Genetics Ch 24
When phenotypic variance is determined solely by genotypic and environmental variance, and genetic and environmental factors are independent of one another, then total phenotypic variance is equal to genetic variance ___ environmental variance.
+
In a certain type of plant, the phenotypic variance for height is 10 cm2. VE = 6 cm2, VG = 4 cm2, and VA = 2 cm2. What is the narrow-sense heritability for this trait?
.2
In a population of chickens, the phenotypic variance for egg weight is 20 g2. VE = 8 g2, VG = 12 g2, and VA = 5 g2. What is the narrow-sense heritability of egg weight in this population of chickens?
.25
If the observed phenotypic correlation coefficient between related individuals is 0.20 and the expected correlation coefficient based on the known genetic relationship is 0.50, then the narrow-sense heritability for the trait is
.4
In a group of mice, the total phenotypic variance for body weight is 12.0 g2. The genetic variance is 9.0 g2, and the environmental variance is 3.0 g2. What is the broad-sense heritability for this trait?
.75
For a certain trait, the expected correlation coefficient for an aunt-niece relationship is 0.25. In a group of aunts and nieces, the observed correlation coefficient is found to be 0.20. What is the narrow-sense heritability for this trait?
.8
In an inbred strain of mice, the genetic variance for a quantitative trait is equal to
0, Monomorphic members of a population are all homozygous for the same allele of a given gene. Within such an inbred strain of mice, the VG equals zero.
When Nilsson-Ehle studied bread wheat, he found that hull color was determined by two genes. For the first gene, the R1 allele produces red color, and the r1 allele produces white color. Similarly, the R2 allele results in red pigment, and the r2 allele does not. The effects of the red alleles are additive. In a self-cross of a strain with genotype R1r1R2r1, what phenotypic ratio is expected in the offspring?
1:4:6:4:1
How many genes control seed weight in the graph shown?
3
In a certain type of plant, the stem is always at least 20 centimeters long. Two genes (A and B) with additive alleles influence the stem height. For these two genes, each dominant allele adds an additional 2 cm to the length of the stem; the recessive alleles do not change the length of the stem. If a plant with the genotype AaBb is allowed to self-cross, what proportion of the offspring will be 22 cm tall?
4/16
The heritability of fingerprint pattern is 0.97. This means that
97% of the phenotypic variance in fingerprint pattern is due to genetic variance.
What is a discontinuous trait?
A trait that falls into discrete categories
n bread wheat, hull color was initially believed to be determined by two genes (a third was later identified). The effects of the red alleles of these two genes are ___, meaning that a plant carrying more red alleles has a deeper red color.
Additive
The tendency of certain genotypes to be found preferentially in particular environments is called a genotype-environment ___.
Association
Which of the following are examples of quantitative traits?
Blood pressure in humans Speed of flight in birds Number of bristles in Drosophila
Characteristics that are determined by several genes and are also influenced by environmental factors are called ___ traits.
Complex
A quantitative trait that does not fall into discrete categories is referred to as a(n) ___ trait.
Continuous
A trait that can be assigned to a particular phenotypic category is called a(n) ___ trait.
Discontinuous
True or false: Quantitative traits are usually discontinuous.
False; Discontinuous traits can be put into discrete categories; in contrast, quantitative traits usually show a continuum of phenotypic variation.
True or false: Heritability can be used to define traits in a single individual.
False; Heritability is only applicable to populations of people.
A graph that presents phenotypic categories on the x-axis and the number of individuals that fall into a category on the y-axis is called a(n) ___ distribution.
Frequency
In the graph shown, under which condition will it be easier to assign phenotypic traits to genotypic categories?
Low environment effect; Since the curves are overlapping, it is difficult to assign unique genotypes to each phenotype.
What is inbreeding
Mating between close relatives
The table shown here presents data collected about fingerprint patterns. Based on the information in this table, which of the following conclusions is supported?
Most of the variability in fingerprint patterns can be explained by genetic variation among individuals.
What is the difference between natural selection and artificial selection?
Natural selection favors reproductive success, while artificial selection favors traits that are desirable to humans.
Transmission of a trait determined by two or more different genes is referred to as ___ inheritance.
Polygenic
Traits that are ______ often show a continuum of phenotypic variation.
Quantitative
Which of the following molecular markers have been used to construct genetic maps of the genomes of many species?
RFLPs, microsatelites, SNPs
A breeding strategy designed to modify phenotypes in an economically important plant or animal is called ___ breeding.
Selective
What type of analysis is used to analyze most polygenic quantitative traits?
Statistical
What is a quantitative trait locus?
The chromosomal location of one or more genes that affect the phenotype of a quantitative trait
A genotype-environment association is
The increased likelihood of finding certain genotypes in a particular environment.
For a quantitative trait, the narrow-sense heritability will be similar to the broad-sense heritability if
VA is large compared to VD and VI.
Genetic variance can be partitioned into three distinct categories. Match each type of variance with the correct description.
VA: variance due to the additive effects of alleles VD: variance due to the effects of alleles that follow a dominant/recessive pattern of inheritance VI:variance due to the effects of alleles with epistatic interactions
In a group of genetically homogeneous mice, the phenotypic variance for weight is 10 g2. In a group of genetically heterogeneous mice, the phenotypic variance for weight is 25 g2. Based on this information, what are the genetic, environmental, and phenotypic variances for the heterogeneous mice?
