Transcript Polygenic Traits

Traits caused by multiple factors
January 2009
Polygenic and multifactorial traits
The Scottish Crop Research Institute is conducting research on
potato texture. You work at this company and need to figure out
how many genes are important for potato texture.
You cross a true-breeding potato with the roughest texture to a
true-breeding potato with the smoothest texture and then self
the F1 progeny. When you examine the F2 potatoes you
discover 7 phenotypic classes of potato texture. How many
genes determine texture in potatoes?
A. 1
B. 2
C. 3
D. 4
E. 5
During Wednesday’s snow storm you noticed individuals
wandering around campus in shorts and sandals.
Despite your alarm, you consider the possibility that cold
insensitivity is genetically determined. You spend some time
counting the frequency of these extremely cold- insensitive
individuals. You find that they occur at a frequency of 1 in
256 people. Using an additive allele model, how many
genes control cold-insensitivity?
A.
1
B.
2
C.
3
D.
4
E.
5
Question: You’ve been sent into a corn field
to examine cob size. After measuring
hundreds of cobs, you determine that there
a 9 phenotypic classes. How many genes
contribute to this quantitative trait?
A. 1
B. 2
C. 3
D. 4
E. 5
How often (on average) would you encounter
a cob in the shortest size class?
A. 1/16
B. 1/64
C. 1/256
D. 1/512
Heritability
The same inbred group of chickens
Free-range
# eggs
Barn-raised
# eggs
Egg size
Egg size
Heritability of a trait is the relative amount of phenotypic variance that is due
to genetic variance.
In which case is heritability larger?
A.
B.
free-range
Barn-raised
You have the same inbred group of chickens and you raise
them in 2 different conditions
Barn
Free-range
# eggs
# eggs
Egg size
Egg size
Heritability of a trait is the relative amount of
phenotypic variance that is due to genetic variance.
In which case is heritability larger?
A. Free-range
B. Barn
C. The heritability is equal in both conditions
D. Cannot be determined
You have the same inbred group of tomato plants and you
raise them in 2 different conditions
Field
Greenhouse
# eggs
# eggs
Fruit size
Fruit size
Heritability of a trait is the relative amount of
phenotypic variance that is due to genetic variance.
In which case is heritability smaller?
A. Greenhouse
B. Field
C. The heritability is equal in both conditions
D. Cannot be determined
While all tumors involve the accumulation of mutations, it is not clear
for several tumor types if there is a heritable genetic component to
tumor development. One such tumor is found in the adrenal
gland.
You study adrenal gland tumors in twins (both identical and fraternal)
raised in the same environment and find that identical twins are
significantly more likely to both have adrenal gland tumors when
compared with fraternal twins (typically 1 sibling has a tumor and
the other does not). Which of the following statements is a
reasonable conclusion from this result?
A.
B.
C.
D.
Adrenal glad tumors are primarily caused by environmental factors
Adrenal glad tumors are primarily caused by genetic factors
Adrenal glad tumors are caused by an equivalent amount of
environmental and genetic factors
Adrenal glad tumors are not caused by environmental or genetic
factors
You think genes contribute to cocaine abuse, so you compare abusers of cocaine
to their monozygotic twins, dizygotic twins, full siblings, and adopted siblings. If
genes contribute to the tendency for cocaine abuse, then which of the following
statements is false?
A. Dizygotic twins and siblings will share the cocaine abuse trait at approximately
equal rates
B. Monozygotic twins will be more likely to share the cocaine abuse trait when
compared to siblings
C. Siblings will be more likely to share the cocaine abuse trait when compared to
adopted siblings
D. Monozygotic twins and dizygotic twins will share the cocaine abuse trait at
approximately equal rates
QTL Mapping
You are interested in studying obesity. You have found a large
number of obese people and have determined the alleles of
many, many molecular markers that they carry on each
chromosome. You discover that the allele frequency (how often
you see a particular allele) for all of the molecular markers on
Chromosome 1 is the same in obese patients as it is in the
general population. What does this result tell you about
potential mutations on Chromosome 1 contributing to obesity?
A. There are likely multiple mutations on Chromosome 1 contribute
to obesity
B. There is likely one mutation on Chromosome 1 contributes to
obesity
C. There are likely no mutations on Chromosome 1 contribute to
obesity
LOD Scores
Human linkage mapping
1
2
1
1
2
3
2
4
5
6
One person for this autosomal dominant trait in
generation III is recombinant - who?
A) 1
B) 2
C) 5
D) 6
I.
B1B3
1
B2B4
2
II.
B1B2
1
B3B4
2
B1B4
3
B1B4
4
B1B2
5
B3B2
6
Here is a pedigree showing another autosomal
dominant disease but with fewer generations. If
person II-1 is non-recombinant, who else in generation
II is non-recombinant?
A) II-3 and II-4 only
B) II-2, II-5, and II-6 only
C) II-2, II-3, II-4, and II-5 only
D) II-2, II-3, II-4, and II-6 only
A scientist studying VRS (Viagra resistance syndrome) has reported that he has
found a marker with a maximum LOD score of 22 at θ= 0.45 in a population on a
small island. Upon reading the article which statement below are you likely to say:
A) Big deal! Even with such a high LOD score, in terms of recombination
distance the VRS gene is located far away (greater than 40 map units) from the
marker so it is virutally unlinked.
B) That is kind of cool… That is a high LOD score and in terms of recombination
distance, the VRS gene is located at a medium distance (between 10-40 map
units) from the marker
C) Wow! That is such a high LOD score that the marker must be right next to
(within 10 map units) the VRS gene.
D) I am totally impressed! A LOD score of 22 means that there is 22:1 odds the
marker and gene are linked.