Genetic and Phenotypic Variation I

Question 1

What is the ultimate source for all novel genetic variation?

Answer 1

Mutation

Question 2

Define mutation.

Answer 2

A novel genetic difference between a parent and its offspring

Question 3

What is a point mutation?

Answer 3

Base pair substitutions in DNA sequences

Question 4

Describe the mechanism of point mutations.

Answer 4

Chance errors during DNA synthesis or during repair of damaged DNA.

Question 5

What is the significance of point mutations?

Answer 5

Create new alleles

Question 6

What is a chromosome inversion?

Answer 6

Flipping of a chromosome segment so order of genes along the chromosome

Question 7

What is the mechanism of chromosome inversions?

Answer 7

Breaks in DNA caused by radiation or other insults

Question 8

What is the significance of chromosome inversions?

Answer 8

Alleles inside the inversion are likely to be transmitted together, as a unit

Question 9

What is gene duplication?

Answer 9

Duplication of a short stretch of DNA, creating an extra copy of the sequence.

Question 10

What is the mechanism of gene duplication?

Answer 10

Unequal crossing over during meiosis or retrotransposition.

Question 11

What is the significance of gene duplication?

Answer 11

Redundant new genes may acquire new functions by mutation.

Question 12

What is genome duplication?

Answer 12

Addition of a complete set of chromosomes.

Question 13

What is the mechanism of genome duplication?

Answer 13

Errors in meiosis or, in plants, mitosis.

Question 14

What is the significance of genome duplication?

Answer 14

May create new species

Question 15

Define homozygous

Answer 15

Identical alleles at the same locus on homologous chromosomes

Question 16

Define heterozygous.

Answer 16

Different alleles at the same locus on homologous chromosomes

Question 17

Describe dominance.

Answer 17

One allele masks the expression of the other allele

Question 18

Define partial dominance.

Answer 18

One allele partially masks the expression of another allele

Question 19

Describe recessive

Answer 19

Expression of allele only evident when homozygousD

Question 20

Describe additive

Answer 20

Equal contributions to expression

Question 21

Define allele frequency.

Answer 21

Fractional representation among all the alleles present in the population

Question 22

How is allele frequency calculated?

Answer 22

f = number of allele present in the population/total alleles in the population

Question 23

Describe the conditions required for the HWE Principle.

Answer 23

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.

Question 24

What is the HWE Principle?

Answer 24

1. 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
2. Genetic variation can be maintained within a population without any evolutionary mechanism
3. 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

Question 25

How is genetic variation quantified for Mendelian segregated traits controlled at a single locus?

Answer 25

* Observed or predicted (HW) heterozygosity within a population * Number of alleles at a locus

Question 26

How is genetic variation quantified for Mendelian segregated traits controlled at two or more loci?

Answer 26

* Average heterozygosity * Average number of alleles per locus

Question 27

How is heritability estimated?

Answer 27

* Plot midoffspring trait values vs. midparent trait values; slope of best fit line gives estimate of heritability

Question 28

What does a slope of 0 for a plot of midoffspring trait values vs. midparent trait values indicate? A slope of 1?

Answer 28

o Slope of 0 – no resemblance o Slope of 1 – perfect resemblance

Question 29

What are the 4 confounding issues that can complicate heritability estimates based off of graphs/

Answer 29

Misidentified paternity Conspecific nest parasitism Shared environments Maternal effects

Question 30

What is misidentified paternity and how can it be avoided?

Answer 30

o Social father is not biological father o Can be avoided using genetic paternity tests

Question 31

What is conspecific nest parasitism? How can this be avoided?

Answer 31

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

Question 32

How can shared environments complicate heritability estimateS?

Answer 32

o Relatives share their environment as well as their genes o Correlation due to shared environment inflates heritability measurements

Question 33

What is a possible solution to the complications in heritability estimates due to shared environments?

Answer 33

 Cross-fostering/common garden/reciprocal-transplant experiments

Question 34

What are maternal effects? How can these be avoided?

Answer 34

o Differences in the nutrient stores or hormonal contents of eggs o Avoid by estimating heritabilities from fathers only

Question 35

Outline the three steps in measuring diversity at a particular gene.

Answer 35

1. Determine the genotypes of a large sample a. Typically look at DNA 2. 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 3. Summarize data (two possible statistics)

Question 36

What are the two possible statistics in measuring diversity of alleles at a particular gene?

Answer 36

Mean heterozyogisty Percentage of polymorphic loci

Question 37

What is mean heterozygosity?

Answer 37

i. Average frequency of heterozygotes across loci/fraction of genes that are heterozygous in the genotype of the average individual

Question 38

What is percentage of polymorphic loci?

Answer 38

i. Fraction of genes in a population that have at least 2 alleles

Question 39

How do you calculate the probability that two independent events will occur together?

Answer 39

Product of individual probabilities

Question 40

How do you calculate the probability that one or the other of two mutually exclusive events will occur?

Answer 40

Sum of individual probabilities

Question 41

What is the HWE Principle with more than two alleles?

Answer 41

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.

Question 42

What are the five steps of the statsitiscal analysis of allele and genotype frequencies using the chi square test?

Answer 42

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

Question 43

How do you determine whether the test statistic is significant?

Answer 43

a. Calculate degrees of freedom i. # of classes - # of independent values calculated from the data b. Use table to find critical value