Beh Genetics Exam 1
passive gene-environment correlation
A correlation between genetic and environmental influences that occurs when children inherit genes with effects that covary with parents' environment; parents provide both genes and environment
active genotype-environment correlation
A correlation between genetic and environmental influences that occurs when individuals select or construct environments with effects that covary with their genetic propensities
inbred strain
A strain of animal that has been created by mating brothers and sisters for at least 20 generations, resulting in nearly genetically identical individuals
Genome
All the DNA sequences of an organism. Contains about 3 billion DNA base pairs
sex chromosomes
Chromosomes that determine the sex of an individual
transcription
DNA into a different sort of nucleic acid called ribonucleic acid or RNA
independent assortment
Mendel's second law of heredity. States that the inheritance of genes at one locus is not affected by the inheritance of genes at another locus.
phenotypes
Physical expressions of genetic trait
Translation
RNA is synthesized into proteins
DNA markers
Sequences of bases occurring at specific loci on specific chromosomes: used to show that a certain gene is on a chromosome
equal environments assumption
The assumption that the environments experienced by identical twins are no more similar to each other than are the environments experienced by fraternal twins. If they are more similar, then the greater similarity of the identical twins could plausibly be due to the fact that they experience more similar environments rather than the fact that they have more genes in common.
Exceptions to independent assortment
When genes are inherited which are close together on the same chromosome (linkage)
Nondisjunction
a common copying error for chromosomes is an uneven split of the pairs of chromosomes during meisosis
evocative genotype-environment correlations
a correlation between genetic and environmental influences that occurs when individuals evoke environmental effects that covary with their genetic propensities
pedigrees
a family tree diagram depicting the genealogical history of a family, especially showing the inheritance of a particular condition in the family members
carrier
a female with one copy of a recessive X-linked allele; can pass it on to offspring
mutations
a heritable change in DNA base pair sequences
amniocentesis
a medical procedure used for prenatal diagnosis in which a small amount of amniotic fluid is extracted from the amnion surrounding a developing fetus. BC some of the fluid contains cells from the fetus, fetal chromosomes can be examined and fetal genes can be tested
genome wide gene by environment interaction
a method for searching for genotype-environment interaction that assesses DNA variation throughout the genome
recombination
a process that occurs during meiosis in which chromosomes exchange parts; occurs in the ovaries and testes when gametes are produced
adoption study
a range of studies that use the separation of biological and social parentage brought about by adoption to assess the relative importance of genetic and environmental influences. The strategy commonly involves a comparison of adoptees' resemblance to their biological parents. May also involve the comparison of genetically related siblings and genetically unrelated adoptive siblings reared in same family
triplet codons
a sequence of three base pairs that codes for a particular amino acids or the end of a chain. aka as triplet nucleotides.
morbidity risk estimate
a special incidence figure used in genetic studies that shows the chance of being affected during an entire lifetime
genetic correlation (rG) between traits
a statistic indexing the extent to which genetic influences on one trait are correlated with genetic influences on another trait independent of the heritabilities of the traits
chromosome
a structure that is composed mainly of chromatin, which contains DNA and resides in nucleus of cells
model fitting
a technique for testing the fit between a model of genetic and environmental relatedness against the observed data. different models can be compared, and the best fitting model is used to estimate genetic and environmental parameters
polygenic trait
a trait influenced by multiple genes
Hardy-Weinberg equilibrium
allele and genotype frequencies in a population will remain constant from generation to generation in the absence of other evolutionary influences (migration or natural selection). The frequencies of alleles and genotypes do not change across generations unless forces change them
qualitative disorders
an all or nothing descriptor
recessive allele
an allele that produces its phenotype only when two copies are present
allele
an alternative form of a gene at a locus
instincts
an behavioral tendency
index case/proband
an individual in the center of a genetic relatedness model
autosomes
any chromosome other than the X and Y sex chromosomes. Humans have 22 pairs of these chromosomes and 1 pair of sex chromosomes.
