Vocab Flashcards
linked genes
genes located close together on the same chromosome
linkage group
a group of linked genes
nonrecombinant gametes
gamete that contains only the original combinations of alleles that were present in the parents
nonrecombinant progeny
progeny that possess only the original combinations of alleles that were present in the P generation
recombinant gametes
gamete with new combinations of alleles
recombinant progeny
progeny with new combinations of alleles formed from recombinant gametes
coupling/cis, configuration
arrangement of linked genes in which wild-type alleles of two or more genes are found on one chromosome, and mutant alleles are on the homologous chromsomes
recombination frequency
proportion of recombinant progeny produced in a cross
repulsion/trans, configuration
arrangement of two linked genes in which each of a homologous pair of chromosomes contains one wild-type (dominant) allele and one mutant (recessive) allele
genetic maps
maps of the relative distances between genetic loci, markers, or other chromosome regions determined by rates of recombination; measured in recombination frequencies or map units
physical maps
map of physical distances between loci, genetic markers, or other chromosome segments; measured in base pairs
two point test cross
cross between an individual heterozygous at two loci and an individual homozygous for recessive alleles at those loci
map units (m.u.)/centiMorgans (cM)
unit of measure for distances on a genetic map; also called a centiMorgan. one map unit equals a 1% recombination frequency
three-point test cross
cross between an individual heterozygous at three loci and an individual homozygous recessive alleles at those loci
interference
degree to which one crossover interferes with additional crossovers in the same region
coefficient of coincidence
ratio of observed double crossovers to expected double crossovers
mapping functions
mathematical function that relates recombination frequencies to actual physical distances between genes
genetic markers
any variable gene or DNA sequence used to identify a location on a genetic or physical map
linkage analysis
gene mapping based on the detection of physical linkage between genes, as measured by the rate of recombination in the progeny of a cross
genome-wide association studies
looks for nonrandom associations between the presence of a trait and alleles at many different loci scattered across a genome - that is, for associations between traits and particular suites of alleles in a population
haplotype
a specific set of linked genetic variants or alleles on a single chromosome or on part of a chromosome
linkage disequilibrium
nonrandom association between alleles in a haplotype
single-nucleotide polymorphisms (SNPs)
a site in the genome where individual members of a species differ in a single base pair
chromosome mutations
variations in the number and structure of chromosomes; often affects many genes and has large phenotypic effects
metacentric
chromosome in which the two chromosome arms are approximately the same length
submetacentric
chromosome in which the centromere is displaced toward one end, producing a short arm and a long arm
acrocentric
chromosome in which the centromere is near one end, producing a long arm at one end and a knob, or satellite, at the other end
telocentric
chromosome in which the centromere is at or very near one end
chromosome rearrangments
chromosome mutations that change the structures of individual chromosomes
chromosome duplication
mutation that doubles a segment of a chromosome
tandem duplication
chromosome rearrangement in which a duplicated chromosome segment is adjacent to the original segment
displaced duplication
chromosome rearrangement in which the duplicated segment is some distance from the original segment, either on the same chromosome or on a different one
reverse duplication
duplication of a chromosome segment in which the sequence of the duplicated segment is inverted relative to the sequence of the original segment
segmental duplications
duplicated chromosome segments larger than 1000bp
chromosome deletion
loss of a chromosome segment
pseudo dominance
expression of a normally recessive allele due to a deletion on the homologous chromosome
haploinsufficient
appearance of a mutant phenotype in an individual cell or organism that is heterozygous for a normally recessive trait
chromosome inversion
rearrangement in which a segment of a chromosome has been inverted 180 degrees
paracentric inversions
chromosome inversion that does not include the centromere in the inverted region
pericentric inversions
chromosome inversion that includes the centromere in the inverted region
position effect
dependence of the expression of a gene on the gene’s location in the genome
dicentric chromatid
chromatid that has two centromeres; produced when crossing over takes place within a paracentric inversion. the two centromeres of the dicentric chromatid are frequently pulled toward opposite poles in mitosis or meiosis, breaking the chromosome
acentric chromatid
chromatid that lacks a centromere; produced when crossing over takes place within a paracentric inversion. the acentric chromatid does not attach to a spindle microtubule and does not segregate in meiosis or mitosis, so it is usually lost after one or more rounds of cell division
