GN 301 EXAM 3 UPDATED ACTUAL QUESTIONS AND
CORRECT ANSWERS
Question:
1. what are characteristics of a quantitative trait?
Answer:
range of phenotypes and the trait is controlled by more than one gene; continuous variation with no distinct
F2 classes
Question:
2. list some traits that are under quantitative control
Answer:
height, weight, hair color, eye color, skin color
Question:
3. what is East's multiple factor hypothesis?
Answer:
1. the expression of the trait depends on additive effects of a number of genes
2. the effect of each gene is small
3. the environment plays an important role in the expression of a trait (smooths curve)
Question:
4. define threshold traits
Answer:
phenotype is either healthy or disease; risk factor accumulates based on the genotype and the environment;
if risk factor exceeds a threshold, the disorder is seen
Question:
5. Assume 3 genes are responsible and a dominant allele at each locus adds 5 units of risk, but a recessive
allele at a locus only adds 2 units of risk and individuals with 25 or more units of risk develop the disorder.
What is the greatest number of risk factors with this model?
Answer:
AABBCC= 5x6= 30 units
Question:
6. Assume 3 genes are responsible and a dominant allele at each locus adds 5 units of risk, but a recessive
allele at a locus only adds 2 units of risk and individuals with 25 or more units of risk develop the disorder.
What is the lowest number of risk factors with this model?
Answer:
aabbcc= 2x6=12 units
,Question:
7. Assume 3 genes are responsible and a dominant allele at each locus adds 5 units of risk, but a recessive
allele at a locus only adds 2 units of risk and individuals with 25 or more units of risk develop the disorder.
Mate AABbCc x AABbcc.
•Do either of the parents have the disorder?
Answer:
AABbCc = (4x5) + (2x2) = 24 units AABbcc= (3x5) + (3x2) = 21 units NO
Question:
8. Assume 3 genes are responsible and a dominant allele at each locus adds 5 units of risk, but a recessive
allele at a locus only adds 2 units of risk and individuals with 25 or more units of risk develop the disorder.
Mate AABbCc x AABbcc. What is largest number of risk units possible in children? Genotype? Will they
have disorder?
Answer:
AABBCc= (5x5) + (1x2) = 27 units YES
Question:
9. What are monozygotic twins
Answer:
identical; come from single egg-sperm union whose embryo splits into 2 embryos early in development
Question:
10. What are dizygotic twins
Answer:
fraternal; 2 seperate egg-sperm unions and occur when a female ovulates 2 eggs and they are both
fertilized
Question:
11. what are super twins
Answer:
a combination of monozygotic and dizygotic progeny in a single preganancy.
Question:
12. When do most identical twins separate? How does the time of the splitting of the embryo affect
whether or not there are 2 placentas?
Answer:
1/3 separate prior to day 5 resulting in separate chorions and amnions; 2/3 split is after day 5 and before
day 9 so they share chorion but have separate amnions; fraternal twins have their own amnions and
chorions (and 1/3 identical twins)- the chorion develops into the placenta
Question:
13. explain the inheritance of twinning
Answer:
there is no evidence that monozygotic twinning is inherited; fraternal twinning is inherited and increases
with age of mother- genes for super ovulation can be passed through sons even through only females
super-ovulate; there are differences in frequencies of twinning in different geographical regions and racial
backgrounds
,Question:
14. Quantitate traits often assumed to be distributed in a ____________ distribution
Answer:
normal
Question:
15. what is heritability
Answer:
proportion of phenotypic variance due to genetic effects; 0(none due to genetics)-1(all from genetics)
Question:
16. define Vp, Vg, and Ve
Answer:
variance in phenotype, genotype, and environment
Question:
17. How do you compare genetic effects given data on different twins
Answer:
MZ raised together and DZ raised together
Question:
18. what does concordant mean
Answer:
same for trait
Question:
19. what does discordant mean
Answer:
differ to trait
Question:
20. explain concordance in twin studies
Answer:
% concordance- percentage of twins that showed the same phenotype; high MZ and low DZ=high
heritability; similar MZ and DZ=low heritability
Question:
21. what are the limitations to heritability
Answer:
DOES NOT say how much genes affect the trait (just says how much genes affect variation in trait); an
individual DOES NOT have heritability (.8 does not mean 80% is due to genes just 80% variation is
determined by genetics); SPECIFIC in a particular population and environment; ASSUMES that
environment for related is same as unrelated individuals
Question:
22. what does QTL stand for
, Answer:
Quantitative Trait Loci
Question:
23. what are commonly used markers for QTL
Answer:
SNPs (single nucleotide polymorphism) and micro satellite regions
Question:
24. what does GWAs stand for?
Answer:
Genome Wide Association Studies
Question:
25. what is the purpose of the GWAS
Answer:
1. associate a trait and gene markers in a biological population (random mating population) as opposed to
controlled crosses
2. use molecular genetic techniques to scan entire genome for regions that show statistical importance for
trait
3. allow us to identify genes associated with quantitive traits
4. genes identified in model organisms (mice, fruit flies) often are similar to genes in humans providing us
with candidate genes for human quantitative traits
Question:
26. what does the gene chip (microarray) show
Answer:
SNP probes on a chip, sample is incubated with chip and binds where SNPs match, computer determines
which SNPs are present
Question:
27. what does the manhattan plot show
Answer:
all human chromosomes along the X axis and the location of possible candidate genes on the Y axis
Question:
28. what factors are assessed in IQ tests?
Answer:
spatial visualization, ability to memorize, mathematical reasoning, inductive reasoning, verbal
comprehension, word fluency
Question:
29. how is IQ calculated
Answer:
mental age/ chronological age example: 8 year old performs at 10 year level=120
CORRECT ANSWERS
Question:
1. what are characteristics of a quantitative trait?
