7.2 Complex Patterns of Inheritance
KEY CONCEPT
Phenotype is affected by many different factors.
7.2 Complex Patterns of Inheritance
In (3.)incomplete dominance, (AKA- intermediate
dominance) neither allele is completely dominant nor
completely recessive.
Heterozygous phenotype is intermediate between
the two homozygous phenotypes
Use capital letters and apostrophes’
RR-red
homozygous dominant
RR’-pink heterozygote is intermediate
R’R’-white
homozygous recessive
7.2 Complex Patterns of Inheritance
7.2 Complex Patterns of Inheritance
7.2 Complex Patterns of Inheritance
Phenotype can depend on interactions of alleles.
• In (3.)incomplete dominance, neither allele is
completely dominant nor completely recessive.
– Heterozygous phenotype is intermediate between
the two homozygous phenotypes
– Homozygous parental phenotypes not seen in F1
offspring
–B1B1 Green B2B2 blue
B1B2 royal blue
7.2 Complex Patterns of Inheritance
• (4)Codominant –equal expression of both alleles.
– Codominant alleles are neither dominant nor
recessive.
Ex. The ABO blood types result from
codominant alleles.
Ex. Sickle cell disorder
RR- normal red blood cell shape
RS-sickle cell trait- carrier
SS-sickle cell anemia
7.2 Complex Patterns of Inheritance
• Genetic disorder• Hemoglobin- a protein in Red Blood Cells that carry
oxygen to body cells
• Sickle cell anemia-a genetic disorder that causes a
change in the shape of red blood cells
• Sickle cell Trait-some normal, some sickle shaped cells
7.2 Complex Patterns of Inheritance
7.2 Complex Patterns of Inheritance
(5) multiple alleles
• Traits that are controlled by more than 2 alleles, although
only two alleles exist in a diploid cell.
• Example- Human Blood Types-each person inherits two
alleles, one from each parent, but three exist in the
human “gene pool”.
4 blood types
3 alleles
• Type-A
I AI A, I Ai
A is dom. to O
• Type-B
I BI B, I Bi
B is dom. To O
• Type-AB IAIB
AB are codominant
• Type-O
ii
recessive
• This is determined by the shape of proteins on red blood
cells and by the presence or absence of plasma
antigens. O universal donor-AB universal receiver.
7.2 Complex Patterns of Inheritance
(6)Polygenic -many genes may interact to produce one
trait. The genes may be on the same or on a different
chromosome.
Result in a wide range
of variation.
Ex. Hair color, height
eye color
Order of dominance:
brown > green > blue.
7.2 Complex Patterns of Inheritance
Often compared to a bell curve
• AA,BB,CC
• aa.bb.cc
• Aa,Bb,Cc
highest range
lowest range
middle
7.2 Complex Patterns of Inheritance
• An (7)epistatic gene can interfere with other genes.
7.2 Complex Patterns of Inheritance
Other factors of gene expression Phenotype is a
combination of genotype and environment.
•External environmenttemperature, nutrition,
light
•Internal factors: different
hormones, structures, and
effects of aging.
Ex.The sex of sea turtles
depends on both genes
and the environment(temperature of the nest)
•Ex.Height is an example of a
phenotype strongly affected
by the environment.