MOD 6: Multifactorial Traits & Behavior

Question 1

means that many factors are involved in causing
certain health problems or disorders. A combination of genes from both parents plus unknown environmental
factors make the trait or condition.

Answer 1

Multifactorial inheritance

Question 2

However, many traits of importance in plant breeding, animal breeding, and medical genetics are influenced by
multiple genes. These are known as _______________ because of the multiple genetic and environmental
factors implicated in their causation.

Answer 2

multifactorial traits

Question 3

T or F
A trait can either be single-gene (or Mendelian or
monogenic) or polygenic. Both Mendelian and polygenic
traits can be multifactorial, meaning they are influenced by
the environment.

Answer 3

T

Question 4

– is defined as a trait that reflects the
activities of more than one gene

Answer 4

POLYGENIC TRAIT

Question 5

–
those not influenced by the environment – are very rare.

Answer 5

Pure polygenic traits

Question 6

Polygenic multifactorial traits include common ones like:

Answer 6

height, skin color, body weight, many illnesses, behavioral
conditions and tendencies.

Question 7

where 3 genes contribute to the risk of developing this disease but other genes may exert smaller effects.

Answer 7

Type II Diabetes Mellitus

Question 8

– where studies show that a gene on chromosome 1 contributes sensitivity to sound; a gene on
chromosome 5 produces the pulsating headache and sensitivity to light; a gene on chromosome 8 is associated
with nausea and vomiting.

Answer 8

Migraine

Question 9

L reflect additive contributions of several genes where each gene confers a
degree of susceptibility, but the input of these genes is not necessarily equal.

Answer 9

Polygenic multifactorial conditions

Question 10

some examples of polygenic multifactorial conditions

Answer 10

• Type 2 Diabetes Mellitus
• Migraine

Question 11

T or F
The chance of a multifactorial trait or condition happening to a person depends on how closely the family
member with the trait is related to the person involved.

Answer 11

T

Question 12

DNA sequences that contribute to polygenic traits are
called _____________.

Answer 12

quantitative trait loci (QTLs).

Question 13

The combined action of many genes for a polygenic trait often produces a “shade of grey” or “continuously
varying” phenotype which is called as _________

Answer 13

quantitative trait

Question 14

T or F
A multifactorial trait is continuously varying if it is also polygenic. The individual genes that confer a polygenic trait
follow Mendel’s laws, but together they do not produce single0gene phenotypic ratios. They all contribute to the
phenotype, but without being dominant or recessive to each other

Answer 14

T

Question 15

T or F
Single-gene traits are instead discrete or
quantitative, often providing an “all-or-none” phenotype such as “normal” versus “affected”.

Answer 15

F
Single-gene traits are instead discrete or
qualitative, often providing an “all-or-none” phenotype such as “normal” versus “affected”.

Question 16

Although the expression of a polygenic trait is continuous, we can categorize individuals into classes, calculate the
frequencies of the classes, plot the frequency for each phenotype class to yield a _____________ result. Even
when different numbers of genes affect the trait, the curve takes the same shape.

Answer 16

bell-shaped curve

Question 17

FINGERPRINT PATTERNS – the skin on the fingertips is folded into patterns of raised skin called __________ that
align to form loops, whorls and arches

Answer 17

dermal ridges

Question 18

________________ compares the number of ridges that comprise these patterns to identify and distinguish individuals

This technique is part of genetics because certain disorders such as Down syndrome include unusual
ridge patterns. To quantify a fingerprint, a
total ridge count is done which are then plotted on a bar graph revealing an approximate bell-shaped curve of a continuously varying trait.

Answer 18

Dermatoglyphics or skin
writing

Question 19

is also an application of dermatoglyphics.

Answer 19

Forensic fingerprint analysis

Question 20

T or F

HEIGHT – the effect of the environment on height is obvious – people who do not eat enough do not reach
their genetic potential for height. Studies have also shown that people raised from different decades have varying height ranges and this difference can be attributed to improved diet and better
overall health.

Answer 20

T

Question 21

Genome-wide association studies have identified dozens of genes that affect height by
comparing __________.

Answer 21

genetic markers

Question 22

SKIN COLOR – ________ is the pigment responsible for giving color to the skin to different degrees in different
individuals. Scientists have detected more than 100 genes that affect pigmentation in skin, hair and irises.
It protects against DNA damage from ultraviolet radiation, and exposure to the sun increases melanin synthesis.

Answer 22

Melanin

Question 23

T or F
Although people come in different shades, we all have about the same number of
melanocytes per unit area of skin but differ in melanosome number, size and density of distribution.
Differences in skin color arise from the number and distribution of melanin pieces in the skin cells in the
uppermost layers

Answer 23

T

Question 24

– a traditional approach which is based on incidence in a specific population. Geneticists use
this approach to predict the chance that a polygenic multifactorial trait will occur in a particular individual.
Empiric risk is not a calculation, but a population statistic based on observation

Answer 24

EMPIRIC RISK

Question 25

is the rate at which a certain event occurs, such as the number of new cases of a particular disorder
diagnosed per year in a population of known size.

