Gentics

Gene

Basic functional unit of inheritance.

Phenotype

Observable trait or characteristic of an organism (e.g., flower color).

Character / Trait

A specific biological property (e.g., locomotion, flower color).

Wild type

The most common, naturally occurring form of a trait.

Mutant

A heritable variant differing from the wild type.

Single-gene inheritance

A trait controlled by one gene, shown by specific inheritance patterns.

Heritable variants

Inherited traits that differ from the standard form (wild type).

Wild Type

The most common, naturally occurring form of a trait in a species.

Mutation (event)

A heritable change in DNA that alters a gene.

Mutation (gene)

The altered form of the gene after mutation.

Genetic dissection

Using mutants to "break down" a complex trait into its genetic components.

Forward genetics

Approach where researchers start with observable mutant phenotypes and work toward identifying the genes and their functions.

Reverse genetics

Starts with known genes (via DNA analysis), then creates specific mutations to see how they affect the phenotype.

Phenotypic ratio

The ratio of different observable traits (phenotypes) seen in offspring from a cross.

Controlled cross

A mating between organisms where the parents' genotypes and traits are known.

Pure line (true breeding)

A group of genetically identical organisms that always produce offspring with the same trait when crossed with each other.

Contrasting phenotypes

Two clearly different observable traits for the same character (e.g., yellow vs. green seeds).

9-3-3-1 Ratio

Dihybrid Cross

• 9: Dominant for both traits (round yellow)

• 3: Dominant for the first trait, recessive for the second (round green)

• 3: Recessive for the first trait, dominant for the second (wrinkled yellow)

• 1: Recessive for both traits (wrinkled green)

3-1 Ratio

Monohybrid Cross - 3 Dom, 1 Rec

1-1-1-1 Ratio

Monohybrid Cross with Heterozygous Parents

Homozygote

An individual with two identical alleles (e.g., Y/Y or y/y).

Heterozygote

An individual with two different alleles (e.g., Y/y).

Genotype

The genetic makeup of an individual (e.g., Y/Y, Y/y, y/y).

Phenotype

The observable trait (e.g., yellow or green seeds).

Monohybrid cross

A cross between two heterozygotes for a single gene (Y/y × Y/y).

Mendel’s First Law (Law of Equal Segregation)

During meiosis, alleles of a gene pair separate equally into gametes. Each gamete gets one allele. Explains the 3:1 ratio and 1:2:1 genotypic ratio in the F₂ generation of a monohybrid cross.

Heterozygote

Two different alleles (e.g., Y/y)

Homozygote

Two same alleles (e.g., y/y or Y/Y)

Somatic cells

All non-reproductive cells in an organism.

Gametes

Reproductive cells (sperm, eggs, spores) with half the full chromosome set.

Meiocytes

Cells in sex organs that undergo meiosis to produce gametes. AKA - Specialized cells in sex organs that undergo meiosis to form gametes.