Patterns of Inhertiance

Gene

A segment of DNA that codes for a specific trait

Allele

Different forms of a gene (ex: A or a)

Trait

A specific characteristic (ex: hair color, height)

Cross

A mating of 2 organisms

Chromosome

Structure made of DNA that carries genes

Genotype

The allele combination an organism has (ex: Bb)

Phenotype

The observable traits (ex: brown eyes)

Homozygous

Two identical alleles (AA or aa)

Heterozygous

Two different alleles (Aa)

Dominant allele

Expressed when at least one copy is present

Recessive allele

Only expressed when two copies are present

Codominance

Both alleles are fully expressed (ex: both traits visible)

Incomplete dominance

Blended phenotype (ex: red + white → pink)

Polygenic trait

Controlled by multiple genes (ex: skin color)

Sex-linked trait

Trait located on sex chromosomes (often X-linked)

Meiosis

Cell division that produces gametes with half the chromosomes

Law of Segregation

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

Law of Independent Assortment

Different traits are inherited independently of one another.

Law of Dominance

Dominant alleles mask recessive alleles in heterozygous individuals.

Genotype vs Phenotype

Genotype = genetic makeup (letters); Phenotype = what you see

Punnett Squares

Used to predict offspring outcomes.

Complete Dominance

One allele completely masks the other

Sex-Linked Traits

Often appear more in males because they have only one X chromosome

Meiosis & Genetic Variation

Produces gametes (sperm/egg), cuts chromosome number in half, creates variation through independent assortment & crossing over