Patterns of Inheritance

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

Mendel's Law 1

Law of Segregation

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

Mendel's Law 2

Law of Independent Assortment

Different traits are inherited independently of one another.

Mendel's Law 3

Law of Dominance

Dominant alleles mask recessive alleles in heterozygous individuals.

Genotype vs Phenotype

Genotype = genetic makeup (letters)

Phenotype = what you see

Punnett Squares & Ratios

Used to predict offspring outcomes.

Steps for Punnett Squares and Ratios

Identify parent genotypes

List possible gametes

Fill in combinations

Determine ratios or percents for either phenotype or genotype

Example of crosses

Heterozygous × heterozygous

Heterozygous × homozygous recessive

Heterozygous × homozygous dominant

Meiosis & Genetic Variation

Produces gametes (sperm/egg)

Cuts chromosome number in half

Creates variation through independent assortment & crossing over

What is complete dominance in inheritance?

One allele completely masks the other.

What is incomplete dominance in inheritance?

Traits blend together.

Give an example of incomplete dominance.

Blue + yellow → green appearance.

What is codominance in inheritance?

Both traits appear at the same time.

Give an example of codominance.

Spotted animals with both colors visible.

Why do sex-linked traits often appear more in males?

Males have only one X chromosome.

Pedigrees

Models/family trees that track the inheritance of traits over many generations

Autosomal Gene

Found on non sex chromosomes (1-22)

Genetic Disorders

Inherited conditions caused by mutations to genes or chromosomal defects