Genetics

Phenotype

Physical traits an organism shows (what you can see).

Genotype

The allele combination an organism has.

Allele

Different forms of the same gene.

Dominant Allele

An allele that is expressed whenever it is present.

Recessive Allele

An allele that is only expressed when two copies are present.

Homozygous Dominant

Two dominant alleles (AA).

Homozygous Recessive

Two recessive alleles (aa).

Heterozygous

One dominant and one recessive allele (Aa).

Carrier

A person who has one recessive allele but does not show the trait.

S*x-Linked Trait

A trait carried on the X chromosome.

Autosome

Any chromosome that is not a s*x chromosome.

Autosomal Dominant

Trait is on an autosome and only one dominant allele is needed.

Autosomal Recessive

Trait is on an autosome and requires two recessive alleles.

Test Cross

Crossing an organism with a homozygous recessive individual to determine its genotype.

What does a Punnett square predict?

Possible offspring genotypes and phenotypes.

Genotype Ratio

Ratio of offspring genotypes.

Phenotype Ratio

Ratio of offspring phenotypes.

Monohybrid Cross

Cross involving one trait.

Dihybrid Cross

Cross involving two traits.

What is simple dominance?

The dominant allele completely masks the recessive allele.

Example of simple dominance

Purple flowers dominant over white flowers.

AA genotype phenotype

Dominant trait.

Aa genotype phenotype

Dominant trait

aa genotype phenotype

Recessive trait.

Genotype ratio of Aa × Aa

1 AA : 2 Aa : 1 aa.

Phenotype ratio of Aa × Aa

3 dominant : 1 recessive.

Dihybrid cross example

AaBb × AaBb.

How many boxes are in a dihybrid Punnett square?

16

Phenotype ratio of AaBb × AaBb

9 : 3 : 3 : 1

Law of Independent Assortment

Alleles for different genes separate independently during gamete formation.

What chromosome usually carries s*x-linked traits?

X chromosome.

Why are males more likely to show s*x-linked recessive traits?

They only have one X chromosome.

Male genotype

XY

Female genotype

XX

Hemophilia is what type of inheritance

S*x linked recessive

Color blindness is what type of inheritance?

S*x linked recessive

Muscular dystrophy is what type of inheritance?

S*x linked recessive

Male pattern baldness (for this class)

S*x linked recessive

Female carrier genotype for hemophilia

XᴴXʰ.

Hemophiliac male genotype

XʰY.

Why can't fathers pass X-linked traits to sons?

Fathers give sons a Y chromosome.

What is incomplete dominance?

Neither allele completely masks the other.

Result of incomplete dominance

Blended phenotype.

Red flower × White flower

Pink flower.

Genotype ratio in incomplete dominance cross

1 : 2 : 1.

Phenotype ratio in incomplete dominance cross

1 : 2 : 1

Difference between simple dominance and incomplete dominance

Simple dominance masks recessive allele; incomplete dominance creates a blend.

What is codominance?

Both alleles are fully expressed.

Example of codominance

Roan cattle.

Another example of codominance

Spotted dogs.

Blood type AB demonstrates

Codominance

Difference between codominance and incomplete dominance

Codominance shows both traits; incomplete dominance blends them.

What are multiple alleles?

A trait controlled by three or more alleles.

Example of multiple alleles

Blood type.

Blood type alleles

A, B, O

Which blood type is codominant?

AB

Universal blood recipient

AB

Universal blood donor

What is a polygenic trait?

A trait controlled by multiple genes.

How do polygenic traits differ from Mendelian traits?

Multiple genes influence one trait.

Example of a polygenic trait

Height

Another polygenic trait

Skin color.

Another polygenic trait

Hair color.

Another polygenic trait

Eye color.

Why do polygenic traits show many variations?

Multiple genes contribute to the phenotype.

If a trait is controlled by 2 genes, how many alleles influence it?

4 alleles

If a trait is controlled by 3 genes, how many alleles influence it?

6 alleles

Hemophilia

S*x-linked recessive.

Color blindness

S*x-linked recessive.

Muscular Dystrophy

S*x linked recessive

Sickle Cell Disease

Autosomal recessive

Cystic fibrosis

Autosomal recessive.

huntingtons disease

Autosomal recessive.

Achondroplasia (dwarfism)

Autosomal recessive.

Tay-Sachs Disease

Autosomal recessive.

Why are recessive disorders often hidden?

Carriers do not show symptoms.

What cross produces a 3:1 phenotype ratio?

Aa × Aa.

What cross produces a 1:2:1 genotype ratio?

Aa × Aa.

What cross is used to determine an unknown genotype?

Test cross.

What is the phenotype ratio of a dihybrid cross?

9:3:3:1.

Which inheritance pattern produces a blend?

Incomplete dominance.

Which inheritance pattern expresses both alleles equally?

Codominance

Which blood type is codominant?

AB

Which inheritance pattern is color blindness?

S*x-linked recessive.

Which inheritance pattern is hemophilia?

S*x-linked recessive.

Which inheritance pattern is Huntington's disease?

Autosomal dominant.

Who is known as the Father of Genetics?

Gregor Mendel

What organism did Mendel use in his experiments?

Pea plants

Why did Mendel use pea plants

They reproduce quickly, have many traits, and can self-pollinate or cross-pollinate.

What is Mendel's Law of Segregation?

Alleles separate during gamete formation so each gamete gets one allele.

What is Mendel's Law of Independent Assortment?

Alleles for different traits separate independently.

What did Mendel discover about dominant and recessive traits?

Dominant traits mask recessive traits.