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.