Answer 25

Incidence

Question 26

is the proportion or number of individuals in a population who have a particular disorder at a
specific time, such as during one year.

Answer 26

Prevalence

Question 27

T or F
Empiric risk decreases with the severity of the disorder, the # of affected family members, and how closely related a person is to the affected individuals. If a trait has an inherited component, then it makes sense that the closer the relationship between two individuals, one of whom has the trait, the greater the probability that
the second individual has the trait, too, because they have more genes in common

Answer 27

F

Empiric risk increases with the severity of the disorder, the # of affected family members, and how closely
related a person is to the affected individuals. If a trait has an inherited component, then it makes sense that
the closer the relationship between two individuals, one of whom has the trait, the greater the probability that
the second individual has the trait, too, because they have more genes in common

Question 28

Since empiric risk is based solely on observation, this approach can be used to derive disorders with vague
transmission patterns. An example is _______________, an overgrowth of muscle between the stomach and
small intestine, which must be surgically corrected shortly after birth, or the newborn will be unable to digest foods.

Answer 28

Pyloric stenosis

Question 29

– is an approach which estimates the proportion of the phenotypic variation for a particular trait that is due to genetic differences in a certain population at a certain time. If empiric risk could result from non-genetic influences, then __________ focuses on the genetic component of the variation in a trait.

Answer 29

HERITABILITY,heritability

Question 30

One way to estimate heritability is to compare the actual proportion of pairs of people related in a certain
manner who share a particular trait, to the expected proportion of pairs that would share it if were inherited in
a Mendelian fashion. The expected proportion is derived by knowing the blood relationships of the individuals
and using _________________, which is the proportion of genes that two people related in a certain way
share

Answer 30

coefficient of relatedness

Question 31

TWINS – the genomes of identical twins are not really identical – they differ in DNA sequences called ________________ which are repeats of short sequences.

Answer 31

copy number variants (CNVs)

Question 32

People differ in the number of repeats. A trait that occurs more frequently in both members of identical or _____________ twin pairs than in both members of fraternal or_____________ twin pairs are at least partly controlled by heredity.

Answer 32

identical - (monozygotic or MZ)
Fraternal (dizygotic or DZ)

Question 33

Geneticists calculate the _____________
of a trait as the percentage of pairs in
which both twins express the trait
among pairs of twins in whom at least one has the trait. Twins who differ in a trait are said to be discordant for it.

Answer 33

concordance

Question 34

_____________ is any study of genetic variation across the entire
human genome that is
designed to identify the genetic associations
with observable traits, or the presence or
absence of a disease or condition, as according to the National Institutes of Health (NIH).

Answer 34

Genome-Wide Association Studies

Question 35

Genome-wide association studies seek DNA _____________ that are shared with much greater frequency among individuals with the same illness or trait than among others.

Answer 35

sequence variants

Question 36

2 eggs + 2 sperm

Answer 36

Fraternal twins

Question 37

1 egg + 2 sperm

Answer 37

Semi-identical twins

Question 38

1egg + 1 sperm split into 2

Answer 38

Identical twins

Question 39

Several different study designs are used in
these investigations and they include the following

Answer 39

Cohort study
Case control study
Homozygosity mapping

Question 40

– a study wherein each individual in one group is matched to an individual in another
group who shares as many characteristics as possible, such as age, sex, activity level, and environmental
exposures. SNP differences are then associated with the presence or absence of the disorder.

Answer 40

CASE-CONTROL STUDY

Question 41

– is a variation on the affected sibling pair strategy which is performed in families
that are consanguineous. The genomes of these children have more homozygous regions than do other
children, thus having a greater likelihood that they will inherit two copies of a susceptibility or disease-causing
mutation. Homozygosity mapping was used to identify genes that cause autism

Answer 41

HOMOZYGOSITY MAPPING

Question 42

– a study conducted by researchers where they follow a large group of individuals over time
and measure many aspects of their health. The most famous of which is the Framingham Heart Study, which
began tracking thousands of people and their descendants in Massachusetts in 1968.

Answer 42

COHORT STUDY

Question 43

LIMITATIONS OF GENOME-WIDE ASSOCIATION STUDIES

Answer 43

Prone to error because they include so many data points
 They reveal associations between two types of information, and not causes.
o An association only means that one event or characteristic occurs when another occurs.
o A correlation is a directional association where if one measurement increases, so does the other.
 How the patient population is selected can introduce bias to the study.
 Individuals in the control population might not actually be healthy or might have problems other than the
one being investigated.
 Genetic heterogeneity, in which different genes cause the same trait or condition, could also be a source
of error.
 They miss extremely rare SNPs or the people who share symptoms and a SNP pattern may share
something else that accounts for the association such as environmental exposure.

