Which statement is true for quantitative traits?
a. Quantitative traits are those for which phenotypes vary
continuously.
b. Quantitative traits are influenced by multiple genes and
environmental factors.
c. Quantitative traits are those that can be measured on a
continuous scale.
d. Quantitative traits are those for which multiple genes contribute
in an equal and additive way to the phenotype.
e. All of the above are always true.
answer
E
question
Suppose that pumpkin weight is controlled by five unlinked loci, each with two segregating alleles (A/a, B/b, C/c, D/d, E/e) that have additive effects. What fraction of the F2 offspring from a cross of AABBCCDDEE and aabbccddee parents are expected to have the same weight phenotype as the aabbccddee parent?
a. ¼
b. 1/10
c. (1/2)5
d. (1/4)5
answer
D
question
Assuming normal distribution, the mean +/- 2 standard deviations should include approximately how much of the total measurements?
a. 50%
b. 66%
c. 95%
d. 99%
answer
C
question
How can heritability be measured?
a. Compare individuals with different degrees of
relatedness.
b. Eliminate one of the variance components.
c. Analyze regression observed from parents to
offspring.
d. All of the above methods can be used to measure
heritability.
answer
D
question
To measure heritability it is easiest if:
a. you determine the regression between parents and offspring.
b. you control environmental components.
c. you use genetically identical individuals.
d. you measure a response to selection.
answer
C
question
Heritability:
a. is universal for a given trait.
b. is the degree to which a specific characteristic is
genetically determined.
c. is specific for a given population in a specific
environment.
d. can be used as a quantitative measure of genetic differences between two populations.
answer
C
question
Genetic-environmental interaction variance is:
a. the total variance of a trait in a population.
b. the sum of the genetic variance and the environmental variance.
c. the effect of a gene depending on the environments.
d. the phenotypic variance.
e. None of the above.
answer
C
question
Genetic variance includes:
a. additive genetic variance.
b. dominance genetic variance.
c. genic interaction variance.
d. A and B.
e. A,B and C.
answer
E
question
The _____________ is the statistic that measures the spread of a distribution around the mean.
a. correlation coefficient
b. regression coefficient
c. variance
d. average
answer
C
question
If broad-sense heritability for a trait is very high and narrow-sense heritability is very low, which of the following must be TRUE?
a. Additive variance must be high relative to total phenotypic
variance.
b. Dominance variance must be high relative to total phenotypic variance.
c. Environmental variance must be high relative to total phenotypic variance.
d. Genotypic-environmental covariance must be high relative to total phenotypic variance.
e. No conclusions can be drawn without additional information.
answer
B
question
A Mendelian population is one that:
a. is a group of interbreeding members of a species.
b. evolves through changes in its gene pool.
c. meets Hardy-Weinberg equilibrium conditions.
d. A and B.
e. All of the above.
answer
D
question
Blue eyes are recessive to brown eyes in humans. If the frequency of blue-eyed individuals in a population is 16%, we can calculate that the frequency of the allele for blue eyes is:
a. 16%.
b. 32%
c. 40%
d. 48%
e. None of the above.
answer
C
question
The Hardy-Weinberg equilibrium requires all of the following assumptions EXCEPT:
a. mating is random.
b. the population is small.
c. no selection is taking place.
d. there is no immigration or emigration.
e. Actually, it requires all of these assumptions.
answer
B
question
All of the following describe effects of natural selection EXCEPT:
a. it promotes adaptation.
b. it reflects differential survival and reproduction according to phenotype.
c. it always produces an equilibrium.
d. it can lead to unstable equilibria.
answer
C
question
In four o'clock plants, two alleles (R, r) produce three petal colors. RR plants have red petals, rr plants have white petals, and heterozygotes have pink petals. In a particular population of four o'clocks there are 40 plants with red petals, 50 plants with pink petals, and 10 plants with white petals. What is the frequency of the r allele in this population?
a. 0.10
b. 0.20
c. 0.35
d. 0.60
e. 0.70
answer
C
question
When they are at equilibrium, allelic frequencies are determined by _________.
