polygenic inheritance.
Nature and Nurture: The Environmental Impact on Phenotype
Another departure from Mendelian genetics arises when the phenotype
for a character depends on environment as well as genotype.
Slide 14
Integrating a Mendelian View of Heredity and Variation An
organisms phenotype includes its physical appearance, internal
anatomy, physiology, and behavior. An organisms phenotype reflects
its overall genotype and unique environmental history.
