Bio 133: Exam 2 - HW
Twin studies have been important for understanding the contribution of genetics and the environment to multifactorial traits. Choose the term that best completes each of the following statements about twin studies.
1. Identical twins are also called twins. 2. Among pairs of twins in whom at least one has a particular trait, the of the trait is equal to the percentage of pairs in which both twins express the trait. 3. Twins who differ in a trait are for the trait. 4. Diseases caused by single genes that approach 100 percent penetrance approach concordance in monozygotic twins. 5. Among dizygotic twins, concordance is usually around for a dominant trait. 6. Among dizygotic twins, concordance is usually around for a recessive trait. 7. For a polygenic trait with little or no environmental influence, the concordance value for monozygotic twins will be the concordance value for dizygotic twins. 8. To assess the genetic component of a multifactorial trait, it would be most appropriate to study .
T/F 1. Genes control the synthesis of and response to neurotransmitters. 2. Different mental and behavioral conditions can have the same symptoms. 3. Behavioral disorders are usually single-gene disorders. 4. Environmental influences can affect behavioral traits. 5. Each gene that has been implicated in behavioral traits is important in just a single behavioral disorder.
1. T 2. T 3. F (many genes) 4. T 5. F (multiple disorders)
1. A trait that is influenced by two or more genes is a ____ trait. 2. A trait that is influenced by both genes and the environment is a ____ trait. 3. A trait that is influenced by only one gene is a ____ trait. 4. DNA sequences that contribute to polygenic traits are called ______.
1. polygenic 2. multifactorial 3. Mendelian 4. quantitative trait loci
diseases caused by single genes that approach 100% penetrance approach _____ concordance in monozygotic twins
100%
The proportion of shared genes between a grandparent and grandchild is _____ percent.
25
among dizygotic twins, concordance is usually around _____ for a recessive trait
25
A brother and sister share _____ percent of their genes.
50
among dizygotic twins, concordance is usually around _____ for a dominant trait
50
T/F Polygenic traits have all-or-none phenotypes.
F single gene traits have all-or-none phenotypes. Polygenic traits are continuous and vary continuously.
T/F The individual genes that contribute to a polygenic trait are dominant or recessive to each other.
F alleles of different genes can influence the same phenotype but are not dominant or recessive to another
T/F If a trait is determined entirely by genes, not by the environment, then the heritability of the trait is 0.
F (1.0)
T/F If the heritability of a trait is very high, then all siblings will have the same phenotype.
F (50%)
T/F When a trait is polygenic, individuals cannot be categorized into classes with respect to their phenotypes.
F (classes then categories)
T/F All genes that influence a polygenic trait contribute equally to the phenotype.
F (individual genes may have different contributions to polygentic trait. one gene may have a large effect on the phenotype while other genes have smaller effects)
T/F The heritability of a single-gene trait is always 1.0
F (not always 1.0)
T/F Genetic variance for a polygenic trait is due mainly to the additive effects of dominant alleles of different genes.
F (recessive alleles)
Evidence that sleep has an inherited component is that
MZ twins share more sleep characteristics than do DZ twins
T/F DNA sequences that contribute to polygenic traits are called quantitative trait loci.
T
T/F Heritability is defined as the proportion of the phenotypic variance for a trait that is due to genetic differences in a population at a certain time.
T
T/F Polygenic traits may be influenced by the environment.
T
T/F The graph of the frequency of phenotypes in a polygenic trait has the shape of a bell curve.
T
T/F The heritability of a trait changes when the environment changes
T
For a multifactorial, polygenic trait, the characteristic shape of the mathematical plot of frequency for each phenotype class is
a bell curve
The pattern of genetic transmission typical of a multifactorial trait is
a continuous variation of phenotypic expression
Genetic contribution to intelligence increases with age because
a person has greater control over his or her environment.
a synapse is
a space between neurons
Suppose that there are three genes (called A, B, and C) that influence human skin color. (In reality, there are many more genes that affect skin color!) For each of these three genes, a dominant allele (represented by a capital letter) increases the amount of pigment production by a fixed amount. All dominant alleles have an equal effect on the phenotype. Put these genotypes in order with respect to the phenotype they produce, from lightest skin color (least pigment) to darkest skin color (most pigment).
aabbcc aaBbcc AabbCc aaBbCC AaBBCc AaBBCC AABBCC
Mendel's laws
apply to multifactorial traits but may be difficult to follow because different genes contribute in different degrees to a phenotype.
The DNA of dizygotic twins is
as alike as the DNA of any two full siblings
Multifactorial traits include
both single gene and polygenic traits.
The proportion of genes that two people with a certain relationship share is the
coefficient of relatedness
Among pairs of twins in whom at least one has a particular trait, the _____ of the trait is equal to the percentage of pairs in which both twins express the trait.
concordance
Among pairs of twins in whom at least one has a trait, the percentage of pairs in which both twins express the trait is the _____ of the trait.
concordance
If a trait has a large inherited component, then concordance among monozygotic twins will be
considerably higher than that of dizygotic twins
Polygenic traits are
determined by more than one gene
twins who differ in a trait are ____ for that trait
discordant
The chance that a polygenic multifactorial trait will occur in an individual is the ____________ .
empiric risk
Genes can affect behavior by encoding proteins that
function as neurotransmitter transporters, neurotransmitter receptors, and enzymes that control the synthesis of neurotransmitters and myelin.
For a polygenic trait with little or no environmental influence, the concordance value for monozygotic twins will be ____ the concordance value for dizygotic twins.
greater than
The proportion of phenotypic variance for a trait that is due to genetic differences in a population is the trait's
heritability
The number of new cases of a genetic disorder diagnosed per year in a population of a given size is the _____of the disorder.
incidence
Empiric risk is based on _____, which is the _____.
incidence; rate at which a certain event occurs
As individuals age, heritability of IQ
increases.
Which of the following behavioral disorders has the highest rate of prevalence in the U.S. population?
major depressive disorder
Identical twins are also called ____ twins
monozygotic
To assess the genetic component of a multifactorial trait, it would be most appropriate to study _____
monozygotic twins separated at birth
Traits that have both inherited and environmental causes are termed
multifactoral
genes control the synthesis of _____, a fatty substance that coats and insulates neurons
myelin
Neurons use chemical signals called ____ to communicate with one another.
neurotransmitters
Average height of college students increased throughout the 20th century because
nutrition improved greatly in that time
concordance refers to
percentage of twin pairs in which both express a trait among pairs in which at least one twin has the trait.
The distinction between multifactorial and polygenic traits is that
polygenic traits are caused by more than one gene, and multifactorial traits are caused by one or more genes as well as environmental influences.
During neurotransmission, the cell that synthesizes and releases the signaling molecule is called the ____ neuron.
presynaptic
The _____of a genetic disorder is the proportion of individuals in a population who have the disorder at a specific time.
prevalence
DNA sequences that contribute to polygenic traits are called
quantitative trait loci
The best description of the probable role that genes play in behavioral disorders is that
single genes with major influences as well as small inputs from common gene variants contribute to susceptibility to behavioral disorders, perhaps requiring environmental triggers.
Candidate genes for the inherited components of mood disorders affect
single transduction and neurotransmission
Associations between neurons called ____ are the site of neurotransmission.
synapses
Heritability of a trait can change because
the environment can change
heritability refers to
the genetic contribution to the variability of a phenotype in a population at a particular time.
The coefficient of relatedness indicates
the proportion of genes that types of relatives share
Causes of intellectual disability include gene and chromosomal disorders, infections, malnutrition, and noninherited birth defects.
true
A continuously varying trait is
weight in humans