a. reverse mutation rates
b. forward mutation rates
c. Both a and b.
d. Neither a nor b.
answer
C
question
Migration can:
a. decrease genetic differences between two populations.
b. increase genetic differences between two populations.
c. increase the variation within a population that receives migrants.
d. Both a and c.
e. Both b and c.
answer
D
question
Sickle-cell anemia is a recessive disease that afflicts approximately 1 in 12 African Americans, meaning that the frequency of ss homozygotes is 0.09. Assuming the African American population is in H-W equilibrium, what is the frequency of Ss carriers in this population?
a. pq = (0.7)(0.3) = 0.21
b. 2pq = 2(0.7)(0.3) = 0.42
c. 1 - q2 = 1 - 0.09 = 0.91
d. 1 - q = 0.7
e. Cannot determine without more information.
answer
B
question
Population genetics
answer
studies the genetic makeup of the population and how the genetic composition changes over time
question
Population
answer
group of individuals of the same species in a defined location
question
Gene pool
answer
the complete set of genetic information within a population
question
What can population genetics describe?
answer
the genetic structure of a population by determining the frequencies of genotypes and alleles in a population
question
Genotype frequency
answer
given N individuals, you have X AA, Y Aa, and Z aa, then find each frequency of genotypes
- i.e. AA freq = X/N
question
Allelic frequency
answer
the allelic frequency indicates a proportion of a certain allele at a particular locus in a population
question
Formula for allelic frequency of p?
answer
p = (2*NAA + NAa)/2N
question
Formula for allelic frequency of q?
answer
q = (2*Naa + NAa)/2N
question
Formula for allelic frequency of p if it is an X-linked loci?
answer
p = f(XA) = f(XAXA) + 1/2f(XAXa) + f(XAY)
question
Hardy-Weinberg Law
answer
mathematical model used to evaluate the effect of reproduction on the genotypic and allelic frequencies of a population
question
Assumptions of Hardy-Weinberg Law
answer
1. No selection occurs
2. No mutations
3. No migration
4. No sampling errors (all alleles adequately represented)
5. Mating is random
question
Properties of Hardy-Weinberg Law
answer
1. Allele frequencies predict genotype frequencies
2. At EQ, allele and genotypic frequencies do not change from generation to generation
3. EQ is reached in one generation of random mating
question
Genetic equilibrium
answer
allele frequency in a population remains constant from generation to generation
question
When do you apply Hardy-Weinberg?
answer
Loci with two alleles, multiple alleles, or X-linked loci
selection of one trait over another due to reproductive success
- adaptive traits that produce more offspring will occur more
- adaptive traits appear with higher allele frequencies
question
Mutation
answer
source of novel alleles in a population
- combined with other effects, they have a greater effect on the population
question
Migration effects
answer
1. Causes gene pools to become more similar
2. Adds genetic variation to populations so different alleles may arise
question
Genetic drift
answer
variation in the relative frequency of different genotypes in a small population, owing to the chance disappearance of particular genes as individuals die or do not reproduce
- as population sizes decrease, allele fluctuations can increase
- i.e. epidemics, population isolation
question
Consequences of inbreeding
answer
1. frequency of heterozygous offspring is lower than with random mating
2. decrease in heterozygous individuals in a population
3. homozygosity increases because identical alleles are brought together at a locus (permits expression of recessive alleles that may have been masked by a dominant allele in the parents
4. selfing - most severe form that reduces heterozygosity by 50%
question
What allelic frequencies must occur for inbreeding?
answer
p = q = 0.5
question
Why is inbreeding deleterious for most species?
answer
- increase in poor immune response
- increased expression of recessive deleterious genes that reduce survival, fertility, and physiological vigor
question
What occurs within populations when genetic variation increases?
answer
Mutation
Migration
Natural selection
question
What occurs within populations when genetic variation decreases?
answer
Genetic drift
Natural selection
question
What occurs between populations when genetic variation increases?
answer
Mutation
Genetic drift
Natural selection
question
What occurs between populations when genetic variation decreases?