dicentric bridge
structure produced when the two centromeres of a dicentric compound are pulled toward opposite poles, stretching the dicentric chromosome across the center of the nucleus. eventually, the dicentric bridge breaks as the two centromeres are pulled farther apart
translocation
(1) movement of genetic material between nonhomologous chromosomes or within the same chromosome. (2) movement of a ribosome along mRNA in the course of translation
nonreciprocal translocation
movement of a chromosome segment to a nonhomologous chromosome or chromosomal region without any (or with unequal) reciprocal exchange of segments
reciprocal translocation
reciprocal exchange of segments between two nonhomologous chromosomes
Robertsonian translocation
translocation in which the long arms of two acrocentric chromosomes become joined to a common centromere, generating a metacentric chromosome with two long arms and another chromosome with two very short arms
Fragile Sites
Constriction or gap that appears at a particular location on a chromosome when cells are cultured under special conditions
fragile-x syndrome
a form of x-linked intellectual disability that appears primarily in males; associated with a fragile site that results from an expanding trinucleotide repeat
copy-number variants
difference among individual organisms in the number of copies of any large DNA sequence (larger than 1000 bp)
structural variants
collective term for chromosome rearrangements and copy-number variants
aneuploidy
change in the number of individual chromosomes; most often an increase or decrease of one or two chromosomes
polyploidy
possession of more than two sets of chromsomes
nondisjunction
failure of homologous chromosomes or sister chromatids to separate in meiosis or mitosis
nullisomy
absence of both members of a homologous pair of chromosomes (2n-2)
monosomy
absence of one of the chromosomes of a homologous pair
trisomy
presence of an extra copy of a chromosome (2n + 1)
tetrasomy
presence of two extra copies of a chromosome (2n + 2)
Down Syndrome / Trisomy 21
human condition characterized by variable degrees of intellectual disability; characteristic facial features; slower growth and development; an an increased incidence of heart defects, leukemia, and other abnormalities. it is caused by the duplication of all or part of chromosome 21
primary down syndrome
human condition caused by the presence of three copies of chromosome 21
familial down syndrome
human condition caused by Robertsonian translocation in which the long arm of chromosome 21 is translocated to another chromosome; tends to run in families
translocation carriers
individual organism heterozygous for a chromosome translocation
Trisomy 18 / Edwards Syndrome
human condition characterized by severe intellectual disability, low set ears, a short neck, deformed feet, clenched fingers, heart problems, and other disabilities; results from the presence of three copies of chromosome 18
Trisomy 13 / Patau Syndrome
human condition characterized by severe intellectual disability, small head, sloping forehead, small eyes, cleft lop and palate, extra fingers and toes, and other disabilities; results from the presence of 3 copies of chromosome 13
Trisomy 8
presence of the 3 copies of chromosome 8; in humans, results in intellectual disability, contracted fingers and toes, low-set malformed ears, and a prominent forehead
autopolyploidy
condition in which all the sets of chromosomes of a polyploid individual are derived from a single species
allopolyploidy
condition in which all chromosomes of a polyploid individual are from two or more species
unbalanced gametes
gamete that has a variable number of chromosomes; some chromosomes may be missing and others may be present in more than one copy
amphidiploid
type of allopolyploid in which two different diploid genomes are combined such that every chromosome has one and only one homologous partner and the genome is functionally diploid
quantitative genetics
genetic analysis of complex characteristics
meristic characteristics
Characteristic whose phenotype varies in whole numbers of vertebrae, but may be caused by continuous genetic variation
threshold characteristic
Characteristic that has only two phenotypes (presence and absence) but whose expression depends on an underlying susceptibility that varies continuously
frequency distribution
a concise graphical method of summarizing values. In genetics, the phenotypes found in a group of individuals are usually displayed as a frequency distribution. Typically, the phenotypic classes are plotted on the horizontal (x) axis, and the numbers (or proportions) of individuals in each class are plotted on the vertical (y) axis
normal distribution
common type of frequency distribution that exhibits a symmetrical, bell-shaped curve; usually arises when a large number of independent factors contribute to a measured value
mean
statistic that provides information about the center of a distribution of measurements; calculated by adding all the individual measurements and dividing by the total number of measurements; also called the average
