Genetics: Independent Assortment, Recombination, and Inheritance Patterns

Vocabulary-style flashcards covering dihybrid crosses, independent assortment, recombination frequency, polygenic inheritance, organelle inheritance, and extensions of Mendelian inheritance such as dominance types.

Dihybrid cross

A cross between plants that differ in two traits, which typically results in an F2 phenotype ratio of $9:3:3:1$.

Independent Assortment

The principle that homologous chromosomes carrying different genes (e.g., $S$ and $Y$) separate independently during meiosis, producing four gamete types ($SY$, $Sy$, $sY$, $sy$) with equal probability.

Meiotic Recombination

A process where the meiotic output (gametes) is different from the meiotic input (parental types), resulting in recombinant genotypes.

Testcross for Recombination

A cross between a dihybrid ($A/a \cdot B/b$) and a homozygous recessive "tester" ($a/a \cdot b/b$) used to identify meiotic output.

Recombination Frequency of $50\%$

The specific frequency percentage that indicates independent assortment has occurred between genes.

Polygenic Inheritance

An inheritance pattern involving multiple Mendelian genes that affect the same trait, often resulting in continuous variation and a bell curve distribution.

Quantitative Trait Loci (QTLs)

Another name for polygenes, which are located on different chromosomes and assort independently.

Organelle inheritance

The inheritance of genomes found in mitochondria and chloroplasts, which are inherited via the cytoplasm in a uniparental (maternal) manner.

Cytoplasmic segregation

The distribution of organelles carrying different alleles (e.g., allele $A$ vs. allele $a$) into different cells during division, often observed in variegated plants.

MELAS

A mitochondrial DNA disease standing for Mitochondrial encephalomyopathy, lactic acidosis, and strokelike symptoms.

LHON

Leber hereditary optic neuropathy, a disease caused by mutations in human mtDNA.

Complete dominance

An allele relationship where the heterozygote ($Ss$) has the same phenotype as the homozygote ($SS$); often described as haplo-sufficient.

Haplo-insufficient

A condition where a single dose of a gene product in a heterozygote is inadequate to produce the wild-type phenotype, leading to a dominant mutant allele.

Dominant negative

A mutation where the mutant allele produces a product that interferes with the function of the wild-type product, such as in Brittle Bone Disease.

Incomplete Dominance

A situation where the heterozygote has an intermediate phenotype (e.g., a pink flower resulting from red $AA$ and ivory $aa$ parents).