family study
assessing the resemblance between genetically related parents and offspring, and between siblings living together. Resemblance can be due to hereditary or to shared family environment
liability-threshold model
assumes that risk is distributed normally but that the disorder only occurs when a certain threshold of liability is exceeded
selective breeding
breeding for a phenotype over several generations by selecting parents with high scores on the phenotype, mating them, and assessing their offspring to determine the response to selection. Bidirectional selection studies also select in the other direction (for low scores)
linkage analysis
can be used to identify the location of a gene on a particular chromosome. Techniques that use info about violations of independent assortment to identify the chromosomal location of a gene. DNA markers serve as signposts on chromosomes = looks for a violation of independent assortment between a trait and a DNA marker to assess whether the DNA marker and the trait co-assort in a family more often than expected by chance
messenger RNA
carries genetic code contained in the sequence of DNA bases to enable it to be translated into amino acid sequences. Consists of codons: various sequences of the 6 bases (relays DNA code and leaves the nucleus and enters cell body where it connects with ribosomes)
carriers
carry an allele, but are not affected themselves, and can pass it on to their offspring
crossover
chromatids do this to exchange parts during recombination
genotype
combinations of alleles
twin study
compares the resemblance within pairs of identical twins who are genetically identical to the resemblance within pairs of fraternal twins, who are 50% similar genetically
quantitative genetics
continuously distributed in the familiar bell-shaped curve, with most people in the middle and fewer people toward the extremes, not "all or nothing"
twin correlation
correlation of twin 1 with twin 2. Typically computed separately for MZ and DZ twins. Used to estimate genetic and environmental influences
monozygotic twins
derived from one fertilized egg (zygote) and are genetically identical
correlation
describes relationship between 2 variables; an index of resemblance that ranges from -1 to 1, where 0 indicates no resemblance
mapping
determining where certain genes are located
dizygotic twins
develop from separately fertilized eggs
DNA
double-stranded molecule that encodes genetic info; the 2 strand held together by hydrogen bonds between 2 of the 4 bases (adenine to thymine and cytosine to guanine)
SNP heritability
estimated directly from DNA differences between individuals
bivariate heritability
estimates the contribution of genetic influences to the phenotypic correlation between the two traits
quantitative genetics
estimates the extent to which observed differences among individuals are due to genetic differences of any sort and to environmental differences of any sort without specifying what the specific genes or environmental factors are
non-shared environmental influences
factors that contribute to differences among family members; all nongenetic influences that are independent or uncorrelated for family members; including error of measurement; the only thing that can account for differences between identical twins reared together
genotype-environment interaction
genetic sensitivity or susceptibility to environments. Usually limited to statistical interactions, such as genetic effects that differ in different environments. The association between a genotype and a phenotype might differ in different environments
candidate gene by environment interaction
genotype environment interaction in which an association between particular gene and a phenotype differs in different environments
second-degree relative
grandparent, aunt, uncle
effect size
how much genetics contributes to a trait; the extent to which individual differences for the trait in the population can be accounted for by genetic differences among individuals
knock-out gene
inactivation of a gene by gene targeting
diathesis-stress model
individuals at genetic risk for psychopathology are especially sensitive to the effects of stressful environments
half siblings
individuals who have just one biological birth parent in common
full siblings
individuals who have two biological parents in common
targeted mutations
knockout the expression of specific genes; a process by which a gene is changed in a specific way to alter its function, such as knock-outs. Called transgenics when the mutated gene is transferred from another species
linkage
loci that are close together on a chromosome and thus inherit together within families. An exception to Mendel's second law of independent assortment
centimorgan
measure of genetic distance on a chromosome. Two loci are 1 cM apart if there is a 1 percent chance of recombination due to crossover in a single generation. 1 cM corresponds to 1 million base pairs in humans.
