Lecture 6: What Darwin didn't know: Mendel and basic genetics

Vocabulary flashcards covering key Mendelian genetics concepts from the Mendel-based lecture.

Blending inheritance

An early idea that offspring are intermediate blends of parental traits; Mendel showed that inheritance is particulate and traits can reappear in later generations.

True breeding

A line of organisms that, when self-fertilized, produces offspring identical to itself for a given trait (homozygous for that trait).

Cross fertilize

To mate or fertilize between two different individuals to produce offspring.

Trait

A heritable characteristic that varies among individuals.

Hybrids

Offspring from crossing two true-breeding lines; typically heterozygous for the traits studied.

P generation

The parental generation in a genetic cross.

F1 generation

The first filial generation; the offspring of the P generation.

F2 generation

The offspring of a cross between F1 individuals; second filial generation.

F3 generation

The offspring of the F2 generation.

Self-cross

Self-fertilization of an individual to produce offspring with its own alleles.

Monohybrid cross

A cross examining one trait.

Punnett square

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

Genotype

The genetic makeup of an organism; the combination of alleles present.

Phenotype

The observable physical or physiological traits of an organism.

Alleles

Different forms of a gene.

Homozygous

Having two identical alleles for a gene (e.g., AA or aa).

Heterozygous

Having two different alleles for a gene (e.g., Aa).

Dominant

An allele that is expressed in the phenotype when present with another allele.

Recessive

An allele that is expressed only when two copies are present (homozygous recessive).

Mendel's 1st law (Segregation)

Alleles segregate into gametes during meiosis and rejoin randomly at fertilization.

Mendel's 2nd law (Independent assortment)

Alleles of different genes assort independently during gamete formation.

Dihybrid cross

A cross analyzing two traits simultaneously.

Dihybrid ratio 9:3:3:1

Typical phenotypic ratio from a dihybrid cross of two heterozygotes for two traits.

Gene linkage

Genes located near each other on the same chromosome tend to be inherited together, reducing independent assortment.

Polygenic inheritance

Traits controlled by multiple genes, often with additive effects.

Epistasis

Interaction where one gene masks or modifies the expression of another gene.

Pleiotropy

A single gene influencing multiple, seemingly unrelated phenotypic traits.

Incomplete dominance

A pattern where heterozygotes show an intermediate phenotype between the two homozygotes.

Codominance

Heterozygotes express both parental phenotypes simultaneously without blending.

Environmental effects on gene expression

External conditions can influence how genes are expressed.

Latent trait

A trait that is genetically determined but not expressed under certain conditions.

Two-state vs multi-state traits

Some traits are controlled by two alleles (two-state); others involve multiple alleles or states (multi-state).

Genotype vs phenotype (summary)

Genotype is the genetic makeup (alleles); phenotype is the observable trait resulting from genotype and environment.

Non-true-breeding

Organisms that are not true-breeding; typically heterozygous for studied traits.