VG = 15 g2, VE = 10 g2, and VP = 25 g2
In a genetically homogeneous group of fruit flies, the phenotypic variance for abdominal bristles is 4 bristles2. In a genetically heterogeneous group of fruit flies, the phenotypic variance for abdominal bristles is 12 bristles2. What are the genetic, environmental, and phenotypic variances for this trait in heterogeneous flies?
VG = 8 bristles2, VE = 4 bristles2, and VP = 12 bristles2
Genetics plays a greater role than the environment in promoting phenotypic variation within a group when
VG is high and VE is low.
The phenotypic variance of a quantitative trait can be partitioned into several components. Match each component of variation to the correct description.
VGxE = Variation due to interactions between genetic and environmental factors VG<-->E = Variation due to associations between genetic and environmental factors
Which component of genetic variance is attributed to alleles that have additive effects?
Va
The data table shown here presents the longevity of two different strains of fruit flies at three different temperatures. The variation in longevity reported here is best described as
a genotype-environment interaction.
This figure depicts the varying effects of environmental factors on plants with three different genotypes. The variation represented here is best described as
a genotype-environment interaction.
In bread wheat, hull color was initially believed to be determined by two genes (a third was later identified). The effects of the red alleles of these two genes are ___, meaning that a plant carrying more red alleles has a deeper red color.
additive
Monomorphic members of a population
are homozygous for the same allele of a given gene.
Polygenic traits
are often difficult to organize into discrete phenotypic categories.
Selective breeding of plants and animals can result in
artificial selection
When a breeder chooses individuals with desirable traits to be parents, the result is ___ election. When environmental factors favor traits that enhance reproductive success, the result is ___ selection.
artificial; natural
For a quantitative trait, the outcome of a cross can be predicted most reliably based on the effects of alleles that
behave additively.
If heritability is high
changing the environment may still have an impact on the outcome of the trait.
When the genetic variance for a trait is low and the environmental variance is high, most of the phenotypic variation within a group can be attributed to
environmental factors
In inbred strains of mice, all phenotypic variance is due to
environmental variance.
When a quantitative trait is analyzed, its phenotypic variation can be partitioned into ___ variation, ___ variation, and the interactions and associations between them.
genetic; environmental
When narrow-sense heritability is calculated from correlation coefficients, an assumption that is inherent in the computation is that
genetics and the environment are independent variables.
Genetic studies that compare quantitative traits in identical versus fraternal twins can be used to evaluate how a quantitative trait is affected by
genotype-environment associations.
Heritability tells us the relative contributions of genetic variation and environment in influencing phenotypic variation in a particular ___ in a particular ___.
group; environment
For a particular population in a particular environment, the amount of phenotypic variation that is due to genetic variation is called
heritability
A heritability value of 0.6 for IQ testing ability means that
in the examined population, 60% of the variation in IQ ability is due to genetics and 40% of the variation is due to the environment.
The chromosomal location of one or more genes that influence a quantitative trait is called a quantitative trait ___.
locus
RFLPs, SNPs, and microsatellites are variable sequences and are examples of molecular ___ that have been used to map the genomes of many species.
markers
The goal of selective breeding is to
modify phenotypes in economically important plants and animals.
A population in which all members of the population are homozygous for the same allele of a given gene is referred to as
monomorphic
A frequency distribution in which a trait varies in a symmetrical way around an average value is called a(n) ___ distribution. The distribution of many biological characteristics produces a(n) ___-shaped curve.
normal; bell
A frequency distribution is a graph that shows the
number of individuals in various phenotypic categories.
Which methods can be used to determine narrow-sense heritability?
outcomes of selective breeding practices measurements of a quantitative trait among groups of genetically-related individuals
If VA is very large in comparison to VD and VI, then narrow-sense heritability will be
pproximately the same as broad-sense heritability.
The field of genetics that studies the inheritance of complex traits is called ___ genetics.
quantitative
The length of an ear of corn is an example of a(n)
quantitative trait.
Narrow-sense heritability can be determined through ___ breeding practices with agricultural species or by measuring a ___ trait among groups of genetically-related individuals.
selective; quantitative
In studies of human genetics, the effects of genotype-environment associations can be minimized by studying
siblings adopted at birth by different parents.
When genetic and environmental factors are independent of one another, and genetic variance (VG) and environmental variance (VE) are the only factors that determine total variance (VT), then VT is equal to the
sum of VG and VE.
In analyzing quantitative traits, geneticists focus on VA and ignore VD and VI because
the additive effects of alleles allow the prediction of the outcomes of crosses.
A genotype-environmental interaction exists when
the environmental effects on phenotype differ according to genotype.
Which characteristic of human fingerprints has been shown to have high heritability?
the number of ridges between triple junctions on all fingers
In bread wheat, the color of the hull can be dark red, white, or various intermediate shades of red. Initial genetic analysis of this trait by Herman Nilsson-Ehle demonstrated that hull color is controlled by
two loci with additive effects on hull color.
Polygenic inheritance is the transmission of a trait that is determined by
two or more different genes
Genotype-environmental interaction (represented by VG x E) is
variation attributed to interactions between genetic and environmental factors.
