Chap 20 Flashcards
Height in humans, milk and meat production in cattle, field in various crops are controlled by many ___
Genes
This ___ is measured and described in quantitative terms and is known as ____
Continuous variation; quantitative inheritance
A continuous quantitative trait is often the results of ___ and is frequently influenced by the ___ or ___
Polygenic inheritance; environment; multifactorial
___ is determined by a single gene
Simple trait
___ trait determined by two or more genes
Polygenic trait
___ trait determined by 2 or more genes +/-environmental contribution
Multifactorial trait
___ phenotypes fall into distinct categories (red vs. white)
Discontinuous variation
___ phenotypes varies over range, with most falling ~ midway between the extremes
Continuous variation
Bateson and Yule proposed the ___ or the ___ in which many genes, each individually behaving in a Mendelian fashion, contribute to the phenotype in a cumulative or quantitative way
Multiple-factor; multiple-gene hypothesis
This ___ hypothesis is demonstrated by grain color in wheat to test the concept that the cumulative effects of alleles at multiple loci produce the range of ___ seen in ___ traits.
Multiple-gene; phenotypes; quantitative
Each gene has an ___ allele and a ____ allele
Additive; nonadditive
The greater the number of ___ alleles in the ___, the more intense the red color expressed in the phenotype
Additive; genotype
Each ___ allele contributes equally to pigment in the grain, and the _____ allele failed to contribute to any pigment
Additive; nonadditive
What are the multiple-gene hypothesis consists of the following major points?
- Phenotypic traits show continuous variation that can be quantified by measuring, weighing, etc.
- Two or more loci show an additive effect on expression of the phenotype and is called polygenic inheritance
- An additive allele contributes an equal amount to the phenotype, whereas a nonadditive contributes nothing
- Each additive alleles contribute to a single quantitative trait to produce substantial phenotypic variation
- The additive alleles contribute to a single quantitative trait to produce substantial phenotypic variation
The number of __ contributing to a ___ trait can be estimated based on the ratio of F2 individuals resembling either of the two extreme P1 phenotypes
Polygenes; quantitative
For low numbers of ___, the number of ___ loci n can be estimated from the total number of possible ___
Polygenes; additive; phenotypes
The estimates of low numbers of Polygenes estimates assume that all of the __ alleles contribute equally and ___. There are no significant environmental effects on ___ expression.
Additive; additively; phenotypic
__ traits are usually measured in a sample of individuals that is __ and __ of the population from which it is drawn
Polygenic; large; representative
The data often form a ___ distribution that is a characteristic bell-shaped curve when plotted as a frequency histogram
Normal
Measurements clustering around a central point called a ____ and the central point is the mean
Central tendency
___ is the average of a set of measurements
Mean
___ provides information about the spread of data around the mean
Variance
If multiple individuals have same measurement, data for each measurement class can be ___
Grouped
___ deviation is the square root of the variance
Standard
Two phenotypic traits may ___ variation in one trait may be ___ on/associated with variation in a second trait
Correlate; dependent
___ is a measurement of how much variation is common to both quantitative traits
Covariance
The ___ coefficient indicates to what extent variation in one trait is associated with variation in a second trait
Correlation
When r is ___, the two traits both increase or decrease together or one increases as the other decreases when r is ___
Positive; negative
___ indicate that an increase in the measure of one traits tends to correlate with an increase in the measure of the second trait
Positive values
___ indicate that an increase in one trait tends to be associated with a decrease in the measure of the second trait
Negative values
___ described the proportion of total phenotypic variation in a population due to genetic factors
Heritability
For a ___ trait, high heritability means most variation is due to ___ factors and less ____ impact
Multifactorial; genetic; environmental
With low heritability, environmental factors are likely to have a ___ impact on ___
Greater; phenotype
A heritability estimate tells the proportion of ___ variation that can be attributed to ___ variation within a certain population in a particular environment
Phenotypic; genetic
Total ___ variance can be divided into ___ variance or ___ variance
Phenotypic; genotypes; environmental
When obtaining ___ estimates for multi-factorial traits, researchers often assume that the genotype by environment interaction is small enough to ignore or combine with ___ variance
