Particulate Inheritance, Linkage, and Extensions of Mendelian Genetics

Vocabulary flashcards covering Mendelian principles, dihybrid crosses, chromosomal linkage, recombination frequency, pedigree patterns, and mechanisms of dominance.

Lawrence's Warbler ("LAWA")

A rare hybrid warbler phenotype characterized by a black throat and all-yellow underparts, which corresponds to the double recessive homozygote in the GWWA-BWWA two-locus inheritance system.

Brewster's Warbler ("BRWA")

The most common hybrid warbler phenotype, displaying a non-black throat and largely white underparts, representing the double heterozygote in the GWWA-BWWA cross.

Linked Genes

Loci located close together on the same chromosome arm that do not assort independently and are typically inherited together unless separated by a crossing-over event.

Genetic Recombination

The generation of non-parental allele combinations in gametes resulting from crossing over between homologous chromosomes during meiosis I.

Recombination Frequency

The proportion of recombinant offspring resulting from a testcross, calculated as $\frac{\text{number of recombinants}}{\text{total offspring}}$ (such as $\frac{391}{2300} = 0.17$ or $17\%$ in T.H. Morgan's Drosophila linkage crosses).

Centimorgan (Map Unit)

A unit of measure for genetic distance along a chromosome, where one map unit represents a $1\%$ recombination frequency between two loci.

Complete Dominance

A pattern of dominance where the heterozygous genotype ($Aa$) produces an identical phenotype to the homozygous dominant genotype ($AA$), as seen in Mendel's pea flower color.

Incomplete Dominance

A genetic condition in which the heterozygous phenotype ($Aa$) is an intermediate between the two homozygous phenotypes ($AA$ and $aa$), yielding identical $1:2:1$ genotypic and phenotypic ratios in the $F_2$ generation.

Codominance

A form of inheritance where both alleles in a heterozygote are simultaneously and fully expressed, producing a dual phenotype displaying both molecular products (e.g., AB blood type with $I^A$ and $I^B$ alleles).

Dominant Inheritance Pattern

A mode of genetic disorder transmission shown in pedigrees where a single copy of an abnormal allele causes the trait, every affected person has an affected parent, and approximately $\frac{1}{2}$ of the offspring of an affected parent are affected.

Recessive Inheritance Pattern

A mode of transmission where two copies of an abnormal allele are required for expression, allowing phenotypically unaffected heterozygous carrier parents to produce homozygous affected offspring.

Physiological Basis of Dominance

The biochemical relationship whereby dominance is determined by how the dose of an active gene product relates to phenotype along a saturation curve, rather than physical silencing of an allele.