Understanding Inheritance

1
Understanding Inheritance

• Chapter 5 Lesson 2
• Part 2

2
Modeling Inheritance
A Punnett square is a model used to predict
possible genotypes and phenotypes of offspring.
3
Modeling Inheritance
A pedigree shows phenotypes of genetically
related family members.
4
Variations in Mendel's Theories

• Incomplete dominance
• Codominance
• Polygenic inheritance
• Sex-Linked traits

5
Variations in Mendel's Theories

• Sometimes traits appear to be blends of alleles.
• Alleles show incomplete dominance when the
  offsprings phenotype is a blend of the parents
  phenotypes.
• Codominance occurs when both alleles can be
  observed in a phenotype.

6
Incomplete dominance
a type of inheritance in which the alleles
expressing a particular characteristic are
neither dominant or recessive two traits combine
or blend together to produce a different trait (a
blend of two traits) (when offspring of two
homozygous parents show an intermediate phenotype)
7
Incomplete dominance
example flower color in snapdragons four
oclock flowers
8
Codominance

• In codominance both traits are expressed there
  are no dominant and recessive
• traits
• Example
• roan cattle

9
Codominance
In incomplete dominance neither allele is fully
dominant. This is different from codominance, in
which both alleles are fully expressed, resulting
in organisms that display the characteristics of
both parents.
10
Codominance
In codominance, both alleles are expressed
independently and are uniquely recognizable.
11
Codominance
Some traits, such as human ABO blood type, are
determined by more than one allele.
12
Polygenic Inheritance

• two or more genes producing a single trait
• occurs when multiple genes determine the
  phenotype of a trait
• (examples in humans hair color, skin color, eye
  color, height, intelligence, body build, etc.)

13
Genes and the Environment

• An organisms environment can affect its
  phenotype.
• Some examples of environmental factors that
  affect phenotype are soil type that a flower is
  growing in or time of year that a butterfly
  develops.

14
Genes and the Environment Example Hydrangea
For most French hydrangeas (Hydrangea
macrophylla), the flower color indicates the pH
of the soil. In strongly acid soil (pH below 6),
flowers turn blue. In alkaline soil (pH above 7),
flowers turn pink or even red. In slightly acid
or neutral soil (pH 6 to 7), blooms may be purple
or a mix of blue and pink on a single shrub