1
(GN verified)
GN 301 EXAM 3 REVIEW NOTES | COMPREHENSIVE
STUDY GUIDE
What are "Super Twins"?
having a combination of identical and fraternal twins in one pregnancy
What are some genetic causes of intellectual disability?
Single gene examples (Simple Mendelian) PKU (autosomal
recessive)Galactosemia (autosomal recessive)Hurler Syndrome (autosomal
recessive)Tay-Sachs Disease (autosomal recessive)Rett Syndrome (X-linked
dominant) Polygenic: Possible to get the "bad luck" alleles of several polygenes
that contribute to intelligence See familial inheritance patterns of some intellectual
disabilitiesMore than 75% of cases come from less than 10% of familiesIf both
parents have IQ values in the 50 - 70 range, there is a 60-70% chance that their
child will also have a subnormal intelligence
Approximately ____% of the US population is intellectually disabled.
3
What is the genetic basis of each of the following disorders? Down Syndrome, Rett
Syndrome, Fragile X Syndrome, Williams Syndrome, Patau Syndrome, Edward
Syndrome, Galactosemia, PKU, Hurler Syndrome, Tay Sachs
Down Syndrome: trisomy 21Rett Syndrome: X-linked dominantFragile X
Syndrome: X-linked dominantWilliams Syndrome: autosomal dominantPatau
Syndrome: trisomy 13Edward Syndrome: trisomy 18Galactosemia: autosomal
recessivePKU: autosomal recessiveHurler Syndrome: autosomal recessiveTay
Sachs: autosomal recessive
Intellectual disabilities can have several causes: Give the name of a genetic
disorder that causes intellectual disabilities and is inherited in each of the manners
below: Trisomic, autosomal recessive, X linked, Deletion
Trisomic: Down Syndrome, Patau Syndrome, Edward Syndrome Autosomal
recessive: Galactosemia, PKU, Hurler Syndrome, Tay Sachs X-linked: Fragile X
Syndrome (dominant), colorblindness Deletion: Cri du chat, Wolf-Hirschhorn,
Angelman Syndrome
, 2
(GN verified)
In order to be considered to be intellectually disabled, an individual's IQ is less
than ______.
70
Which type of twinning is more likely to run in families? Why?
There is evidence that fraternal twinning is inherited. There are differences in
fraternal twin rates in different geographical regions and among different racial
groups. The frequency also increases with an increase in maternal age.
Define heritability, concordance, concordant, discordant, correlation
Heritability: the proportion of phenotypic variance that is due to genetic effects
Concordance: the probability that a pair of individuals will both have a certain
characteristic given that one of the pair has the characteristic Concordant: if twins
same for a trait Discordant: if twins differ for a trait Correlation: the proportion of
variance that two traits share due to genetic causes, the correlation between the
genetic influences on a trait and the genetic influences on a different trait
estimating the degree of pleiotropy or causal overlap
Be able to compare values of MZ:DZ concordance ratios to determine which trait
has a higher heritability
If the MZ and DZ values are similar, most of the variation in phenotype is due to
variance in environmental effects which indicates a low heritability.If there is a
low MZ value but it is still quite higher than the DZ value, there is a genetic
predisposition, but a low to moderate heritability for the trait.High MZ: Low DZ
indicates significant role of the variance of genetic effects in the phenotypic
varianceSimilar MZ and DZ indicates a lot of variation is due to variance in
environmental effectsLow MZ but still much higher than DZ indicates genetic
predisposition, but variance due to environmental factors is important in the
variance of the phenotypes for this trait
What is a threshold trait?
A threshold trait refers to a trait that only becomes apparent when a certain
threshold of intensity is reached.
Use the idea of the additive effects of alleles to determine whether an individual of
a particular genotype has a genetic disorder
, 3
(GN verified)
In these situations, risk factors accumulate based on the genotype and the
environment. If the risk factors exceed a threshold, the disorder is seen.
Which trait is expected to have a higher heritability based on the MZ:DZ ratios
given? Trait A 95:85 or Trait B 95:4
Trait B High MZ: Low DZ indicates significant role of the variance of genetic
effects in the phenotypic variance
The expression of quantitative characteristics depends on the genotype and ______
the environment
How are twin studies used to help us understand the heritability of quantitative
characteristics?
Twin studies are studies conducted on identical or fraternal twins. They aim to
reveal the importance of environmental and genetic influences for traits,
phenotypes, and disorders.
In order to evaluate the genetic contribution of a characteristic, is it best to
compare which of the following 2 types of twins? MZ reared together, MZ reared
apart, DZ reared together, DZ reared apart
Compare MZ raised together and DZ raised together to estimate genetic effects
Which 2 (of the above) should be compared to evaluate the environmental
contribution to a trait?
Compare MZ raised apart and DZ raised apart to estimate genetic effects
What do the abbreviations QTL and GWAS stand for?
QTL stands for Quantitative Trait Loci GWAS stands for Genome Wide
Association Studies
What is the purpose of a GWAS experiment?
Allow us to identify genes that are associated with quantitative traits.
The average IQ value (based on IQ tests) is set at _____
100
What are some environmental factors that can lead to intellectual disabilities?