Heritability; environmental
In order to minimize genetic differences between individuals, researchers of tern compare highly inbred ___ and ___ species when estimating heritabilities
Plant; animal
Expose different members of the same inbred strain to ___ environments to estimate VE
Different
Expose different inbred strains to the ___ environment to estimate VG
Same
Broad sense heritability (H2) measure the contribution of the ___ variance to the total ___ variance
Genotypic; phenotypic
A value approaching 1.0 indicates that the environment has ___ impact on the ___ variance
Little; phenotypic
Low values close to 0.0 indicate that ___ factors, and not the ___ are responsible for ___ variation within a population
Environmental; genotype; phenotypic
Estimates of ___ heritability are expressed as percentage values for traits among different ____
Narrow-sense; organisms
Narrow-sense heritability more valuable predictor of response to ___
Selection
Narrow-sense heritability is the proportion of phenotypic variance due to additive ___ alone
Genotypic variance
Narrow-sense heritability estimate are valuable to plant and animal breeders because they estimate the proportion of total ____ variance for that trait that is due to ____ variance
Phenotype; additive genetic
It is best to select individuals with superior ___ for the desired ___ trait from a ___ population and to breed offspring from those individuals
Phenotypes; quantitative; heterogeneous
Artificial selection:
- Choosing specific individuals with ___ from initially ___ population for future breeding
- Purpose is to develop population containing high frequency of individuals with \_\_\_ traits
Preferred phenotypes; heterogenous; desired
Artificial trait selection:
- Can be __ and multifactorial
- Traits of ___ importance:
- crops and livestock
- grain yield in plants
- weight gain or milk yield in cattle
- speed or stamina in horses
Polygenic; economic
Realized heritability:
- ___ breeding estimate potential success for artificial selection
Selective
Heritability values:
- Provide no information on genes involved in ___
- Measure in populations- limited application to ___
Traits; individuals
Future changes in ___ factors can affect ___
Environmental; heritability
Humans twins are useful for examining ___ versus ___ variance for a multifactorial trait
Genotypic; environmental
For monozygotic (MZ) or identical twins, ___ variance is due to VE environmental variance, as there is no VG Genotypic variance
Phenotypic
For dizygotic (DZ) or fraternal twins, ___ difference represent both environmental variance and approximately half the Genotypic variance
Phenotypic
Comparison of phenotypic variances for the same trait in identical and fraternal twin sets provides an estimate of ____ heritability of the Genotypic variance to the total ___ for that trait
Broad-sense; phenotypic
The difference in ___ for a given trait in identical versus fraternal twins suggests whether a strong genetic component is involved in ___ of the trait
Concordance; determination
Twins are ___ for a trait if both or neither ___ it
Concordant; express
If one expresses it and the other does not, the pair is said to be ___ for that trait
Discordant
MZ twins are treat more ___ than DZ twins, which may ___ environmental variance among DZ twins
Equally; inflate
Interactions between ___ and ___ may produce variability in phenotype, which can ___ total phenotypic variance of DZ twins compared to MZ twins raised in the ___ environment
Genotype; environment; increase; same
The assumption that MZ twins share the same ___ has been valuable for estimating heritability for many ___ diseases such as cardiovascular disease, diabetes, mental illness
Genome; multifactorial
Results from ___ research has challenged whether MZ twins are truly ___
Genomic; identical
Most recent genomic discoveries about identical twins include the following:
By the time MZ twins are born, they do no necessarily have identical ___
- they develop from a single egg but become two independent ___
- genotypes can diverge slightly with differences in copy number variation (CNV)- variation in number of copes of numerous large DNA sequences resulting in ___ mosaicism
-CNV difference between MZ twins has been associated with ___ lymphoma in one twin but not the other
Genomes; embryos; somatic; chronic
Gene-expression patterns in MZ twins change with age, leading to ___ differences
- This involves ___- the chemical modification of their DNA and associated histone
- MZ. Twins are epigenetically ___ at birth, but adult MZ twins show significant ___ in methylation patterns of both DNA and his tones, which in turn affect gene expression
-Progressive age-related genomic ___ may be due to expire to ___ environments or to failure of epigenetic marking following DNA replication
Phenotypic; epigenetics; identical; differences; modifications; different