variance
statistic that describes the variability of a group of measurements
Heritability
proportion of total phenotypic variation that is due to genetic differences
phenotypic variance
measure of the degree of phenotypic difference among a group of individuals; composed of genetic, environmental, and genetic-environmental interaction variances
genetic variance
component of phenotypic variance that is due to genetic differences among individual members of a population
environmental variance
component of phenotypic variance that is due to environmental differences among individual members of a population
Additive genetic variance
Component of genetic variance that comprises the additive effects of genes on the phenotype
genetic-environmental interaction variance
Component of phenotypic variance that results from an interaction between genotype and environment that causes genotypes to be expressed differently in different environments
Dominance genetic variance
Component of genetic variance that can be attributed to dominance (interaction between genes at the same locus)
Gene interaction variance
Component of genetic variance that can be attributed to gene interaction (interaction between genes at different loci)
Broad-sense heritability
Proportion of phenotypic variance that can be attributed to genetic variance
Narrow-sense heritability
Proportion of phenotypic variance that results from the additive genetic variance
Quantitative trait loci (QTLs)
a chromosomal region containing genes that control polygenic characteristics
Natural Selection
differential reproduction of individuals with different genotypes
Artificial Selection
selection practiced by humans
response to selection
the extent to which a characteristic subjected to section changes in one generation; equals the selection differential times the narrow-sense heritability
selection differential
difference between the mean phenotype of the selected parents and the mean phenotype of the original population
realized heritability
heritability determined by a response-to-selection experiment
genotypic frequency
proportion of a particular genotype within a population
allelic frequencies
proportion of a particular allele within a population
Hardy-Weinberg Law
principle of population genetics stating that if a population is large, randomly mating, and not affected by mutation, migration, or natural selection, then allelic frequencies of a population do not change and the genotypic frequences stabilize after one generation in the proportions p^2 (the frequency of AA) 2pq (the frequency of Aa), and q^2 (the frequency of aa), where p equals the frequency of allele A and q equals the frequency of allele a
Hardy-Weinberg equilibrium
frequencies of genotypes when the conditions of the Hardy-Weinberg law are met
inbreeding
a form of nonrandom mating; preferential mating between related individuals
inbreeding depression
decreased fitness arising from inbreeding; often due to the increased appearance of lethal or deleterious traits with inbreeding
equilibrium
situation in which no further change takes place; in population genetics, refers to a population in which allelic frequencies do not change
migration / gene flow
movement of genes from one population to another
sampling error
deviations from expected ratios due to chance when the sample size is small
genetic drift
change in allelic frequencies due to a sampling error
effective population size (Ne)
effective number of breeding adults in a population; influenced by the number of individuals contributing genes to the next generation, their sex ratio, variation between individuals in reproductive success, fluctuations in population size, age structure of the population, and whether mating is random
founder effect
sampling error that results from the establishment of a population by a small number of individuals; leads to genetic drift
genetic bottleneck
sampling error that arises when a population undergoes a drastic reduction in size; leads to genetic drift
fixation
when one allele reaches a frequency of 1 in a population, at which point all individuals in the population are homozygous for one allele
fitness
reproductive success of a genotype relative to that of other genotypes in a population
selection coefficient (s)
measure of the relative intensity of selection against a genotype; equals 1 minus W (fitness value)
directional selection
selection in which one allele or trait is favored over another
overdominance / heterozygote advantage
selection in which the heterozygote has higher fitness than either homozygote
under dominance
selection in which the heterozygote has lower fitness than either homozygote
neutral-mutation hypothesis
proposal that much of the molecular variation seen in natural populations is adaptively neutral and unaffected by natural selection; that is, that individuals with different molecular variants have equal fitness
molecular clock
use of molecular differences to estimate the time of evolutionary divergence between organisms; assumes a roughly constant rate at which one neutral mutation replaces another
multigene families
set of genes similar in sequence that arose through repeated duplication events and often encode different protein products