Question 44

frequently called SNPs (pronounced “snips”), are the most common type of genetic variation among people.

Answer 44

Single nucleotide polymorphisms,

Question 45

T or F
Unlike rare genetic disorders, body weight is a multifactorial trait that we all have. Surprisingly, many genes
affect body weight.

Answer 45

T

Question 46

Scientists use ____________ which is weight in proportion to height as a tool for measurement.
Heritability for BMI is 0.55, which leaves room for environmental influences on our appetites and sizes. Some genes implicated in determining body weight have been known through genome-wide association studies

Answer 46

body mass index (BMI)

Question 47

– is a protein hormone found in mice and humans which stimulates cells in hypothalamus to
decrease appetite and metabolize nutrients. Several studies were done wherein obese people were given
leptin, assuming they had a leptin deficiency, to trick them into feeling full. Only a small % of the
participants lost weight but the majority did not because they had leptin resistance.

Answer 47

LEPTIN

Question 48

– is a peptide hormone produced in the stomach that responds to hunger, signaling the
hypothalamus to produce more of the appetite accelerator. A drug has already been developed to block
the effects of this hormone.

Answer 48

GHRELIN

Question 49

T or F
Genes contribute to how we respond to environmental stimuli and therefore affect behavior, which includes
mood, emotion, intelligence, and personality. Candidate genes for behavioral traits and disorders affect
neurotransmission and signal transduction. Analyzing behaviors is difficult because symptoms of different syndromes overlap, study participants can provide biased information, and behaviors can be imitated.
Genetic subtypes of behavioral disorders may alter standard psychiatric diagnoses.

Answer 49

T

Question 50

Genes and Behavioural Disorder

Answer 50

Eating Disorder
Sleep
Mood disorder
Intelligence
Drug addiction
Schizophrenia
Autism

Question 51

 Eating disorders affect both sexes and are prevalent in the whole world. Twin studies indicate high
heritability.
 Candidate genes for eating disorders include protein products that control appetite & the
neurotransmitters dopamine & serotonin.

Answer 51

EATING DISORDERS:

Question 52

 Twin studies and single-gene disorders that affect the sleep-wake cycle reveal a large inherited
component to sleep behavior. A single gene causes narcolepsy both in dogs and humans.
 A large family with familial advanced sleep phase syndrome enabled researchers to identify the first
“clock” gene in humans. The period gene enables a person to respond to day & night environmental cues.

Answer 52

SLEEP:

Question 53

 Intelligence is difficult to define and measure. The general intelligence (g) value measures the inherited
portion of IQ that may underlie population variance in IQ test performance.
 Heritability for intelligence increases with age, suggesting that environmental factors are more important
early in life. Individual genes affect intelligence.
 Many chromosomal disorders affect intelligence, suggesting high heritability.

Answer 53

INTELLIGENCE:

Question 54

 Drug addiction arises from tolerance and dependence. Addiction produces stable changes in certain parts
of the brain. Structures in the limbic system are directly involved in drug addiction.
 Proteins involved in drug addiction affect neurotransmission and signal transduction.
 Candidate genes for drug addiction include dopamine D(2) receptor & variants in nicotinic receptor parts.
Nicotine binds to a receptor that normally binds acetylcholine, causing dopamine release & pleasure

Answer 54

DRUG ADDICTION:

Question 55

 Schizophrenia greatly disrupts the ability to think and perceive the world, causing delusions and
hallucinations. Onset is typically in early adulthood, and the course is episodic or steady.
 Empiric risk estimates and heritability indicate a large genetic component. Moreover, studies have
implicated several candidate genes and chromosomal regions as possible causes.
 A possible environmental influence may be prenatal exposure to the maternal immune system’s
response to influenza.

Answer 55

SCHIZOPHRENIA:

Question 56

 Major depressive disorders are relatively common and associated with deficits of serotonin and
norepinephrine, or both.
 Bipolar disorder is depressive periods and periods of mania or hypomania. Hundreds of genes may raise
the risk of developing this disorder. Different families have different combinations of these gene variants,
some of which, under certain environmental conditions, can lead to the disorder.
 Bipolar disorder is associated with several chromosomal sites, and its genetic roots are difficult to isolate

Answer 56

MOOD DISORDERS:

Question 57

 Autism is a loss of language, communication, and social skills beginning in early childhood. Seizures and
mental retardation may occur.
 Neuroligins and neurexins are types of proteins embedded in the cell membranes of certain brain
neurons that join across synapses, permitting neural connections to form in response to environmental
stimuli. These proteins are abnormal in some cases of autism which may explain how the condition
arises from failure of synapses to form that enable a child to integrate experiences.

Answer 57

AUTISM: