Chapter 13: Mendel's Experiments and Heredity

Genetics

The scientific study of heredity.

Heredity

The process of passing traits from parents to offspring through genes.

Pangenesis

Early theory that "gemmules" (seeds) are released from all cells and collect in gametes.

Preformationism

The debunked belief that organisms grow directly from gametes (uniparental inheritance).

Blending Hypothesis

Darwin's idea that offspring are simply a mathematical average of both parents.

Gregor Mendel

The "Father of Genetics"; an Austrian monk who studied inheritance using pea plants.

True-breeding

Plants that, when self-fertilized, always produce offspring with the same phenotype as the parent.

F1 Generation

The first generation of offspring from a cross of true-breeding parents; usually shows only the dominant trait.

F2 Generation

The offspring resulting from the self-fertilization of the F1 generation; shows a 3:1 ratio of traits.

Alleles

Alternative versions of the same gene (e.g., Purple vs. White flowers).

Dominant Allele

The allele that is always displayed in a heterozygote, masking the other version.

Recessive Allele

The allele that is masked in a heterozygote; only expressed when two copies are present.

Law of Segregation

Principle stating that two alleles for a trait separate during meiosis so each gamete carries only one.

Homozygous

Having two identical alleles for a gene (can be dominant or recessive).

Heterozygous

Having two different alleles for a gene (one dominant, one recessive).

Genotype

The specific genetic makeup or combination of alleles in an individual.

Phenotype

The observable physical traits or characteristics of an individual.

Punnett Square

A grid used to predict the potential genotypes and phenotypes of offspring from a cross.

Monohybrid Cross

A cross between individuals that involves one specific characteristic (e.g., flower color).

Dihybrid Cross

An experiment evaluating two different characters at once to see if they are inherited together or separately.

Law of Independent Assortment

Genes for different traits assort independently of one another (only if they are on different chromosomes).

Incomplete Dominance

When heterozygotes display an intermediate, "blended" phenotype (e.g., Red x White = Pink snapdragons).

Codominance

When both alleles contribute equally and distinctly to the phenotype (e.g., AB blood type).

Epistasis

When one gene masks or interferes with the expression of a second gene (e.g., coat color in Labs).

Polygenic Inheritance

When multiple genes combine to influence a single phenotype (e.g., human skin color).

Environmental Influence

The concept that phenotype is a result of both genotype and environmental factors.

Pedigree Chart

A family tree diagram used to track the inheritance patterns of specific genetic traits.

Dominant Pattern

Inheritance where affected offspring must have at least one affected parent.

Recessive Pattern

Inheritance where affected offspring can come from two unaffected (carrier) parents.

Carrier

An unaffected heterozygote who "carries" a recessive allele and can pass it to offspring.

Overdominance

When a heterozygote has a survival advantage over both homozygotes (e.g., Sickle Cell carriers resisting Malaria).