Genetic and Phenotypic Variation I Flashcards
What is the ultimate source for all novel genetic variation?
Mutation
Define mutation.
A novel genetic difference between a parent and its offspring
What is a point mutation?
Base pair substitutions in DNA sequences
Describe the mechanism of point mutations.
Chance errors during DNA synthesis or during repair of damaged DNA.
What is the significance of point mutations?
Create new alleles
What is a chromosome inversion?
Flipping of a chromosome segment so order of genes along the chromosome
What is the mechanism of chromosome inversions?
Breaks in DNA caused by radiation or other insults
What is the significance of chromosome inversions?
Alleles inside the inversion are likely to be transmitted together, as a unit
What is gene duplication?
Duplication of a short stretch of DNA, creating an extra copy of the sequence.
What is the mechanism of gene duplication?
Unequal crossing over during meiosis or retrotransposition.
What is the significance of gene duplication?
Redundant new genes may acquire new functions by mutation.
What is genome duplication?
Addition of a complete set of chromosomes.
What is the mechanism of genome duplication?
Errors in meiosis or, in plants, mitosis.
What is the significance of genome duplication?
May create new species
Define homozygous
Identical alleles at the same locus on homologous chromosomes
Define heterozygous.
Different alleles at the same locus on homologous chromosomes
Describe dominance.
One allele masks the expression of the other allele
Define partial dominance.
One allele partially masks the expression of another allele
Describe recessive
Expression of allele only evident when homozygousD
Describe additive
Equal contributions to expression
Define allele frequency.
Fractional representation among all the alleles present in the population
How is allele frequency calculated?
f = number of allele present in the population/total alleles in the population
Describe the conditions required for the HWE Principle.
IF…
1. There is no selection
2. There is no mutation
3. There is no dispersal
4. There are no chance events (i.e., infinite population size)
5. Individuals rate at random
We can predict the stable frequency of a gene using the Hardy-Weinberg Equilibrium Principle.
What is the HWE Principle?
- Allele frequencies at a locus come into equilibrium within one generation, and they will not change from generation to generation, as long as the five assumptions are met
- Genetic variation can be maintained within a population without any evolutionary mechanism
- If the allele frequencies in a population are given by p and q, then:
p2 = frequency of homozygotes at allele #1
2pq = frequency of heterozygotes
q2 = frequency of homozygotes at allele #2
p2 + 2pq + q2 = 1
How is genetic variation quantified for Mendelian segregated traits controlled at a single locus?
- Observed or predicted (HW) heterozygosity within a population
- Number of alleles at a locus
How is genetic variation quantified for Mendelian segregated traits controlled at two or more loci?
- Average heterozygosity
- Average number of alleles per locus
How is heritability estimated?
- Plot midoffspring trait values vs. midparent trait values; slope of best fit line gives estimate of heritability
What does a slope of 0 for a plot of midoffspring trait values vs. midparent trait values indicate? A slope of 1?
o Slope of 0 – no resemblance
o Slope of 1 – perfect resemblance
What are the 4 confounding issues that can complicate heritability estimates based off of graphs/
Misidentified paternity
Conspecific nest parasitism
Shared environments
Maternal effects
What is misidentified paternity and how can it be avoided?
o Social father is not biological father
o Can be avoided using genetic paternity tests
What is conspecific nest parasitism? How can this be avoided?
o Social mother may not be biological mother
o Some females sneak into other nests and lay extra eggs
o Genetic tests can avoid this
How can shared environments complicate heritability estimateS?
o Relatives share their environment as well as their genes
o Correlation due to shared environment inflates heritability measurements
What is a possible solution to the complications in heritability estimates due to shared environments?
Cross-fostering/common garden/reciprocal-transplant experiments
What are maternal effects? How can these be avoided?
o Differences in the nutrient stores or hormonal contents of eggs
o Avoid by estimating heritabilities from fathers only
Outline the three steps in measuring diversity at a particular gene.
- Determine the genotypes of a large sample
a. Typically look at DNA - Determine the frequency of the relevant allele(s)
a. Frequencies of all alleles should sum to 1
b. Can do based on genotype or allele frequency - Summarize data (two possible statistics)
What are the two possible statistics in measuring diversity of alleles at a particular gene?
Mean heterozyogisty
Percentage of polymorphic loci
What is mean heterozygosity?
i. Average frequency of heterozygotes across loci/fraction of genes that are heterozygous in the genotype of the average individual
What is percentage of polymorphic loci?
i. Fraction of genes in a population that have at least 2 alleles
How do you calculate the probability that two independent events will occur together?
Product of individual probabilities
How do you calculate the probability that one or the other of two mutually exclusive events will occur?
Sum of individual probabilities
What is the HWE Principle with more than two alleles?
If there are three alleles with frequencies p1, p2, and p3 such that
p1 + p2 + p3 = 1
then the genotype frequencies are given by
(p1 + p2 + p3) = p12 + p22 + p32 + 2p1p2 + 2p1p3 + 2p2p3
And the allele frequencies do not change from generation to generation.
What are the five steps of the statsitiscal analysis of allele and genotype frequencies using the chi square test?
Calculate the allele frequencies
Calculate the genotype frequencies expected under HW equilibrium
Calculate the expected number of infants of each genotype under HW equilibrium
Expected number of each genotype multiplied by total number of infants
Calculate a test statistic:
χ^2=∑▒(observed-expected)^2/expected
Determine whether the test statistic is significant
How do you determine whether the test statistic is significant?
a. Calculate degrees of freedom
i. # of classes - # of independent values calculated from the data
b. Use table to find critical value
