Lecture 10

Question 1

Genome-wide association studies

Answer 1

• seek correlations between SNP patterns and phenotype in large groups of individuals
• seek SNPs that are shared with much greater frequency among individuals with the same trait than among others

Question 2

SNPs (single nucleotide polymorphisms)

Answer 2

• sites in a genome where the DNA base varies in at least 1% of the population
• SNPs span the genome, rather than define a single gene (can be anywhere among our roughly 3.3 billion base pairs)

Question 3

Study designs

Answer 3

• cohort study
• case-control study
• “affected sibling pair” strategy
• homozygosity mapping

Question 4

The “affected sibling pair” strategy

Answer 4

scans genomes of siblings for SNPs shared by those with the condition, but not by those who don’t have it

Question 5

homozygosity mapping

Answer 5

performed on families that are consanguineous - the children in this case are more likely to inherit two copies of the mutation

Question 6

limitations of genome-wide association studies

Answer 6

1. they include many data points and so are prone to error (false positives)
2. they reveal associations between two types of information, not causes
3. bias can be introduced in the way the patient population is selected
4. their accuracy is affected by complicating factors, such as phenocopy and epistasis
5. they may miss extremely rare SNPs

Question 7

gene pool

Answer 7

the collection of all alleles in the members of the population

Question 8

population genetics

Answer 8

the study of the genetics of a population and how the alleles vary with time

Question 9

gene flow

Answer 9

movement of alleles between populations when people migrate and mate

Question 10

microevolution

Answer 10

the small genetic changes due to changing allelic frequencies in populations

five factors:

1) nonrandom mating
2) migration
3) genetic drift
4) mutation
5) natural selection

Question 11

macroevolution

Answer 11

• refers to the formation of new species
• occurs when enough microevolutionary changes have occurred to prevent individuals from two different populations from interbreeding to successfully produce fertile offspring

Question 12

Hardy-weinberg equation

Answer 12

explains how allele frequencies predict genotypic and phenotypic frequencies in a population of diploid, sexually–reproducing species

Question 13

what did hardy-weibberg disprove

Answer 13

disproved the assumption that dominant traits would become more common, while recessive traits would become rarer

Question 14

Hardy-weinberg equilibrium

Answer 14

allele and genotypic frequencies do not change from one generation to the next

Question 15

What’s uncommon for hardy-weinberg equilibrium?

Answer 15

it is uncommon for mutation in protein-encoding genes that affect the phenotype

but it does apply to mutations in portions of the genome that do not have a large affect on phenotype

these include many repeated DNA segments - “neutral variants that are not subject to natural selection

Question 16

What is DNA repeats and what are the two types of repeats

Answer 16

Short repeated segments that can be considered as alleles and used to classify individuals

1) Variable number of tandem repeats (VNTRs) - minisatellites
2) Short tandem repeats (STRs) - microsatellites

Question 17

DNA profiling

Answer 17

-a technique that detects differences in repeat copy number

Question 18

what does DNA profiling calculate?

Answer 18

the probability that certain combinations can occur in two sources of DNA by chance
-DNA evidence is more often valuable in excluding a suspect

Question 19

Who is DNA profiling developed by?

Answer 19

by British geneticist Sir Alec Jeffreys in the 1980s

Question 20

What is another name for DNA profiling?

Answer 20

DNA fingerprinting because it identifies individuals

Question 21

Polymerase chain reaction

Answer 21

2 primers complementary to 3’ end of sense and antisense strands of DNA

heat tolerant Taq DNA polymerase

Question 22

DNA sources

Answer 22

• DNA obtained from any cell with a nucleus
• STR (amplified via PCR) are useful when DNA is scarce
• if DNA is extremely damaged, mitochondrial DNA (mtDNA) is sometimes used
• for forensics, the FBI developed the Combined DNA Index System (CODIS) - uses 13 STRs

Question 23

CODIS

Answer 23

The probability that any two individuals have same 13 markers is 1 in 250 trillion

Question 24

How is DNA profiling expanded?

Answer 24

by tracking repeats in different chromosomes - the number of copies of a repeat are assigned probabilities based on their observed frequencies in a population