Chromosomes, Linkage and Genetic Mapping: every key term you need (+ practice quiz)
25 flashcard terms for Genetics Topic 2, written to match the course framework. Study them here, then drill them as interactive flashcards, or test yourself with the 8-question quiz — free, no account needed.
The proposal that genes reside on chromosomes, confirmed when the transmission of a specific trait was shown to track a specific chromosome.
Homologous chromosomes
A matched pair carrying the same genes in the same order, one from each parent, though not necessarily the same alleles.
Sister chromatids
The two identical copies of a replicated chromosome joined at the centromere, separated at mitosis and at the second meiotic division.
Synapsis
The pairing of homologues during the first meiotic prophase, held by a protein scaffold that aligns them precisely enough for exchange.
Chiasma
The visible point where homologues remain connected after exchange. At least one per pair is needed for correct segregation.
Crossing over
Reciprocal exchange between non-sister chromatids of homologous chromosomes, producing chromosomes with new allele combinations.
Genetic linkage
Genes close together on one chromosome are inherited together more often than chance, so parental combinations exceed recombinant ones.
Recombination frequency
The proportion of offspring showing new allele combinations. It rises with distance and saturates near one half for genes far apart or on different chromosomes.
Map unit
A distance corresponding to one percent recombination. Because it is a frequency, it underestimates true physical distance across long intervals.
Coupling versus repulsion
Whether two dominant alleles entered from the same parent or from different parents. It changes which offspring classes are parental, though not the map distance.
Three-point cross
Follows three linked genes at once, giving gene order and two distances in one experiment while revealing double crossovers directly.
Double crossover class
The rarest phenotypic class in a three-point cross. Comparing it with the parental class identifies which gene lies in the middle.
Interference
The suppression of a second crossover near a first one, measured by comparing observed with expected double crossovers.
Coefficient of coincidence
The ratio of observed to expected double crossovers, which is one minus interference and equals one when crossovers are independent.
Physical versus genetic map
A physical map measures base pairs while a genetic map measures recombination, and the two diverge because crossover rate is not uniform along a chromosome.
Recombination hotspot
A short region with far higher crossover rate than its surroundings, which stretches genetic distances relative to physical ones.
Centromere position
Whether a centromere sits centrally or near one end classifies chromosome shape and affects how rearrangements are recognized.
Karyotype
The ordered display of an individual's chromosomes by size and banding, used to detect changes in number and large structural changes.
Failure of chromosomes to separate properly in division, producing gametes with an extra or missing chromosome.
Aneuploidy
An abnormal chromosome number affecting individual chromosomes rather than whole sets, usually with severe consequences because gene dosage is unbalanced.
Polyploidy
Possessing more than two complete chromosome sets. It is often tolerated in plants and can generate a new species in a single generation.
Deletion and duplication
Loss or gain of a chromosome segment. Deletions can unmask recessive alleles on the intact homologue, while duplications supply raw material for new gene functions.
Inversion
A segment reversed in orientation. It suppresses the recovery of recombinants within the inverted region, so inverted regions behave as single inherited blocks.
Translocation
A segment moved to a non-homologous chromosome. Carriers are often healthy but produce a high proportion of unbalanced gametes.
Extranuclear inheritance
Inheritance through mitochondrial or chloroplast genomes, which is typically uniparental and produces pedigrees that ignore the usual chromosomal rules.