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Mr. Altorfer
Science
Traits and Inheritance
Pages 120 to 125
Traits and Inheritance
• Genes: One set of instructions for an
inherited trait.
– Each parent gives one set of genes to
their offspring.
– Each offspring then has two forms of the
same gene for every characteristic
– Tall plants genes could be TT, Tt or tt.
Traits and Inheritance
• Alleles- The different forms of a gene.
– Dominant alleles are shown with a
capital letter.
– Recessive alleles are shown with a lower
case letter.
– Remember TT, Tt or tt?
Alleles
Phenotype
• Phenotype- The appearance of an
organism.
– Example: What do these organisms look
like?
Genotype
• Genotype- The gene makeup of an
organism.
– Example: Remember the tall gene?
• TT, Tt, tt
– All three of these combinations are a
different genotype
Genotype
• Homozygous- When an organism has
two dominant or recessive alleles.
– Example: TT or tt (Pure Bred)
• Heterozygous- When an organism has a
mixture of dominant and recessive alleles.
– Example: Tt (Hybrid)
Punnett Square
• Punnett Square- A tool used to
organize all the possible combinations
of offspring from a set of parents.
Punnett Square
As a result of this
cross, what color will
the offspring of these
two birds be?
What is the
phenotype of each of
the offspring?
What is the genotype
of each of the
offspring?
Incomplete Dominance
• Incomplete Dominance- Occurs when
one trait is not completely dominant
over another trait.
This flowers
parents were
red and
white. No
one color
red, or white
is dominant.
Each color is
expressed or
shown.
Many Genes, One Trait
• Some traits such as the color of your
skin, hair and eyes are the result of
several genes acting together.
• Therefore it is difficult to tell if some
traits are the result of dominant or
recessive genes.