(GN verified)
GN 301 EXAM 3 REVIEW NOTES | COMPREHENSIVE
STUDY GUIDE
What are "Super Twins"?
having a combination of identical and fraternal twins in one pregnancy
What are some genetic causes of intellectual disability?
Single gene examples (Simple Mendelian) PKU (autosomal
recessive)Galactosemia (autosomal recessive)Hurler Syndrome (autosomal
recessive)Tay-Sachs Disease (autosomal recessive)Rett Syndrome (X-linked
dominant) Polygenic: Possible to get the "bad luck" alleles of several polygenes
that contribute to intelligence See familial inheritance patterns of some intellectual
disabilitiesMore than 75% of cases come from less than 10% of familiesIf both
parents have IQ values in the 50 - 70 range, there is a 60-70% chance that their
child will also have a subnormal intelligence
Approximately ____% of the US population is intellectually disabled.
3
What is the genetic basis of each of the following disorders? Down Syndrome, Rett
Syndrome, Fragile X Syndrome, Williams Syndrome, Patau Syndrome, Edward
Syndrome, Galactosemia, PKU, Hurler Syndrome, Tay Sachs
Down Syndrome: trisomy 21Rett Syndrome: X-linked dominantFragile X
Syndrome: X-linked dominantWilliams Syndrome: autosomal dominantPatau
Syndrome: trisomy 13Edward Syndrome: trisomy 18Galactosemia: autosomal
recessivePKU: autosomal recessiveHurler Syndrome: autosomal recessiveTay
Sachs: autosomal recessive
Intellectual disabilities can have several causes: Give the name of a genetic
disorder that causes intellectual disabilities and is inherited in each of the manners
below: Trisomic, autosomal recessive, X linked, Deletion
Trisomic: Down Syndrome, Patau Syndrome, Edward Syndrome Autosomal
recessive: Galactosemia, PKU, Hurler Syndrome, Tay Sachs X-linked: Fragile X
Syndrome (dominant), colorblindness Deletion: Cri du chat, Wolf-Hirschhorn,
Angelman Syndrome
, 2
(GN verified)
In order to be considered to be intellectually disabled, an individual's IQ is less
than ______.
70
Which type of twinning is more likely to run in families? Why?
There is evidence that fraternal twinning is inherited. There are differences in
fraternal twin rates in different geographical regions and among different racial
groups. The frequency also increases with an increase in maternal age.
Define heritability, concordance, concordant, discordant, correlation
Heritability: the proportion of phenotypic variance that is due to genetic effects
Concordance: the probability that a pair of individuals will both have a certain
characteristic given that one of the pair has the characteristic Concordant: if twins
same for a trait Discordant: if twins differ for a trait Correlation: the proportion of
variance that two traits share due to genetic causes, the correlation between the
genetic influences on a trait and the genetic influences on a different trait
estimating the degree of pleiotropy or causal overlap
Be able to compare values of MZ:DZ concordance ratios to determine which trait
has a higher heritability
If the MZ and DZ values are similar, most of the variation in phenotype is due to
variance in environmental effects which indicates a low heritability.If there is a
low MZ value but it is still quite higher than the DZ value, there is a genetic
predisposition, but a low to moderate heritability for the trait.High MZ: Low DZ
indicates significant role of the variance of genetic effects in the phenotypic
varianceSimilar MZ and DZ indicates a lot of variation is due to variance in
environmental effectsLow MZ but still much higher than DZ indicates genetic
predisposition, but variance due to environmental factors is important in the
variance of the phenotypes for this trait
What is a threshold trait?
A threshold trait refers to a trait that only becomes apparent when a certain
threshold of intensity is reached.
Use the idea of the additive effects of alleles to determine whether an individual of
a particular genotype has a genetic disorder
, 3
(GN verified)
In these situations, risk factors accumulate based on the genotype and the
environment. If the risk factors exceed a threshold, the disorder is seen.
Which trait is expected to have a higher heritability based on the MZ:DZ ratios
given? Trait A 95:85 or Trait B 95:4
Trait B High MZ: Low DZ indicates significant role of the variance of genetic
effects in the phenotypic variance
The expression of quantitative characteristics depends on the genotype and ______
the environment
How are twin studies used to help us understand the heritability of quantitative
characteristics?
Twin studies are studies conducted on identical or fraternal twins. They aim to
reveal the importance of environmental and genetic influences for traits,
phenotypes, and disorders.
In order to evaluate the genetic contribution of a characteristic, is it best to
compare which of the following 2 types of twins? MZ reared together, MZ reared
apart, DZ reared together, DZ reared apart
Compare MZ raised together and DZ raised together to estimate genetic effects
Which 2 (of the above) should be compared to evaluate the environmental
contribution to a trait?
Compare MZ raised apart and DZ raised apart to estimate genetic effects
What do the abbreviations QTL and GWAS stand for?
QTL stands for Quantitative Trait Loci GWAS stands for Genome Wide
Association Studies
What is the purpose of a GWAS experiment?
Allow us to identify genes that are associated with quantitative traits.
The average IQ value (based on IQ tests) is set at _____
100
What are some environmental factors that can lead to intellectual disabilities?