gene targeting
mutations that are created in a specific gene and can then be transferred to an embryo
shared environment
nongenetic influences that are correlated for family members
adoptive siblings
not from the same biological parents but in same environment
chromatids
one of the two copies of DNA making up duplicated chromosome, which are joined at their centromeres for the process of cell division (meiosis and mitosis). Normally identical but may have slight differences in the case of mutations. Called sisters as long as they are joined by the centromeres, during which time they can recombine. When they separate, the strands are called daughter chromosomes.
chorion
outermost layer of the fetal membrane (sac within the placenta)
first degree relative
parent or sibling or child
GE correlation (rGE)
people with different genotypes are not exposed to environments at random. Environmental exposure depends on characteristics of a person. Experiences that are correlated with genetic propensities.
selective placement
placing adopted-apart "genetic" relatives into correlated environments, matching the biological and adoptive parents
allelic frequencies
population frequency of an alternate form of a gene. For example, the frequency of the PKU allele is about 1 percent
environmentality
proportion of phenotypic variance that can be accounted for by environmental influences; parents resemble offspring because they provide the home environment and siblings resemble one another because they live in it together
Broad-sense heritability
proportion of the phenotypic variance that can be attributed to genetic variance (involves all additive and non-additive sources of genetic variance)
Narrow-sense heritability
proportion of the phenotypic variance that can be attributed to solely additive genetic variance
multivariate genetic analysis
quantitative genetic analysis of the covariance between traits
gametes
sex cells
x-linked
sex-linked (more common in males than females because females would have to have the correct allele on both X chromosomes to exhibit the trait, whereas men automatically get the mothers X)
inbreeding
sisters are mated with brothers for at least 20 generations to make each animal within the strain virtually a genetic clone of all others within the genetic strain
Structural Equation Modeling (SEM)
statistical method for testing a conceptual or theoretical model, in behavioral genetics this method is used to estimate heritability and environmentality based on the similarity and differences among family members
gene silencing
suppressing expression of a gene but not altering it and thus not heritable
genes
the basic units of heredity; a sequence of DNA bases that codes for particular product and sequences that regulate transcription
natural selection
the driving force in evolution in which the frequency of alleles change as a function of the differential reproduction of individuals and survival of offspring
pleiotropy
the effect of a single gene on many traits
genetic relatedness
the extent to which relatives have genes in common. First degree relatives are 50% similar genetically. Second degree are 25% similar. Third-degree are 12.5% similar genetically.
genotype frequency
the frequency of alleles considered two at a time as they are inherited in individuals. The genotypic frequency of PKU individuals (homozygous of the recessive PKU allele) is .0001.
nucleus
the part of the cell that contains chromosomes
concordance
the presence of the same trait in both members of a twin pair. Used to estimate risk for disorder
genomic imprinting
the process by which an allele at a given locus is expressed differently depending on whether it is inherited from the mother or the father
meiosis
the process by which gametes undergo replication/ division to form 4 haploids, so that each gamete contains only one member of each chromosome pair
segregation
the process by which two alleles at a locus, one from each parent, separate during heredity. Mendel's law of segregation is his first law of heredity.
Heritability
the proportion of phenotype differences among individuals that can be attributed to genetic differences
locus
the site of specific gene on a chromosome
population genetics
the study of allelic and genotypic frequencies in populations and the forces that change these frequencies such as natural selection
assortative mating
the type of mating that occurs when an organism selects a mating partner that resembles itself; nonrandom mating that results in similarity between spouses: can be negative (opposites attract) but usually is positive (they resemble one another)
transfer RNA
type of RNA that carries each amino acid to a ribosome during protein synthesis as dictated by base sequence of mRNA
amino acids
units of proteins; the building blocks of proteins; present in many foods in human diet
DeFries-Fulker (DF) extremes analysis
used to investigate the links between normal and abnormal. An analysis of familial resemblance that takes advantage of quantitative scores of the relatives of probands rather than just assigning a dichotomous diagnosis to the relatives and assessing concordance.