answer
Migration
Natural selection
question
Sexual reproduction
answer
combination of haploid gametes (sperm and egg) from two sexes to form a diploid embryo (zygote)
question
How is sex determined? (3 ways)
answer
1. Chromosomal sex determination
2. Genic sex determination
3. Environmental sex determination
question
How many pairs of chromosomes do humans have?
answer
23
question
What is the size of the Y chromosome?
answer
1/3 the size of X
question
How many genes does the Y chromosome have?
answer
1/100th
question
Pseudoautosomal regions
answer
Ends of X and Y chromosomes where X-Y pair in meiosis in the male
question
What is the shape of the Y chromosome?
answer
acrocentric
question
What percentage of Y is the non-recombining region (NRY) or male-specific region (MSY) of Y?
answer
95%
question
SRY gene
answer
Sex-determining region of Y that determines the male and encodes a protein called testis-determining factor (TDF)
question
What occurs with the absence of the Y chromosome?
answer
female phenotype - Turner's syndrome
question
How many copies will occur if a locus controlling a trait is located on the X chromosome in females?
answer
2
question
How many copies will occur if a locus controlling a trait is located on the X chromosome in males?
answer
1
question
Morgan's experiment
answer
Crossed a red-eyed female (X+X+) and white-eyed male (XwY)
- found eye color is located on X chromsome
question
Why do males have a higher chance of exhibiting recessive phenotypes?
answer
Males only need to inherit one recessive allele to show an X-linked trait (only from mother) vs. females who need to inherit two recessive alleles to show an X-linked trait (one from mother and father)
question
Dosage compensation
answer
inactivation of one X-chromosome in the female during interphase
question
Barr body
answer
inactivated X-chromosome areas (genes) on one of the X-chromosomes visible in the nucleus of the cells in placental mammals
question
Lyon Hypothesis
answer
X-inactivation is random and happens early in development (within the first few weeks)
- in heterozygous females, 50% of cells express one allele and 50% express another; once X is inactivated, it remains inactivated in all somatic cells that descend from the cell
- produces a patchy or mosaic pattern for the expression of an X-linked character in heterozygous females
question
Lyonization
answer
X-inactivation yielding a Barr body
question
Xist gene
answer
X-inactivation-specific-transcription gene
- produces an RNA molecule that coats the X chromosome and inactivates the genes on it by altering the chromatin structure
question
What happens to the Xist gene on an active X chromosome?
answer
The gene is repressed
question
Nilsson-Ehle's cross
answer
Crossed a variety of wheat that possessed purple kernels and created F1 generation of red kernels --> F2 generation of different colors
question
How to determine the number of F2 that resemble the original homozygous parent?
answer
(1/4)^n where n = number of loci
question
Phenotypic variance (VP)
answer
Result of genetic variance (VG), environmental variance (VE), and interaction between both (VGxE)
VP = VG + VE + VGxE
question
Genetic variance (VG)
answer
Result of additive genetic variance (VA), dominant genetic variance (VD), and epistasis [interaction between loci] (VI)
VG = VA + VD + VI
question
Heritability
answer
proportion of total phenotypic variation that is due to genetic differences
question
Broad-sense heritability (H2)
answer
represents the proportion of phenotypic variance that is due to genetic variance
H2 = VG/VP
question
Narrow-sense heritability (h2)
answer
represents the proportion of phenotypic variance is due to additive genetic variance
h2 = VA/VP
question
How does the intercept of a line (b) explain genetic variation?
answer
â–¡ If b = h2=0, no additive genetic basis for the phenotype
â–¡ If b = h2 = 1, 50% of the phenotypic variance is due to additive genetic variance
â–¡ If b = h2 = 0.5, offspring and parents have nearly same phenotype, no effect of environment
question
Limitations of heritability
answer
1. Doesn't provide info about an individual's genes or the environmental factors that control the development of a characteristic
2. Reflects genetic variation accounting for a trait's phenotypic variance, not whether genes per se play a role in the trait expression
3. Even when heritability is high, environmental factors may influence a characteristic
4. Says nothing about the nature of differences between groups
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