Inherited Traits

The Law of Dominance

Questions to Ponder…

• Why do some people look like their parents

or grandparents?

• How is it possible for a blond-haired child to

have two brown-haired parents?

• Why do brothers in one family resemble

each other and in one family have no

resemblance?

Gregor Mendel –1860s

• Grew up on a farm in Austria

and became a monk

• Observed pea plants and

wondered why generations

passed on traits he observed

• Experimented with pea

plants and learned many

things related to heredity

• Father of Modern Genetics

Dominant and Recessive Traits Handout

Dominant & Recessive Traits• Dominant traits are

“stronger” and more

likely to be visible

• Recessive traits are

“weaker” and less likely

to be visible

• Law of Dominance:

dominant traits “trump”

recessive traits

Dominant & Recessive Traits• Genes occur in pairs (alleles)

• The combination of gene pairs

determines the offspring’s phenotype

(physical trait)

• One gene comes from the mother

and the other comes from the father

Dominant & Recessive Traits

• Offspring receives…

– dominant trait from

mother

– dominant trait from

father

• Offspring phenotype

is…

– dominant trait

• Curly hair is dominant

& straight hair is

recessive

• A boy inherits the

gene for curly hair

from both his mother

and father, and he

has curly hair

Dominant & Recessive Traits

• Offspring receives…

– dominant trait from

mother

– recessive trait from

father

• Offspring phenotype

is…

– dominant trait

• Curly hair is dominant

& straight hair is

recessive

• A girl inherits curly

hair from her mother

but straight hair from

her father, and she

has curly hair

Dominant & Recessive Traits

• Offspring receives…

– recessive trait from

mother

– recessive trait from

father

• Offspring phenotype

is…

– recessive trait

• Curly hair is dominant

& straight hair is

recessive

• A boy inherits straight

hair from both his

mother and father,

and he has straight

hair

Dominant & Recessive Traits

• dominant + dominant = dominant

– homozygous: gene pairs (alleles) are the same

• dominant + recessive = dominant

– heterozygous: gene pairs (alleles) are different

• recessive + recessive = recessive

– homozygous

Dominant & Recessive Traits

• Genes occur in pairs, alleles

• The combination of gene pairs

(genotype) determines the

offspring’s phenotype

• One gene comes from the mother

and the other comes from the father

Dominant & Recessive Traits

• dominant + dominant = dominant

– homozygous: gene pairs (alleles) are the same

– Height in Pea Plants: TT genotype

• dominant + recessive = dominant

– heterozygous: gene pairs (alleles) are different

– Height in Pea Plants: Tt genotype

• recessive + recessive = recessive

– homozygous

– Height in Pea Plants: tt genotype

Application• Charlie cannot roll his tongue. His

mother cannot roll her tongue.

– Can you determine his father’s

phenotype?

– Can you determine any of their

genotypes?

Application

• Maria has unattached ear lobes. Her

father has attached ear lobes.

–Can you determine any of their

phenotypes?

–Can you determine any of their genotypes?

–Can you determine if Maria could have a

child with attached ear lobes?

Application

• Mr. Henderson has a bent little finger, and

so does his wife, Mrs. Henderson.

– Can you determine any of their phenotypes?

– Is it possible for their son and daughter to

have different phenotypes?

– Can you determine any of their genotypes?