Answer:
range of phenotypes and the trait is controlled by more than one gene; continuous variation with no distinct
F2 classes
Question:
2. list some traits that are under quantitative control
Answer:
height, weight, hair color, eye color, skin color
Question:
3. what is East's multiple factor hypothesis?
Answer:
1. the expression of the trait depends on additive effects of a number of genes
2. the effect of each gene is small
3. the environment plays an important role in the expression of a trait (smooths curve)
Question:
4. define threshold traits
Answer:
phenotype is either healthy or disease; risk factor accumulates based on the genotype and the environment;
if risk factor exceeds a threshold, the disorder is seen
Question:
5. Assume 3 genes are responsible and a dominant allele at each locus adds 5 units of risk, but a recessive
allele at a locus only adds 2 units of risk and individuals with 25 or more units of risk develop the disorder.
What is the greatest number of risk factors with this model?
Answer:
AABBCC= 5x6= 30 units
Question:
6. Assume 3 genes are responsible and a dominant allele at each locus adds 5 units of risk, but a recessive
allele at a locus only adds 2 units of risk and individuals with 25 or more units of risk develop the disorder.
What is the lowest number of risk factors with this model?
Answer:
aabbcc= 2x6=12 units
,Question:
7. Assume 3 genes are responsible and a dominant allele at each locus adds 5 units of risk, but a recessive
allele at a locus only adds 2 units of risk and individuals with 25 or more units of risk develop the disorder.
Mate AABbCc x AABbcc.
•Do either of the parents have the disorder?
Answer:
AABbCc = (4x5) + (2x2) = 24 units AABbcc= (3x5) + (3x2) = 21 units NO
Question:
8. Assume 3 genes are responsible and a dominant allele at each locus adds 5 units of risk, but a recessive
allele at a locus only adds 2 units of risk and individuals with 25 or more units of risk develop the disorder.
Mate AABbCc x AABbcc. What is largest number of risk units possible in children? Genotype? Will they
have disorder?
Answer:
AABBCc= (5x5) + (1x2) = 27 units YES
Question:
9. What are monozygotic twins
Answer:
identical; come from single egg-sperm union whose embryo splits into 2 embryos early in development
Question:
10. What are dizygotic twins
Answer:
fraternal; 2 seperate egg-sperm unions and occur when a female ovulates 2 eggs and they are both
fertilized
Question:
11. what are super twins
Answer:
a combination of monozygotic and dizygotic progeny in a single preganancy.
Question:
12. When do most identical twins separate? How does the time of the splitting of the embryo affect
whether or not there are 2 placentas?
Answer:
1/3 separate prior to day 5 resulting in separate chorions and amnions; 2/3 split is after day 5 and before
day 9 so they share chorion but have separate amnions; fraternal twins have their own amnions and
chorions (and 1/3 identical twins)- the chorion develops into the placenta
Question:
13. explain the inheritance of twinning
Answer:
there is no evidence that monozygotic twinning is inherited; fraternal twinning is inherited and increases
with age of mother- genes for super ovulation can be passed through sons even through only females
super-ovulate; there are differences in frequencies of twinning in different geographical regions and racial
backgrounds
,Question:
14. Quantitate traits often assumed to be distributed in a ____________ distribution
Answer:
normal
Question:
15. what is heritability
Answer:
proportion of phenotypic variance due to genetic effects; 0(none due to genetics)-1(all from genetics)
Question:
16. define Vp, Vg, and Ve
Answer:
variance in phenotype, genotype, and environment
Question:
17. How do you compare genetic effects given data on different twins
Answer:
MZ raised together and DZ raised together
Question:
18. what does concordant mean
Answer:
same for trait
Question:
19. what does discordant mean
Answer:
differ to trait
Question:
20. explain concordance in twin studies
Answer:
% concordance- percentage of twins that showed the same phenotype; high MZ and low DZ=high
heritability; similar MZ and DZ=low heritability
Question:
21. what are the limitations to heritability
Answer:
DOES NOT say how much genes affect the trait (just says how much genes affect variation in trait); an
individual DOES NOT have heritability (.8 does not mean 80% is due to genes just 80% variation is
determined by genetics); SPECIFIC in a particular population and environment; ASSUMES that
environment for related is same as unrelated individuals
Question:
22. what does QTL stand for
, Answer:
Quantitative Trait Loci
Question:
23. what are commonly used markers for QTL
Answer:
SNPs (single nucleotide polymorphism) and micro satellite regions
Question:
24. what does GWAs stand for?
Answer:
Genome Wide Association Studies
Question:
25. what is the purpose of the GWAS
Answer:
1. associate a trait and gene markers in a biological population (random mating population) as opposed to
controlled crosses
2. use molecular genetic techniques to scan entire genome for regions that show statistical importance for
trait
3. allow us to identify genes associated with quantitive traits
4. genes identified in model organisms (mice, fruit flies) often are similar to genes in humans providing us
with candidate genes for human quantitative traits
Question:
26. what does the gene chip (microarray) show
Answer:
SNP probes on a chip, sample is incubated with chip and binds where SNPs match, computer determines
which SNPs are present
Question:
27. what does the manhattan plot show
Answer:
all human chromosomes along the X axis and the location of possible candidate genes on the Y axis
Question:
28. what factors are assessed in IQ tests?
Answer:
spatial visualization, ability to memorize, mathematical reasoning, inductive reasoning, verbal
comprehension, word fluency
Question:
29. how is IQ calculated
Answer:
mental age/ chronological age example: 8 year old performs at 10 year level=120
