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Genetics > CHAPTER 19 > Flashcards

CHAPTER 19 Flashcards

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Biology 101 flashcards
1
Q

Single Gene traits

A
  • Discontinuous
  • Discrete, sharply distinguishable categories
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2
Q

Polygenic and multifactorial traits

A

Show continuous variation

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3
Q

Genetic potential of Human height

A
  • A multifactorial trait with continuous variation
  • Effected by developmental and environmental factors - nutrition, exercise, rest
  • Parents transmit a genetic potential to offspring that may or may not be met, depending on various influence
  • Adult height >700 genetic variants
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4
Q

Polygenes and differential gene effects

A
  • Null model: each gene contributes the same
  • Different genes contribute differently: major and modifier genes (less influence)
  • Additive genes: each gene contributes an incremental amount to phenotypic value - alleles of each additive gene can be assigned a value of contribution
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5
Q

Multiple-Gene Hypothesis

A

Alleles of each of the contributing genes obeyed the principles of segregation and independent assortment and had an additive effect in the production of phenotypic variation
- Two genes, two alleles each
- Alleles A1 and B1 each add one unit to phenotype
- Alleles A2 and B2 add nothing

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6
Q

Number of phenotypes from additive genes

A

= 2n+1, where n is the number of genes
- more genes, more phenotypes, less demarcation between categories

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7
Q

Frequency of most extreme phenotypes based on number of genes contribution to trait

A

4 ^ number of genes

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8
Q

Allele segregation in quantitative trait production

A

Variation in pure-breed strands indicates;
1. Allelic segregation at multiple genes
2. Environmental effects

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9
Q

Effect of the environment on phenotypes

A
  1. No gene-environment interaction
    - A discrete phenotype for each genotype
  2. Moderate gene-environment interaction
    - Minor overlaps between phenotypes in the F2
  3. Substantial gene-environment interaction
    - Wide phenotypic ranges and significant overlaps
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10
Q

GEI

A

Genotype-environmental interactions
- Estimated only when several genotypes are assayed in several defined environments

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11
Q

Determining phenotype when affected by specific environmental factors

A

Phenotype = Genotype + Environment + Genotype-environment interactions

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12
Q

Threshold Trait

A

dichotomous phenotypic trait controlled by multiple genes
- Continuous distribution of genetic liability in general population
- Threshold of genetic liability determines affected vs unaffected

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13
Q

Threshold of genetic liability

A

The point beyond which an individual will show the affect phenotype
- Environmental factors can contribute to reaching threshold

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14
Q

Goals of Quantitative Genetics

A
  1. How much is the phenotypic variation contributed by genetic factors
  2. How many genes influence the specific phenotypic trait
  3. How much does each of the genes contribute to the phenotypic variation
  4. How do genes interact with each other to influence phenotypic variation
  5. How do genes interact with environmental factors to influence phenotypic variation
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15
Q

Descriptive statistics of quantitative trait analysis

A
  • Mean
  • Mode
  • Median
  • SD
  • Variance
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16
Q

Variance

A

s^2 is a measure of the spread of distribution around the mean
= sum of (xi - x)^2/df

17
Q

Standard deviation

A

s = sqrt s^2

18
Q

Phenotypic variance

A

Vp= Vg + Ve
- Genetic variance is the genotypic contribution
- Environmental variance is the environmental contribution

19
Q

What are the 3 allelic effects on genetic variance

A
  1. Additive variance: added effects of all alleles contributing to the trait
  2. Dominance variance: contributions due to heterozygous individuals not having intermediate phenotype between the two homozygous states
  3. Interactive variance: epistatic interactions between alleles of different genes
20
Q

Types of quantitative variation in a population

A
  • Phenotypic variation
  • Genetic variation
  • Environmental variation
  • Genotype-environment interaction variations
21
Q

Heritability

A

The proportion of phenotypic variation that is due to genetic variation

22
Q

What are the two measures of heritability

A
  • Broad-sense heritability (H^2): H^2 = VG/VP
  • Narrow-sense heritability (h^2): h^2 = Va/Vp
23
Q

Analyzing phenotypes of monozygotic twins

A

Share all their alleles
Vp=VE

24
Q

Analyzing phenotypes of dizygotic twins

A

About 50% their alleles are shared
VP=Ve +Vg

25
Q

Narrow sense heritability

A

The proportion of phenotypic variation due to additive genetic variation (h^2 = Va/Vp)
- High NSH correlates with a greater degree of response to selection

26
Q

What are four attributes of heritability that are central to its meaning

A
  1. It is a measure of the degree to which genetic differences contribute to phenotypic variation of a trait
  2. Heritability values are accurate only for the environment and population in which they are measured
  3. Heritability for a given trait in a population can change
  4. High heritability does not preclude environmental factors
27
Q

Common sources of error in twin studies

A
  1. Stronger shared maternal effects in identical twins than in fraternal twins
  2. Greater similarity of treatment of identical twins than of fraternal twins
  3. Greater similarity of interactions between genes and environmental factors twins than in fraternal twins
28
Q

Selection differential

A

The difference between the population mean value and the mean trait value for the mating population

29
Q

Response to selection

A

The extent to which difference between the mating trait value and the population mean value can be passed on to progeny

30
Q

Heritability and responses to natural selection

A

Higher heritability, closer in value R and S making mean of offspring resemble mean of mating population

31
Q

Quantitative Trait loci

A

Genes that contribute to phenotypic variation in quantitative traits

32
Q

GTL mapping

A

Mapping QTLs to chromosome regions/ linkage groups

33
Q

GTL mapping strategies

A
  1. Analyzing genetic crosses
  2. Genome-wide association studies
34
Q

Analyzing Genetic Crosses

A
  • Construct genetics crosses between parental strains with different phenotypes
  • Develop DNA markers that differ between parental strains
  • Obtain phenotype and genotype of all progeny
  • Identify associations between phenotype and genotype at individual loci
35
Q

Genome-wide association studies for QTL Mapping Strategy

A

GWAS try to identify whether a particular sequence variant is associated with a specific phenotype in a natural population
1. Select a natural population and obtain their phenotype data
2. Obtain their whole-genome sequences
3. Compare “case” and “controls” to assess their genotypic difference at each sequence variant
4. Nucleotide frequencies showing significant differences between “cases” and “controls” are candidate QTL
5. Need to correct for “false discovery rate” to reduce false positives

Genetics (18 decks)

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