Chapter 7 Lecture Guide

Chapter 7: Multifactorial Traits Lecture Guide
Genes & the Environment
• Few, if any genes act _____________________
• Environmental factors and other genes may
_________________ the expression of certain genes
• Traits can be described as either __________________
– Single gene traits- reflects the activities of _______
– Polygenic- reflects the activities of _____________
_________ gene
• Both single genes and polygenic traits are considered to be
_____________________________ due to having an
interaction between their ______________ and the
– Example- lung cancer
– Can be caused by defective genes AND
environmental factors such as smoking or pollution
• Single gene traits are said to be discrete or qualitative in
that the traits are either expressed or not expressed
– Follows the “all or none” effect
Polygenic Traits
• Polygenic traits produce a continuously
________________ phenotype
– Also called ________________________________
– DNA sequences involved are referred to as
quantitative trait loci (QTLs)
• Not many polygenic traits are purely polygenic due to
environmental factors
– Examples include
– Height
– Skin color
– Body weight
– Behavioral traits
– Fingerprint patterns
• Follow Mendelian laws but are more difficult to predict due
to combined actions of genes and the environmental
• The effect of genes is additive
– The input of genes is not identical for all
• The frequency of distribution of phenotypes forms a
Fingerprint Patterns
• Skin on fingertips is folded into patterns of raised skin
called _________________________ that form loops,
whorls, and arches
– Makes a _______________________
The number of ridges is determined by genes and the
– During weeks _____________ of prenatal
development, ridges can be altered as the tips of the
fingers and toes touch the amniotic sac
___________________________ can be used to compare
the number of ridges that comprise these fingerprint
patterns to identify and distinguish individuals
– Is important in genetics because some genetic
disorders have unusual ridge patterns
Total ridge count can be used to quantify fingerprints
– Males have 145 while females have 126
• Effect of the __________________________ on height is
obvious due to the fact that people who do not eat enough
do not reach their genetic potential for height
• Studies have identified ______ genes that affect height
• SNP patterns are also seen in individuals with periods of
rapid height increase
Skin Color
• More than _______ genes affect pigmentation in skin, hair,
and the irises of the eyes
• Melanin pigments color the skin to different degrees in
different individuals
– Melanin produced by ______________________
which are packaged into _____________________
• Function of melanin is to protect again __________
_____________ from UV radiation while exposure to
the sun increases melanin synthesis
– All humans have the ________ number of
melanocytes – the melanosome number, size, and
density is what ___________ per person
• Skin color is one physical trait that is used to distinguish
– The definition of race based largely on skin color is a
social construct more than a biological concept
– In genetics, races are groups within ____________
that are distinguished by different _____________
• Skin color is NOT a reliable indicator of ancestry
– 93% of varying inherited traits are no more common in
people of one skin color than any other
Body Weight
• Is a multifactorial trait that reflects ________________
• 30% of all adults in the US are obese, and another 35%
are overweight
Scientific studies use body mass index (BMI) to determine
– BMI= weight (kg)/ height 2 (m2)
Lifestyle (diet and exercise) are environmental components
that impact body weight
Genes do influence hunger and metabolism
– More than _________ genome regions have been
found to harbor genes that affect how much we eat,
how we use calories, and how fat is distributed in the
Investigating Multifactorial Traits
• Using Mendel’s laws it is possible to predict the risk that a
single gene trait will recur in a family from knowing its
mode of inheritance
• Predicting recurring risks for polygenic traits is more
challenging than single gene traits
Empiric Risk
• To predict the chance of that a polygenic trait will occur, the
________________________ is determined
– Is based on _________________________
– Is the rate at which a certain event occurs
– Empiric risk __________________ with the severity of
the disorder, the number of affected family members,
and how closely related a person is to the affected
– Is also based on _____________________ which is
the proportion of individuals who have a particular trait
at a specific time
• An example of empiric risk lies with neural tube defect
– In the US, the empiric risk of carrying a fetus with NTD
is 1:1000
– For England, Ireland, and Scotland the empiric risk is
– The risk of recurrence increases to3% for all ethnic
groups if one sibling already had NTD and increases
even more if more than one sibling has it
– Example- Cleft Lip
Environmental Influences
• _______________________ of traits does exist and are
due in part to inborn differences within populations along
with environmental influences
• Heritability can estimate the proportion of the
_________________________________ for a trait that is
due to genetic differences in a certain population at a
certain time
– Heritability equals 1.0 for a trait whose variability is
completely the result of gene action
• Heritability is different from empiric risk in that empiric risk
is due to _______________________ influences while
heritability focuses on _____________________
• Heritability changes as the _______________________
– Example- skin color
– Heritability can be higher or lower due to location
• More melanin production= darker skin
• Less melanin production= lighter skin
• Researchers use several statistical methods to estimate
• One way is to compare the proportion of people sharing a
trait to the proportion predicted to share the trait
• The expected proportion is derived by knowing the
__________________ relationships of the individuals
along with the _________________________________
– Is the proportion of _______________ shared between
two people related in a certain way
Adopted Individuals
• Similarities between adopted people and adopted parents
reflect mostly __________________________ influences
• Similarities between adoptees and their biological parents
reflect mostly __________________________ influences
• Therefore, information on both sets of parents can reveal
how heredity and the environment both contribute to a trait
• Twin studies have largely replaced adoption methods
• __________________________ measures the frequency
of expression of a trait in both members of monozygotic
(MZ) or dizygotic (DZ) twins
– Twins who differ in a trait are said to be discordant for
• For a trait largely determined by genes, concordance is
higher for MZ than DZ twins
• Dizygotic twins = Shared environment and 50% of
• Monozygotic twins = Identical genotype and shared
• Twins raised apart = Shared genotype but not
• Adopted individuals = Shared environment but not
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