Mendel & Patterns of Inheritance

Heredity

Transmission of traits from one generation to the next.

Genetics

The scientific study of heredit

Father of Genetics

Gregor Mendel

Why Mendel used pea plants

Many varieties, distinct traits, self-fertilization ability, controlled crosses, rapid offspring

Character

A heritable feature (e.g., flower color, eye color)

Trait

A variant of a character (e.g., purple or white flowers)

True-breeding plant

Produces identical offspring when self-pollinated

Hybrid

Offspring of two different true-breeding parents

P generation

Parental generation

F1 generation

First hybrid generation

F2 generation

Second generation (offspring of F1)

Law of Segregation

Two alleles for a trait separate during gamete formation; gametes carry only one allele.

Law of Independent Assortment

Inheritance of one trait is independent of another when genes are on different chromosomes

Monohybrid phenotypic ratio (F2)

3:1 (dominant:recessive)

Monohybrid genotypic ratio (F2)

1:2:1 (homozygous dominant : heterozygous : homozygous recessive).

Punnett square

Predicts possible gamete combinations and offspring ratios.

Testcross

Cross of an unknown dominant phenotype with a homozygous recessive to determine genotype

Incomplete dominance

Heterozygote shows intermediate phenotype (e.g., red + white = pink)

Codominance

Both alleles expressed fully (e.g., blood type AB).

Pleiotropy

One gene affects multiple traits (e.g., sickle-cell disease)

Polygenic inheritance

Multiple genes influence a single trait (e.g., skin color, height)

Epistasis

One gene affects the expression of another (e.g., coat color in labs)

Multifactorial traits

Traits influenced by genes and environment (e.g., hydrangea flower color, human height)