Mr. AltorferScience

Traits and InheritancePages 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.