Transcript HMH 7.2 notes

7.2 Complex Patterns of Inheritance
KEY CONCEPT
Phenotype is affected by many different factors.
7.2 Complex Patterns of Inheritance
Phenotype can depend on interactions of alleles.
• In incomplete dominance, neither allele is completely dominant nor
completely recessive. Upper case letters with either subscripts or
superscripts are used to represent the different alleles.
– Heterozygous phenotype is intermediate between the two homozygous
phenotypes
– Homozygous parental phenotypes not seen in F1 offspring
Phenotype
Genotype
Phenotype
Genotype
Phenotype
Genotype
Green
B1B1
Steel blue
B2B2
Royal blue
B1B2
The royal blue betta fish is
heterozygous for the two
color alleles.
The green betta fish is
homozygous for the green
color allele.
The steel blue betta fish is
homozygous for the blue color
allele.
7.2 Complex Patterns of Inheritance
Other examples of incomplete dominance
How can you
tell that the
two color
alleles show
incomplete
dominance?
7.2 Complex Patterns of Inheritance
Other examples of incomplete dominance
7.2 Complex Patterns of Inheritance
• Codominant alleles will both be completely expressed.
– Codominant
alleles are
neither
dominant nor
recessive.
– The ABO blood
types result
from
codominant
alleles.
• Many genes have more than two alleles.
• APPLY How can two people with type B blood have a
child with type O blood?
7.2 Complex Patterns of Inheritance
Examples of Codominance
Synthesize:
How is
codominance
the same as
having no
dominant and
recessive
relationship at
all between
two alleles?
7.2 Complex Patterns of Inheritance
Another example of codominance compared to
incomplete dominance
Compare and Contrast:
How are codominant
alleles and incompletely
dominant alleles similar?
How are they different?
7.2 Complex Patterns of Inheritance
Many genes may interact to produce one trait.
• Polygenic traits are
produced by two or
more genes.
• At least 3 different genes
interact to produce the range
of human eye colors, such as
the examples on the right.
Order of dominance:
brown > green > blue.
7.2 Complex Patterns of Inheritance
Example of polygenic traits
Main Idea: Why might
polygenic traits vary
more in phenotype than
do single gene traits?
Contrast: How do
multiple-allele traits
differ from polygenic
traits?
7.2 Complex Patterns of Inheritance
• An epistatic gene can interfere with the expression other genes.
Fig. 2.4 Albinism
in mammals, such
as this hedgehog,
is caused by an
epistatic gene that
blocks the
production of
pigments. The
same epistatic
mechanism
applies to humans
and albinism.
They will have
very light skin,
hair, and eyes
regardless of the
other gene they
inherited.
7.2 Complex Patterns of Inheritance
The environment interacts with genotype.
• Phenotype is a combination
of genotype and
environment.
• The sex of sea turtles
depends on both genes
and the environment.
Warmer temps cause eggs
to develop into females and
cooler temps cause eggs to
develop into males.
•
7.2 Complex Patterns of Inheritance
Another example of environmental interactions with
genotype.
• Height is an example of a phenotype strongly affected by the
environment.
• Fingerprints are polygenic but
are also influenced by fetal
development. Ridge patterns
can be altered during weeks
6-13 of development, as the
fetus touches the wall of the
amniotic sac with its finger
pads
Connect: Sunlight can cause a
person’s hair to become lighter
in color. Is this an example of an
interaction between genes and
the environment? Why or why
not?